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Climate change has been intensifying soil drying and rewetting cycles, which can alter the soil microbiome structure and activity. Here we hypothesized that a soil drying-rewetting cycle enhances biodegradation and, hence, decreases the effectiveness of nitrification inhibitors (NIs). The effectiveness of DMPP (3,4-Dimethylpyrazole phosphate) and MP + TZ (3-Methylpyrazol and Triazol) was evaluated in 60-day incubation studies under a drying and rewetting cycle relative to constant low and high soil moisture conditions (40% and 80% water-holding capacity, WHC, respectively) in two different textured soils. The measurements included (i) daily and cumulative N2O-N emissions, (ii) soil NH4+-N and NO3−-N concentrations, and (iii) the composition of bacterial soil communities. Application of DMPP and MP + TZ reduced the overall N2O-N emissions under drying-rewetting (-45%), as well as under 40% WHC (-39%) and 80% WHC (-25%). DMPP retarded nitrification and decreased N2O-N release from the sandy and silt loam soils, while MP + TZ mitigated N2O-N production only from the silt loam soil. Unexpectedly, between days 30 and 60, N2O-N emissions from NI-treated soils increased by up to fivefold relative to the No-NI treatment in the silt loam soil at 80% WHC. Likewise, the relative abundance of the studied nitrifying bacteria indicated that the NIs had only short-term effectiveness in the silt loam soil. These results suggested that DMPP and MP + TZ might trigger high N2O-N release from fine-textured soil with constant high moisture after this short-term inhibitory effect. In conclusion, DMPP and MP + TZ effectively reduce N2O-N emissions under soil drying and rewetting. [ABSTRACT FROM AUTHOR]

Climate change alters environmental conditions in ways that directly and indirectly affect plants. Flowering plants, for example, modify reproductive allocation in response to heat and drought stress, and such changes can in turn affect pollinator visitation and, ultimately, plant reproduction. Although the individual effects of warming and drought on plant reproductive allocation are well known, these factors may interact to influence reproduction. Here, we conducted a fully crossed temperature by irrigation manipulation in squash (Cucurbita pepo) to test how temperature and soil moisture variation affect pollinator‐mediated reproduction. To tease apart the direct and indirect effects of temperature and soil moisture, we compared hand‐pollinated plants to bee‐pollinated plants and restricted bee foraging (i.e., pollen transfer) to one experimental group per day. Temperature and soil‐moisture limitation acted independently of one another: warming decreased flower size and increased pollen production, whereas the effects of soil‐moisture limitation were uniformly inhibitory. While treatments did not change squash bee (Xenoglossa spp.) behavior, floral visitation by the honey bee (Apis mellifera) increased with temperature in male flowers and decreased with soil moisture in female flowers. Pollen deposition by bees was independent of plant soil moisture, yet reducing soil moisture increased pollen limitation. This result stemmed at least in part from the effects of soil‐moisture limitation on pollen viability; seed set declined with increasing deposition of fluorescent pigment (a proxy for pollen) from plants experiencing decreased soil moisture. These findings suggest that the transfer of lower‐quality pollen from plants experiencing soil‐moisture limitation led to drought‐induced pollen limitation. Similar effects may occur in a wide variety of flowering plant species as climate warming and drought increasingly impact animal‐pollinated systems. [ABSTRACT FROM AUTHOR]

Summary: Understanding the capacity of temperate trees to acclimate to limited soil water has become essential in the face of increasing drought risk due to climate change. We documented seasonal – or phenological – patterns in acclimation to water deficit stress in stems and leaves of tree species spanning the angiosperm phylogeny.Over 3 yr of field observations carried out in two US arboreta, we measured stem vulnerability to embolism (36 individuals of 7 Species) and turgor loss point (119 individuals of 27 species) over the growing season. We also conducted a growth chamber experiment on 20 individuals of one species to assess the mechanistic relationship between soil water restriction and acclimation.In three‐quarters of species measured, plants became less vulnerable to embolism and/or loss of turgor over the growing season. We were able to stimulate this acclimatory effect by withholding water in the growth chamber experiment.Temperate angiosperms are capable of acclimation to soil water deficit stress, showing maximum vulnerability to soil water deficits following budbreak and becoming more resilient to damage over the course of the growing season or in response to simulated drought. The species‐specific tempo and extent of this acclimatory potential constitutes preadaptive climate change resilience. [ABSTRACT FROM AUTHOR]

Anthropogenic climate change has already affected drought severity and risk across many regions, and climate models project additional increases in drought risk with future warming. Historically, droughts are typically caused by periods of below‐normal precipitation and terminated by average or above‐normal precipitation. In many regions, however, soil moisture is projected to decrease primarily through warming‐driven increases in evaporative demand, potentially affecting the ability of negative precipitation anomalies to cause drought and positive precipitation anomalies to terminate drought. Here, we use climate model simulations from Phase Six of the Coupled Model Intercomparison Project (CMIP6) to investigate how different levels of warming (1, 2, and 3°C) affect the influence of precipitation on soil moisture drought in the Mediterranean and Western North America regions. We demonstrate that the same monthly precipitation deficits (25th percentile relative to a preindustrial baseline) at a global warming level of 2°C increase the probability of both surface and rootzone soil moisture drought by 29% in the Mediterranean and 32% and 6% in Western North America compared to the preindustrial baseline. Furthermore, the probability of a dry (25th percentile relative to a preindustrial baseline) surface soil moisture month given a high (75th percentile relative to a preindustrial baseline) precipitation month is 6 (Mediterranean) and 3 (Western North America) times more likely in a 2°C world compared to the preindustrial baseline. For these regions, warming will likely increase the risk of soil moisture drought during low precipitation periods while simultaneously reducing the efficacy of high precipitation periods to terminate droughts. Plain Language Summary: Regional warming associated with climate change is already making droughts worse in many places. This trend is expected to continue as global temperatures increase in response to continued emissions of greenhouse gases. With increasing temperatures, soils are projected to lose water to the atmosphere as it draws more and more moisture from the land surface, increasing drought risk. At the same time, climate change is also projected to shift precipitation patterns. This means it is important to understand how changes in rainfall will cause and end droughts in the future. Using state‐of‐the‐art climate models, we investigate how future warming will impact the influence of precipitation on soil moisture in the Mediterranean and Western North America. Our results suggest that current levels of monthly precipitation will be insufficient to alleviate drought conditions in a warmer world. Key Points: Warming causes declines in soil moisture in the Mediterranean and Western North AmericaThe probability of a moderate soil moisture drought increases during both low and high precipitation anomalies, even at 1°C of warmingThe ability of large positive precipitation anomalies to terminate soil moisture droughts will be substantially reduced in a warmer world [ABSTRACT FROM AUTHOR]

Global food security faces a substantial risk stemming from water scarcity, particularly in regions heavily dependent on rainfall for agricultural purposes. In the Andean region, which is grappling with water scarcity, innovative and sustainable approaches are imperative for securing food sources. Plastic mulching has emerged as a potential solution to address water scarcity challenges by conserving soil moisture and optimizing growing conditions. A two-year field experiment was conducted that evaluated the efficacy of plastic mulching in preserving soil water content and reducing drought stress for maize. Two maize cultivars were grown with plastic mulching and conventional practices using a randomized completed block design with three replicates. The results demonstrated that employing plastic mulch led to a rise in the soil water content, particularly within the initial 30 cm of depth, resulting in variances of up to 4.71% humidity between the 20 and 30 cm depths. For the 2019 and 2020 evaluation years, plastic mulching elevated the volumetric water content in the first 30 cm of the soil by 8.39% and 14.18%, respectively. Additionally, it elevated the soil temperature by 1.26 °C and reduced the maize flowering time. Plastic mulching substantially enhanced the fresh corn yield, reaching a 162% increase compared to conventional plots. These findings underscore the potential benefits of plastic mulching in conserving the soil water content, alleviating drought and cold stress for crops in the Andean region. [ABSTRACT FROM AUTHOR]

This study evaluated the impacts of climate change on hydro-meteorological droughts in the Chao Phraya River Basin (CPRB), Thailand under two Representative Concentration Pathway (RCP) scenarios (RCP4.5 and RCP8.5). We used three Reginal Climate Models (RCMs) of the Southeast Asia Regional Climate Downscaling/Coordinated Regional Climate Downscaling Experiment—Southeast Asia (SEACLID/CORDEX-SEA), which are bias corrected. The Soil and Water Assessment Tool (SWAT) was used to simulate streamflow for future periods. The Standardized Precipitation Index (SPI) and Standardized Streamflow Index (SSI) were estimated and used for drought characterization at three time scales (3, 6, and 12 months). The lag time between meteorological and hydrological droughts is approximately 1–3 months. The results suggest that the CPRB is likely to experience less frequent hydro-meteorological drought events in the future. The meteorological drought is projected to be longer, more severe, and intense. The severity of hydrological drought tends to decrease, but the intensity could increase. Climate change has been discovered to alter drought behaviors in the CPRB, posing a threat to drought monitoring and warning because droughts will be less predictable in future climate scenarios. The characterization of historical and future droughts over the CPRB is therefore valuable in developing an improved understanding of the risks of drought. [ABSTRACT FROM AUTHOR]

Global climate change is expected to increase the frequency and intensity of extreme droughts. Researching tree growth responses to drought helps assess the potential of forest adaptation and ecological stability under changing climate conditions. Here, we investigated tree growth resilience components (resistance, recovery, and resilience) to extreme drought events of two mainly distributed species, Pinus tabulaeformis and Picea wilsonii, on the Gannan Plateau, the Eastern Tibetan Plateau. Tree-ring width data from 510 trees at 20 plots along the elevation gradients were employed to analyze the tree resilience components at the individual tree level. The results showed that P. tabulaeformis had a lower growth resistance and a higher recovery capacity to drought than P. wilsonii, which might be related to the different strategies for combating drought of the two species. In addition, the tree growth response of P. tabulaeformis to drought changed significantly along the elevation gradient due to its higher drought sensitivity than that of P. wilsonii. Overall, the long-term correlation between tree growth and drought index, tree size, and soil water content had implications for tree growth resistance, recovery, and resilience. Given the observed differences in tree growth resistance to drought among different species and environmental conditions, a well-thought-out and tailored strategy would better support forest management on the Gannan Plateau. [ABSTRACT FROM AUTHOR]

A combination of annual peak water demand due to seasonal population spikes along with small and shallow aquifers has prompted an assessment of the region's watersheds as operating at a net water deficit. This study uses the Soil and Water Assessment Tool (SWAT) to simulate historical drought conditions in the Chipuxet watershed in Rhode Island, USA. The calibrated and validated model uses the Soil Moisture Deficit Index (SMDI) and Evapotranspiration Deficit Index (ETDI) as well as an Indicators of Hydrological Alteration (IHA) calculation to determine the frequency and severity of historical droughts and to simulate climate change conditions developed through a downscaled climate model selection. The output data for the historical and climate change scenarios were analyzed for drought frequency and severity. Results indicate that water stress will increase in both low-emission (RCP4.5) and high-emission (RCP8.5) scenarios. Additionally, the SMDI and ETDI show that RCP8.5 climate scenarios will have more severe deficits. Finally, IHA data indicate that zero-flow days and low-flow durations increase under all climate scenarios. [ABSTRACT FROM AUTHOR]

We review results from field experiments that simulate drought, an ecologically impactful global change threat that is predicted to increase in magnitude, extent, duration and frequency. Our goal is to address, from primarily an ecosystem perspective, the questions 'What have we learned from drought experiments?' and 'Where do we go from here?'.Drought experiments are among the most numerous climate change manipulations and have been deployed across a wide range of biomes, although most are conducted in short‐statured, water‐limited ecosystems. Collectively, these experiments have enabled ecologists to quantify the negative responses to drought that occur for most aspects of ecosystem structure and function. Multiple meta‐analyses of responses have also enabled comparisons of relative effect sizes of drought across hundreds of sites, particularly for carbon cycle metrics. Overall, drought experiments have provided strong evidence that ecosystem sensitivity to drought increases with aridity, but that plant traits associated with aridity are not necessarily predictive of drought resistance. There is also intriguing evidence that as drought magnitude or duration increases to extreme levels, plant strategies may shift from drought tolerance to drought escape/avoidance.We highlight three areas where more drought experiments are needed to advance our understanding. First, because drought is intensifying in multiple ways, experiments are needed that address alterations in drought magnitude versus duration, timing and/or frequency (individually and interactively). Second, drivers of drought may be shifting—from precipitation deficits to rising atmospheric demand for water—and disentangling how ecosystems respond to changes in hydrological 'supply versus demand' is critical for understanding drought impacts in the future. Finally, more attention should be focussed on post‐drought recovery periods since legacies of drought can affect ecosystem functioning much longer than the drought itself.We conclude with a call for a fundamental shift in the focus of drought experiments from those designed primarily as 'response experiments', quantifying the magnitude of change in ecosystem structure and function, to more 'mechanistic experiments'—those that explicitly manipulate ecological processes or attributes thought to underpin drought responses. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Abstract Anthropogenic climate change has already affected drought severity and risk across many regions, and climate models project additional increases in drought risk with future warming. Historically, droughts are typically caused by periods of below‐normal precipitation and terminated by average or above‐normal precipitation. In many regions, however, soil moisture is projected to decrease primarily through warming‐driven increases in evaporative demand, potentially affecting the ability of negative precipitation anomalies to cause drought and positive precipitation anomalies to terminate drought. Here, we use climate model simulations from Phase Six of the Coupled Model Intercomparison Project (CMIP6) to investigate how different levels of warming (1, 2, and 3°C) affect the influence of precipitation on soil moisture drought in the Mediterranean and Western North America regions. We demonstrate that the same monthly precipitation deficits (25th percentile relative to a preindustrial baseline) at a global warming level of 2°C increase the probability of both surface and rootzone soil moisture drought by 29% in the Mediterranean and 32% and 6% in Western North America compared to the preindustrial baseline. Furthermore, the probability of a dry (25th percentile relative to a preindustrial baseline) surface soil moisture month given a high (75th percentile relative to a preindustrial baseline) precipitation month is 6 (Mediterranean) and 3 (Western North America) times more likely in a 2°C world compared to the preindustrial baseline. For these regions, warming will likely increase the risk of soil moisture drought during low precipitation periods while simultaneously reducing the efficacy of high precipitation periods to terminate droughts.

Elevated temperature and frequent drought events under global climate change may seriously affect soil respiration. However, the underlying mechanism of the effects of warming and drought on soil respiration is not fully understood in the context of the Loess Plateau. This study examined the response of soil respiration (Rs) to multiple factors, including warming (W), drought (P), and their interaction (WP), in the semi-arid grassland of the Loess Plateau in Northwest China. The research period was from May to November 2022, with an open-top heating box used for warming and a rain shelter used for drought. The results showed the following: (1) Rs ranged from 1.67 μmol m−2 s−1 to 4.77 μmol m−2 s−1, with an average of 3.36 ± 0.07 μmol m−2 s−1. The cumulative soil carbon flux ranged from 500.97 g C·m−2 to 566.97 g C·m−2, and the average cumulative soil respiration was 535.28 ± 35.44 g C·m−2. (2) Warming increased Rs by 5.04 ± 3.11%, but drought inhibited Rs by 3.40 ± 3.14%, and the interaction between warming and drought significantly reduced soil respiration by 11.27 ± 3.89%. (3) The content of particulate organic carbon (POC), dissolved organic carbon (DOC), soil organic carbon (SOC), and readily oxidized carbon (ROC) decreased with the increased soil depth. ROC after W and WP treatments was significantly higher than that of the control, and POC after P treatment was significantly higher than CK (p < 0.05). (4) The seasonal variation of soil respiration was positively correlated with soil temperature, soil water content, plant height, and leaf area index (p < 0.05), but the response rules differed during different regeneration periods. Soil water content; soil water content and leaf area index; and soil water content, soil temperature, and leaf area index were the factors that regulated the variation in soil respiration in the first, second, and third regeneration periods, respectively. These results clearly showed the limiting effect of drought stress on the coupling between temperature and soil respiration, especially in semi-arid regions. Collectively, the variations in soil respiration under warming, drought, and their interactions were further regulated by different biotic and abiotic factors. Considering future warming, when coupled with increased drought, our findings indicate the importance of considering the interactive effects of climate change on soil respiration and its components in arid and semi-arid regions over the next decade. [ABSTRACT FROM AUTHOR]

The increasing frequency of fires is a major threat to biodiversity around the world, further facilitated by global warming. Fires usually affect insect populations directly, but insect eggs may partly be protected from wildfires when oviposited into the ground. Madeira belongs to the Macaronesian islands which experience wildfires annually. The Madeiran Green Bush-Cricket (Psalmatophanes barretoi) is endemic to the island and listed on the IUCN Red List as Vulnerable with wildfires being named as the major threat to the species. However, it remains unclear whether the eggs of P. barretoi may be partly protected from fires due to the oviposition substrate (soil). It also remains unknown whether increased temperature alone or increased drought are more important drivers of mortality when fires are approaching or surpassing an oviposition site. We hypothesized that drought might have a significant effect on mortality when heat levels remain slightly below or above mortal temperatures. Therefore, we tested the effects of temperature and drought on egg survival in two laboratory experiments by incubating eggs at different temperatures (49 °C, 55 °C) for six hours with and without water replacement. Our results show that the combination of drought and heat affected egg mortality significantly stronger than heat alone. As a result, we conclude that egg mortality is strongly mediated by soil desiccation and that eggs might be buffered from fire effects in moist habitats or after increased rainfall. Implications for insect conservation: Our results suggest that soil moisture is a key variable to mitigate egg mortality from wildfires. This can be reached by protecting habitats with high soil moisture (e.g. laurel forests and many native bushes) or by prescribed burning during the winter months when soil moisture is higher than in summer. [ABSTRACT FROM AUTHOR]

Summary: Accounting for water limitation is key to determining vegetation sensitivity to drought. Quantifying water limitation effects on evapotranspiration (ET) is challenged by the heterogeneity of vegetation types, climate zones and vertically along the rooting zone.Here, we train deep neural networks using flux measurements to study ET responses to progressing drought conditions. We determine a water stress factor (fET) that isolates ET reductions from effects of atmospheric aridity and other covarying drivers. We regress fET against the cumulative water deficit, which reveals the control of whole‐column moisture availability.We find a variety of ET responses to water stress. Responses range from rapid declines of fET to 10% of its water‐unlimited rate at several savannah and grassland sites, to mild fET reductions in most forests, despite substantial water deficits. Most sensitive responses are found at the most arid and warm sites.A combination of regulation of stomatal and hydraulic conductance and access to belowground water reservoirs, whether in groundwater or deep soil moisture, could explain the different behaviors observed across sites. This variety of responses is not captured by a standard land surface model, likely reflecting simplifications in its representation of belowground water storage. [ABSTRACT FROM AUTHOR]

The linkage of stomatal behaviour with photosynthesis is critical to understanding water and carbon cycles under global change. The relationship of stomatal conductance (gs) and CO2 assimilation (Anet) across a range of environmental contexts, as represented in the model parameter (g1), has served as a proxy of the marginal water cost of carbon acquisition. We use g1 to assess species differences in stomatal behaviour to a decade of open‐air experimental climate change manipulations, asking whether generalisable patterns exist across species and climate contexts. Anet‐gs measurements (17 727) for 21 boreal and temperate tree species under ambient and +3.3°C warming, and ambient and ~40% summer rainfall reduction, provided >2700 estimates of g1. Warming and/or reduced rainfall treatments both lowered g1 because those treatments resulted in lower soil moisture and because stomatal behaviour changed more in warming when soil moisture was low. Species tended to respond similarly, although, in species from warmer and drier habitats, g1 tended to be slightly higher and to be the least sensitive to the decrease in soil water. Overall, both warming and rainfall reduction consistently made stomatal behaviour more conservative in terms of water loss per unit carbon gain across 21 species and a decade of experimental observation. [ABSTRACT FROM AUTHOR]

Monthly temperature and precipitation data for 923 United States Geological Survey 8‐digit hydrologic units are used as inputs to a monthly water balance model to compute monthly actual evapotranspiration, soil moisture storage, and runoff across the western United States (U.S.) for the period 1900 through 2020. Time series of these water balance variables are examined to characterize and explain the dry conditions across the western U.S. since the year 2000. Results indicate that although precipitation deficits account for most of the changes in actual evapotranspiration and runoff, increases in temperature primarily explain decreases in soil moisture storage. Specifically, temperature has been particularly impactful on the magnitude of negative departures of soil moisture storage during the spring (April through June) and summer (July through September) seasons. These effects on soil moisture may be particularly detrimental to agriculture in regions already stressed by drought such as the western U.S. [ABSTRACT FROM AUTHOR]

Net primary productivity (NPP) is a key ecosystem function of plant communities. Climate change is expected to affect NPP both directly and indirectly through associated edaphic and plant community factors. Changes in soil nutrients, plant species richness and/or functional group dominance may amplify or counteract direct climatic effects on NPP, and responses may differ above-versus belowground, making it challenging to predict the net effects on NPP. In this study, we manipulated temperature and precipitation at four sites spanning a latitudinal Mediterranean-climate gradient in the Pacific Northwest, USA, and measured aboveground, belowground, and total NPP responses in experimentally assembled prairie plant communities. Using structural equation models, we disentangled the direct effects of climate from its indirect effects through soil nutrient availability and plant community responses. We found that warming, primarily by reducing soil moisture (that is, drying), had a net negative effect on all aspects of NPP, but these negative effects were partially ameliorated by increasing nitrogen and phosphorus availability, as well as changes to the plant community. Specifically, warming, drying, and greater nutrient availability caused species richness to decline, leading to greater dominance by a restricted set of functional groups, which positively affected aboveground NPP. Furthermore, a shift from perennial grass to annual grass dominance increased the ratio of aboveground to belowground NPP. Our results demonstrate that the indirect effects of climate change can help partially buffer the negative direct effects on NPP in Mediterranean-climate prairies. However, increasing soil moisture limitation may still overwhelm the positive effects of such intermediary pathways. [ABSTRACT FROM AUTHOR]

This study investigates the relationship between soil moisture and the growth of Pinus halepensis, P. nigra, P. sylvestris and P. uncinata, which are some of the main pine species of the Iberian Peninsula, and the response of these species to soil drought. The role played by climatic and geographic factors in the resilience of these species to drought events is also evaluated. A total of 110 locations of the four species studied were selected, with data ranging from 1950 to 2007. The results show that the species that are less dependent on soil moisture best withstood droughts, while those more dependent on it showed better adaptability. Additionally, climatic and geographic factors had a stronger influence on the species' resilience to soil drought at higher altitudes. The results of this study can help us to better understand forest ecosystem dynamics and their reaction to droughts in Mediterranean areas, where this phenomenon will be much more severe in the future due to climate change. [ABSTRACT FROM AUTHOR]

Deep soil drought represents a low level of deep soil water status that is unsuitable for vegetation growth and transpiration. It can be exacerbated through the excessive water uptake by vegetation during climate droughts, while signs of deep soil drought remain unclear worldwide due to a lack of unified methods and comparative data. In this study, we performed a literature search, focusing on deep soil water profiles (>2 m) and quantification of the degree of deep soil drought as indicated by dried soil layers (DSLs). The results revealed the following: (1) DSLs were distributed worldwide, with mean values of 2.2 ± 0.5 m, 3.3 ± 3.9 m, 14.6% ± 8.3%, and 0.66 ± 0.14 for the formation depth, thickness, soil water content, and quantitative index, respectively; (2) at the global scale, DSLs were more common and more severe under forestland, including shrubland, than under grassland and farmland; (3) DSLs were shaped directly by rooting depth and soil particle composition and indirectly by land use, soil thickness, terrain, and climate. The preliminary investigation of DSL distribution confirms the existence of DSLs globally, something that has not been addressed in previous studies. Our study provides an early warning of DSL formation in association with rooting depth and soil particle composition under an increased drought condition, which in turn harms vegetation production and sustainability. [ABSTRACT FROM AUTHOR]

Standardized precipitation index (SPI) is one of the frequently used meteorological drought indices. However, the time-varying characteristics observed in the historical precipitation data questions the reliability of SPI and motivated the development of nonstationary SPI. To overcome some of the limitations in the existing nonstationary drought indices, a new framework for drought index is proposed, incorporating the temporal dynamics in the precipitation. The proposed drought index is developed by coupling the joint deficit index with the extended time sliding window–based nonstationary modeling (TSW-NSM). The proposed nonstationary joint deficit index (NJDI) detects the signature of nonstationarity in the distribution parameter and models both long-term (i.e., trend) and short-term (i.e., step-change) temporal dynamics of distribution parameters. The efficacy of NJDI is demonstrated by employing it to identify the meteorological drought-prone areas over India. The changes observed in the distribution parameter of rainfall series reveal an increasing number of dry days in recent decades all over India, except the northeast. Comparison of NJDI and stationary joint deficit index (JDI) reveals that JDI overestimates drought when frequent severe dry events are clustered and underestimates when these events are scattered, which indicates that the traditional index is biased toward the lowest magnitude of precipitation while classifying the drought. Moreover, NJDI could closely capture historical droughts and their spatial variations, thereby reflecting the temporal dynamics of rainfall series and the changes in the pattern of dry events over India. NJDI proves to be a potentially reliable index for drought monitoring in a nonstationary climate. Significance Statement: Drought is one of the most severe natural disasters and is expected to intensify under a warming climate. There has been progress on developing newer methodologies to characterize drought severity under the changing climate. However, some limitations remain in capturing the temporal changes of the precipitation, especially the nonstationarity in variance (rapid increases in extreme precipitation versus the average precipitation). We propose an extension to the time sliding window approach to capture the nonstationarity in variance and mean while incorporating short-term (step-change) and long-term (trend) temporal dynamics. We apply the methodology to a subcontinent-sized heterogeneous country of India with gridded rainfall dataset (0.25° × 0.25°, 1901–2013) from the India Meteorological Department. We find that the majority of grids exhibit negative and positive trends in shape and scale parameters, respectively, which ultimately leads to an increase in the number of drier events, whereas a contradictory pattern is exhibited in the northwest Indian region (decrease in the number of dry days). The proposed index gives a potential framework for drought monitoring under the changing climate and can be extended to develop a multivariate nonstationary joint deficit index by incorporating other hydrological variables (e.g., soil moisture, diurnal temperature range, streamflow). [ABSTRACT FROM AUTHOR]

The peak growth of plant in summer is an important indicator of the capacity of terrestrial ecosystem productivity, and ongoing studies have shown its responses to climate warming as represented in the mean temperature. However, the impacts from the asymmetrical warming, that is, different rates in the changes of daytime (Tmax) and nighttime (Tmin) warming were mostly ignored. Using 60 flux sites (674 site‐year in total) measurements and satellite observations from two independent satellite platforms (Global Inventory Monitoring and Modeling Studies [1982–2015]; MODIS [2000–2020]) over the Northern Hemisphere (≥30°N), here we show that the peak growth, as represented by both flux‐based maximum primary productivity and the maximum greenness indices (maximum normalized difference vegetation index and enhanced vegetation index), responded oppositely to daytime and nighttime warming. Tmax−Tmin+ (peak growth showed negative responses to Tmax, but positive responses to Tmin) dominated in most ecosystems and climate types, especially in water‐limited ecosystems, while Tmax+Tmin− (peak growth showed positive responses to Tmax, but negative responses to Tmin) was primarily observed in high latitude regions. These contrasting responses could be explained by the strong association between asymmetric warming and water conditions, including soil moisture, evapotranspiration/potential evapotranspiration, and the vapor pressure deficit. Our results are therefore important to the understanding of the responses of peak growth to climate change, and consequently a better representation of asymmetrical warming in future ecosystem models by differentiating the contributions between daytime and nighttime warming. [ABSTRACT FROM AUTHOR]

Droughts and floods are extreme events that have tremendous socioeconomic impact. Many studies have investigated their possible variations under the effects of climate changes, while their intraseasonal‐to‐seasonal characteristics have received less attention. Based on observation‐constrained monthly soil moisture (SM) datasets since 1980, we analysed the spatiotemporal characteristics of global SM at the intraseasonal‐to‐seasonal time scales and the associated influencing factors. The results were then used to evaluate the performance of simulations by Coupled Model Intercomparison Project Phase 6 (CMIP6) models. It is found that the frequencies of extreme wet events are slightly higher than those of extreme dry events, but their spatial distributions are similar and are both affected by precipitation variability. Extreme events tend to have longer durations than nonextreme events, and their global mean durations are 4–5 months. Globally, dry events persist longer than wet events. Maximum SM anomalies are strongly affected by earlier precipitation and this effect is stronger in a transitional climate. The onset and peak times of SM anomalies in a year occur most frequently near the peak time of precipitation rather than that of SM. Approximately half of CMIP6 models overestimate the durations of both dry and wet events and approximately one third of models only underestimate wet events durations. Different versions of the same model produce similar event durations. The findings of this study enhance understanding of the intraseasonal‐to‐seasonal variabilities of global droughts and floods and could provide guidance for future study of land–atmosphere interactions and prediction of extreme events. [ABSTRACT FROM AUTHOR]

The frequency and severity of droughts in the Alps are expected to increase due to rising air temperatures and changes in precipitation regimes. Although biomass production in humid mountain areas tends to be energy limited rather than water limited, an increase in droughts may have negative impacts on the water availability and thus agricultural yields. This study aimed to analyse the impacts of dry spells on soil moisture and yield anomalies at a montane permanent grassland site in Austria. Dry spells in the time period from 2018 to 2020 were identified using the Standardized Precipitation Index, Palmer Drought Severity Index and the Soil Moisture Anomaly Index. Data from a lysimeter climate experiment were used to evaluate drought impacts on soil water storage and grassland yield under ambient and manipulated conditions. The results indicated the occurrence of three extreme droughts between 2018 and 2020. Although the studied grassland is generally considered a nonwater‐limited ecosystem, the most extreme drought in summer 2019 caused severe and extreme yield anomalies under ambient and heated conditions. Only mild yield anomalies were observed on plots with elevated atmospheric carbon dioxide concentration. This drought‐mitigating effect was attributed to the water savings enabled by partial stomatal closure under elevated CO2. The shorter dry spells in spring and late summer 2018 led to more diverse effects; mildly to moderately negative yield anomalies were found on the heated plots, whereas the anomalies tended to be less negative or even positive on plots under ambient temperature. In contrast, some time periods without water stress showed positive effects of heating on yield. These findings suggest that drought impacts on a humid montane grassland depend on both water availability and air temperature. Higher air temperature can have positive effects on yield if the ecosystem is energy limited. However, global warming suggests a tendency from energy to water limitation, in which the increased evaporative demand of the atmosphere aggravates soil moisture droughts and thus has potentially negative effects on yield. [ABSTRACT FROM AUTHOR]

This work presents results from a field experiment which was focused on the impact of the drought period on microbial activities in rhizosphere and non-rhizosphere soil. To demonstrate the effect of drought, the pot experiment lasted from 2012 to 2015. Fifteen lysimeters (plastic containers) were prepared in our area of interest. These lysimeters were filled with the subsoil and topsoil from this area and divided into two groups. The first group consisted of two variants: V1 (control) and V2 (84 kg N/ha), which were not stressed by drought. The second group consisted of three variants, V3 (control), V4 (84 kg N/ha), and V5 (84 kg N/ha + 1.25 L lignohumate/ha), which were stressed by drought every year of the experiment for 30 days. Changes in the soil moisture content caused by drought significantly affect the growth of Deschampsia caespitosa L., the microbial activity, and the soil's capacity to retain nutrients. The measured basal respiration and dehydrogenase activity values confirm the significant effect of drought on microbial activity. These values were demonstrably higher in the period before drought simulation by more than 60%. On the other hand, significant differences between microbial activities in the rhizosphere and non-rhizosphere soil were not found. We did not find a clear effect of drought on the formation of soil water repellency. [ABSTRACT FROM AUTHOR]

Drought is a recurring natural hazard that has substantial human and environmental impacts. Given continued global warming and associated climate change, there is concern that droughts could become more severe and longer lasting. To better monitor and understand drought development and persistence, it is helpful to understand the development and climatic drivers of past droughts. In this study we use monthly runoff percentiles to identify five major drought events in the conterminous United States (CONUS) from 1901 through 2020. For each drought event we examined spatial patterns of departures of mean monthly precipitation, temperature, soil moisture storage, and runoff for 2,107 hydrologic units (HUs) across the CONUS. Results indicated that precipitation deficits have been the primary driver of past major‐drought events and temperature a secondary driver, even of the most recent drought event (September 1999 through September 2015) when positive temperature anomalies occurred over most of the CONUS. Additionally, negative soil moisture storage departures were more negative than runoff departures during the five drought events we examined, which emphasizes the importance of measuring both runoff and soil moisture to monitor drought conditions. We also examined the use of statistical persistence to develop short‐term (i.e., 1 month) forecasts of runoff drought conditions in the CONUS by developing autoregressive integrated moving average (ARIMA) models for each HU. Results indicated that persistence can be used to predict short‐term changes in the spatial pattern of drought and the areal extent of drought, but that predictions of runoff magnitude for any particular site are often poor. [ABSTRACT FROM AUTHOR]

Climate change is increasing the severity and duration of drought events experienced by forest ecosystems. Because water is essential for tree physiological processes, the ability of trees to survive prolonged droughts will largely depend on whether they have access to reliable water sources. While many woody plant species exhibit the ability to shift water sources between different depths of soil and rock water in response to changes in climate and water availability, it is unclear if Sierra Nevada conifers exhibit this plasticity. Here we analysed the δ18O and δ13C values of annual tree rings to determine the water-use patterns of large Sierra Nevada conifers during the 2012–16 California drought and 4 years before this drought event (2004–07). We analysed four species (Pinus jeffreyi Grev. & Balf. (Jeffrey pine), Pinus lambertiana Dougl. (sugar pine), Abies concolor (Gord. & Glend.) Lindl. Ex Hilderbr (white fir) and Calocedrus decurrens (Torr.) Florin (incense-cedar)) across a range of topographic positions to investigate differences in water-use patterns by species and position on the landscape. We found no significant differences in δ18O and δ13C values for the pre-drought and drought periods. This stability in δ18O values suggests that trees did not shift their water-use patterns in response to the 2012–16 drought. We did find species-specific differences in water-use patterns, with incense-cedar exhibiting more depleted δ18O values than all other species. We also found trends that suggest the water source used by a tree may depend on topographic and growing environment attributes such as topographic wetness and the surrounding basal area. Overall, our results suggest that the water source used by trees varies by the species and topographic position, but that Sierra Nevada conifers do not switch their water-use patterns in response to the drought. This lack of plasticity could make Sierra Nevada conifers particularly vulnerable to drought mortality as their historically reliable water sources begin to dry out with climate change. [ABSTRACT FROM AUTHOR]

Europe witnessed a strong increase in climate variability and enhanced climate-induced extreme events, such as hot drought periods, mega heat waves, and persistent flooding and flash floods. Intensified land degradation, land use, and landcover changes further amplified the pressure on the environmental system functionalities and fuelled climate change feedbacks. On the other hand, global satellite observations detected a positive spectral greening trend—most likely as a response to rising atmospheric CO2 concentrations and global warming. But which are the engines behind such shifts in surface reflectance patterns, vegetation response to global climate changes, or anomalies in the environmental control mechanisms? This article compares long-term environmental variables (1948–2021) to recent vegetation index data (Normalized Difference Vegetation Index (NDVI), 2001–2021) and presents regional trends in climate variability and vegetation response across Europe. Results show that positive trends in vegetation response, temperature, rainfall, and soil moisture are accompanied by a strong increase in climate anomalies over large parts of Europe. Vegetation dynamics are strongly coupled to increased temperature and enhanced soil moisture during winter and the early growing season in the northern latitudes. Simultaneously, temperature, precipitation, and soil moisture anomalies are strongly increasing. Such a strong amplification in climate variability across Europe further enhances the vulnerability of vegetation cover during extreme events. [ABSTRACT FROM AUTHOR]

The study aimed to show that droughts are increasing in frequency and intensity in the Dinghushan Biosphere Reserve and to illustrate the effects of seasonal droughts on carbon gain in a subtropical forest. This is in response to the threat posed by increased droughts due to global climate change. We used four drought indices to accurately determine periods of drought and periods of increased precipitation. Thereafter, the measured eddy flux and soil moisture content data collected from 2003 to 2014 were compared between the droughts and wet periods to determine drought impacts on the ecosystem carbon gain. Drought accounted for about 20% of the 12-year study period, with the highest drought events and severity occurring between 2012 and 2013. The average annual precipitation and air temperature during the study period were 1404.57 ± 43.2 mm and 22.65 ± 0.1 °C, respectively, showing a decrease of 523 mm in precipitation and an increase of 2.55 °C in temperature, compared with the 30-year records (1990–2020). Contrary to most published data for most forest ecosystems globally, Dinghushan Biosphere Reserve recorded significant carbon gain during 60% of the drought period. [ABSTRACT FROM AUTHOR]

Sustaining agricultural productivity is essential to ensuring food security. Climate change, increasing population and dwindling resources are factors of concern threatening crop productivity. Research across the globe have focused on seeking innovative measures to protect and enhance crop yield. We explored and analyzed peer-reviewed literature to provide an understanding of current and emerging trends in the field. A bibliometric method was followed using the database Scopus. Search queries used to retrieve documents were "Agriculture/crop productivity" and "Plant stress". The study period was restricted to the last five years, from 2017-2021. The search query found 2207 documents in Scopus under the agriculture and plant stress theme. Increasing growth of publications was observed in successive years. Research activities in this field have the most contributors from Asian countries - China and India followed by the US. The major stresses affecting agricultural productivity being investigated were-Water stress, Temperature stress, Salinity stress. Amongst these, the theme related to water stress/precipitation/drought stress was the most investigated. The availability of water has a pivotal role in sustainable agriculture. The use of conservation agricultural practices such as intercropping, no-tillage, and soil mulching has proven to be effective in retaining soil water content and reducing the dependency on irrigation, especially in rainfed areas, thereby assisting in drought mitigation and increasing crop yield. Precision agriculture approach employing satellite data to predict weather and rainfall and early detection of stress signals using hyperspectral reflectance has shown promising results in ensuring sustained productivity. Breeding and transgenic approaches for plants with higher water use efficiency (WUE) and the ability to tolerate water stress are key areas of research being followed throughout the world. [ABSTRACT FROM AUTHOR]

Drought stress negatively impacts the health of long-lived trees. Understanding the genetic mechanisms that underpin response to drought stress is requisite for selecting or enhancing climate change resilience. We aimed to determine how hybrid poplars respond to prolonged and uniform exposure to drought; how responses to moderate and more severe growth-limiting drought stresses differed; and how drought responses change throughout the day. We established hybrid poplar trees (Populus × 'Okanese') from unrooted stem cutting with abundant soil moisture for 6 weeks. We then withheld water to establish well-watered, moderate and severe growth-limiting drought conditions. These conditions were maintained for 3 weeks during which growth was monitored. We then measured photosynthetic rates and transcriptomes of leaves that had developed during the drought treatments at two times of day. The moderate and severe drought treatments elicited distinct changes in growth and development, photosynthetic rates and global transcriptome profiles. Notably, the time of day of sampling produced the strongest effect in the transcriptome data. The moderate drought treatment elicited global transcriptome changes that were intermediate to the severe and well-watered treatments in the early evening but did not elicit a strong drought response in the morning. Stable drought conditions that are sufficient to limit plant growth elicit distinct transcriptional profiles depending on the degree of water limitation and on the time of day at which they are measured. There appears to be a limited number of genes and functional gene categories that are responsive to all of the tested drought conditions in this study emphasizing the complex nature of drought regulation in long-lived trees. [ABSTRACT FROM AUTHOR]

Modern forest management generally relies on thinning treatments to reduce fuels and mitigate the threat of catastrophic wildfire. They have also been proposed as a tool to augment downstream flows by reducing evapotranspiration. Warming climates are causing many forests to transition from snow-dominated to rain-dominated precipitation regimes—in which water stores are depleted earlier in the summer. However, there are relatively few studies of these systems that directly measure the hydrologic impacts of such treatments during and following snow-free winters. This work compares the below-canopy meteorological and subsurface hydrologic differences between two thinning prescriptions and an unaltered Control during periods of extreme drought and near-record precipitation (with little snow). The field site was within a coniferous forest in the rain-snow transition zone of the southern Cascades, near the Sierra Nevada Range of California. Both thinning-prescriptions had a modest and predictable impact on below-canopy meteorology, which included their causing lower nighttime minimum temperatures in the critical summer months and higher wind speeds. Relative to the Control, both treatments affected soil moisture storage by delaying its annual decline and increasing its minimum value by the end of the season. The onset of soil moisture depletion was strongly tied to the magnitude of winter precipitation. In dry years, it began much earlier within the dense Control stand than in the treated ones, and, without snow, soil moisture was not replenished in the late spring. During high precipitation years, the storage capacity was topped off for all three stands, which resulted in similar timing of moisture decline across them, later in the season. The two thinning prescriptions increased stores through the height of summer (in wet and drought years). Finally, the basal area increment (BAI) of the remaining trees rose in both, suggesting they used the excess moisture to support rapid growth.

Drought is a major natural hazard with far-reaching social, economic, and environmental impacts whose characteristics are highly interdependent across different spatial and temporal scales. Traditional global warming impact assessments on drought at the global scale have, however, taken into account only one drought characteristic at a time, likely leading to an underestimation of the overall impact. Here, we perform a trivariate analysis of changes in drought conditions at 1.5°, 2°, and 3°C global warming levels using 25 CMIP6 GCMs. Drought properties are characterized by the Standardized Soil Moisture Index (SSI). The future joint return periods of droughts historically associated with 10-, 20-, and 30-yr return periods are computed under the warming levels using copula functions considering drought duration, peak, and severity. Our comparative assessments of global warming impact on drought properties between univariate and trivariate analyses corroborate the substantial underestimation of the impact by the univariate analysis. The trivariate analysis shows that around 63%–91% of the global land will be subject to more recurrent droughts, while the percentage of the land reduces to 41%–56% for the univariate analysis. The difference between the univariate and trivariate analyses enlarges with global warming levels and the extremity of drought events. Based on the trivariate analysis, a 30-yr drought would become at least threefold more recurrent in 11%, 15%, and 20% of the global land at 1.5°, 2°, and 3°C warming levels, respectively, but the univariate analysis could not reach such large increases in drought conditions. [ABSTRACT FROM AUTHOR]

Dirre Sheikh Hussein is a religious complex in Ethiopia that dates from the 12th century or earlier. An important focus for pilgrimage, it lies in an isolated part of Oromia State on poorly drained semi-arid lowlands. Significant architecturally and culturally, recent expansion and refurbishment of the major buildings led to structural issues, though these are now largely overcome through consolidation of the prayer hall roof, laying a stone walkway, digging drainage ditches etc. Current deterioration of the buildings can be seen as: (i) fading of colours, (ii) cracks in walls, roofs, and festive places, (iii) deposits of sand around walls and (iv) staining and drainage marks on the white painted surfaces. Heavy falls of rain overwhelm drainage and overfill storage pools. Meteorological observations are infrequent locally, so those made some 70–100 km away were used, along with regridded historical data, reanalysis and CMIP6 projections. These revealed increases in temperature, precipitation and humidity, and provided indications of long-term climate pressures at the site. Changing patterns of future precipitation, particularly heavy rain, may threaten the site. The relative humidity changes are small, though an increasing Scheffer index suggests potentially enhanced wood decay. Changes in soil moisture have the potential to disrupt the foundations. Very hot days may become a problem for the two annual celebrations at the site. [ABSTRACT FROM AUTHOR]

Earth System Models' complex land components simulate a patchwork of increases and decreases in surface water availability when driven by projected future climate changes. Yet, commonly‐used simple theories for surface water availability, such as the Aridity Index (P/E0) and Palmer Drought Severity Index (PDSI), obtain severe, globally dominant drying when driven by those same climate changes, leading to disagreement among published studies. In this work, we use a common modeling framework to show that Earth System Model (ESM) simulated runoff‐ratio and soil‐moisture responses become much more consistent with the P/E0 and PDSI responses when several previously known factors that the latter do not account for are cut out of the simulations. This reconciles the disagreement and makes the full ESM responses more understandable. For ESM runoff ratio, the most important factor causing the more positive global response compared to P/E0 is the concentration of precipitation in time with greenhouse warming. For ESM soil moisture, the most important factor causing the more positive global response compared to PDSI is the effect of increasing carbon dioxide on plant physiology, which also drives most of the spatial variation in the runoff ratio enhancement. The effect of increasing vapor‐pressure deficit on plant physiology is a key secondary factor for both. Future work will assess the utility of both the ESMs and the simple indices for understanding observed, historical trends. Plain Language Summary: Rivers and groundwater provide almost all water used by humans, and soil moisture is critical for vegetation and crops worldwide. Supercomputer model simulations of rivers, groundwater and soil moisture under future global warming routinely project that some world regions will experience increases in the availability of these resources, while others will experience decreases. Yet the simple formulas that scientists have traditionally relied on to measure climatic "drought" and "aridity" obtain large future decreases in water availability (drying) almost everywhere. This has led to confusion in prior studies and reports. In this study, we resolve this apparent paradox by pinpointing exactly why the supercomputer simulations are less pessimistic than the simple formulas. For rivers and groundwater, the most important reason is that precipitation gets "flashier" and more intense with global warming. For soil moisture, the most important reason is that increasing carbon dioxide allows vegetation to use less water, keeping more water in the soil. Both of these processes are included in the computer models, but not in the simple formulas. This new understanding gives us greater confidence that the computer models are behaving reasonably. Key Points: Community Land Model 5 runoff ratio and soil moisture responses to climate change closely follow the Aridity Index (P/E0) and Palmer Drought Severity Index (PDSI) in a simplified simulationRunoff ratio increases much more than P/E0 in full simulations primarily due to changes in the temporal pattern of precipitationSoil moisture increases more than PDSI in full simulations primarily due to CO2 and vapor pressure deficit effects on plant physiology [ABSTRACT FROM AUTHOR]

Soils support a diverse range of organic life and provide several ecosystem functions and services that allow terrestrial life to thrive. Earthworms influence greenhouse gas (GHG) emissions from the soil both biologically (via respiration and litter modification) and physically (via increased macroporosity and altered air and water movement pathways). They improve soil carbon sequestration but also actively contribute to the release of major greenhouse gases. Shifting geographical ranges of earthworms due to changes in climatic conditions might affect the composition, structure and function of the soil ecosystem. This review examines the possible effects of the projected change in climate on earthworm communities and resulting implications for soil GHGs due to changes in environmental endpoints such as temperature and moisture. Earthworm activity, abundance, and biomass increase as soil moisture content increases, but drought and flooding reduce earthworm productivity. Climate change is likely to exacerbate earthworm invasions at higher latitudes and altitudes. However, because higher temperatures inhibit earthworm activities during droughts, anticipated warmer and drier climates may impede earthworm invasions. Climate change may disrupt the delicate balance between carbon sequestration and greenhouse gas emissions from soil in the coming century, but there are currently insufficient field studies to back up these prognostications. [ABSTRACT FROM AUTHOR]

Abstract Earth System Models’ complex land components simulate a patchwork of increases and decreases in surface water availability when driven by projected future climate changes. Yet, commonly‐used simple theories for surface water availability, such as the Aridity Index (P/E0) and Palmer Drought Severity Index (PDSI), obtain severe, globally dominant drying when driven by those same climate changes, leading to disagreement among published studies. In this work, we use a common modeling framework to show that Earth System Model (ESM) simulated runoff‐ratio and soil‐moisture responses become much more consistent with the P/E0 and PDSI responses when several previously known factors that the latter do not account for are cut out of the simulations. This reconciles the disagreement and makes the full ESM responses more understandable. For ESM runoff ratio, the most important factor causing the more positive global response compared to P/E0 is the concentration of precipitation in time with greenhouse warming. For ESM soil moisture, the most important factor causing the more positive global response compared to PDSI is the effect of increasing carbon dioxide on plant physiology, which also drives most of the spatial variation in the runoff ratio enhancement. The effect of increasing vapor‐pressure deficit on plant physiology is a key secondary factor for both. Future work will assess the utility of both the ESMs and the simple indices for understanding observed, historical trends.

Background and Aims Foliar water uptake has recently been suggested as a possible mechanism for the restoration of hydraulically dysfunctional xylem vessels. In this paper we used a combination of ecophysiological measurements, X-ray microcomputed tomography and cryo-scanning electron microscopy during a drought treatment to fully evaluate this hypothesis. Key Results Based on an assessment of these methods in beech (Fagus sylvatica L.) seedlings we were able to (1) confirm an increase in the amount of hydraulically redistributed water absorbed by leaves when the soil water potential decreased, and (2) locate this redistributed water in hydraulically active vessels in the stem. However, (3) no embolism repair was observed irrespective of the organ under investigation (i.e. stem, petiole or leaf) or the intensity of drought. Conclusions Our data provide evidence for a hydraulic pathway from the leaf surface to the stem xylem following a water potential gradient, but this pathway exists only in functional vessels and does not play a role in embolism repair for beech. [ABSTRACT FROM AUTHOR]

Variability in hydroclimate impacts natural and human systems worldwide. In particular, both decadal variability and extreme precipitation events have substantial effects and are anticipated to be strongly influenced by climate change. From a practical perspective, these impacts will be felt relative to the continuously evolving background climate. Removing the underlying forced trend is therefore necessary to assess the relative impacts, but to date, the small size of most climate model ensembles has made it difficult to do this. Here we use an archive of large ensembles run under a high-emissions scenario to determine how decadal “megadrought” and “megapluvial” events—and shorter-term precipitation extremes—will vary relative to that changing baseline. When the trend is retained, mean state changes dominate: In fact, soil moisture changes are so large in some regions that conditions that would be considered a megadrought or pluvial event today are projected to become average. Time-of-emergence calculations suggest that in some regions including Europe and western North America, this shift may have already taken place and could be imminent elsewhere: Emergence of drought/pluvial conditions occurs over 61% of the global land surface (excluding Antarctica) by 2080. Relative to the changing baseline, megadrought/megapluvial risk either will not change or is slightly reduced. However, the increased frequency and intensity of both extreme wet and dry precipitation events will likely present adaptation challenges beyond anything currently experienced. In many regions, resilience against future hazards will require adapting to an ever-changing “normal,” characterized by unprecedented aridification/wetting punctuated by more severe extremes. [ABSTRACT FROM AUTHOR]

This work is on development to an efficient and affordable watering system. An automatic plant watering system using Arduino microcontroller UNO R3 is programmed such that it interrupts the signals to the motor. Soil sensor is connected to the pin to the Arduino board which senses the moisture content present in the soil. Whenever the soil moisture content goes down, the sensor senses the humidity change and instructs the microcontroller so that pump can be activated, thus reducing water wastage. Global warming in nowadays is a serious issue. As the temperatures are rising, there is an observable change in the climatic conditions that is not usually found in the region. With the rising sea levels, many part of the world suffer with either severe famine/drought or floods. Due to this unpredictability of water resources, the farmers are unable to get good yields or may spoil the yield by watering the crops more than required. Hence, we intend to find an economical solution by developing a cost-efficient watering system that has the capability of sensing the moisture content in the soil and water them, if needed. [ABSTRACT FROM AUTHOR]

Drought is projected to become more severe and widespread as global warming continues in the twenty-first century, but hydroclimatic changes and their drivers are not well examined in the latest projections from phase 6 of the Coupled Model Intercomparison Project (CMIP6). Here, precipitation (P), evapotranspiration (E), soil moisture (SM), and runoff (R) from 25 CMIP6 models, together with self-calibrated Palmer drought severity index with Penman–Monteith potential evapotranspiration (scPDSIpm), are analyzed to quantify hydroclimatic and drought changes in the twenty-first century and the underlying causes. Results confirm consistent drying in these hydroclimatic metrics across most of the Americas (including the Amazon), Europe and the Mediterranean region, southern Africa, and Australia, although the drying magnitude differs, with the drying being more severe and widespread in surface SM than in total SM. Global drought frequency based on surface SM and scPDSIpm increases by ∼25%–100% (50%–200%) under the SSP2-4.5 (SSP5-8.5) scenario in the twenty-first century together with large increases in drought duration and areas, which result from a decrease in the mean and flattening of the probability distribution functions of SM and scPDSIpm, while the R-based drought changes are relatively small. Changes in both P and E contribute to the SM change, whereas scPDSIpm decreases result from ubiquitous PET increases and P decreases over subtropical areas. The R changes are determined primarily by P changes, while the PET change explains most of the E increase. Intermodel spreads in surface SM and R changes are large, leading to large uncertainties in the drought projections. SIGNIFICANCE STATEMENT: Drought may become more severe and widespread under greenhouse gas (GHG)-induced global warming in the twenty-first century based on model projections. However, there are still large uncertainties in projected future drought changes, especially regarding the extent to which drought changes depend on drought indices and the future emissions scenarios analyzed. The latest projections from CMIP6 models reaffirm the widespread drying and increases in agricultural drought by up to 200% over most of the Americas (including the Amazon), Europe and the Mediterranean region, southern Africa, Southeast Asia, and Australia under moderate-to-high emissions scenarios in the twenty-first century, despite large uncertainties in individual projections partly due to internal variability. Ubiquitous increases in atmospheric demand for moisture under rising temperatures and precipitation decreases over many subtropical regions are the main driver of the projected drying and drought increases. [ABSTRACT FROM AUTHOR]

The literature on belief regarding climate is extensive, with results showing that both personal characteristics and personal experience with the effects of climate change strongly influence future expectations. The vast majority of studies rely on cross-sectional data, making it difficult to ascertain the durability of expectations regarding future climate or the effect of additional environmental cues on beliefs. A few panel studies of which we are aware exploit extreme weather events to find evidence of "confirmation bias", in which additional environmental signalling reinforces existing beliefs. In contrast, we evaluate how normal fluctuations in soil moisture causally impact expectations of future drought using a panel of New Zealand farmers. We find that environmental cues such as soil moisture scarcely affect expectations of respondents who already expected future drought to increase but that soil moisture strongly influences respondents who did not. In particular, drier soils are associated with higher expectations of future drought among these former sceptics, whether they previously believed that future drought would decrease or simply would not change. Thus, as New Zealand moves toward IPCC forecasts of more frequent and more severe drought, farmers, foresters, and growers will increasingly agree with the scientific consensus, raising the likelihood of both farm-level and public action. [ABSTRACT FROM AUTHOR]

Soil respiration (Rs) is the second-largest terrestrial carbon (C) flux. Although Rs has been extensively studied across a broad range of biomes, there is surprisingly little consensus on how the spatiotemporal patterns of Rs will be altered in a warming climate with changing precipitation regimes. Here, we present a global synthesis Rs data from studies that have manipulated precipitation in the field by collating studies from 113 increased precipitation treatments, 91 decreased precipitation treatments, and 14 prolonged drought treatments. Our meta-analysis indicated that when the increased precipitation treatments were normalized to 28% above the ambient level, the soil moisture, Rs, and the temperature sensitivity (Q10) values increased by an average of 17%, 16%, and 6%, respectively, and the soil temperature decreased by -1.3%. The greatest increases in Rs and Q10 were observed in arid areas, and the stimulation rates decreased with increases in climate humidity. When the decreased precipitation treatments were normalized to 28% below the ambient level, the soil moisture and Rs values decreased by an average of -14% and -17%, respectively, and the soil temperature and Q10 values were not altered. The reductions in soil moisture tended to be greater in more humid areas. Prolonged drought without alterations in the amount of precipitation reduced the soil moisture and Rs by -12% and -6%, respectively, but did not alter Q10. Overall, our synthesis suggests that soil moisture and Rs tend to be more sensitive to increased precipitation in more arid areas and more responsive to decreased precipitation in more humid areas. The responses of Rs and Q10 were predominantly driven by precipitation-induced changes in the soil moisture, whereas changes in the soil temperature had limited impacts. Finally, our synthesis of prolonged drought experiments also emphasizes the importance of the timing and frequency of precipitation events on ecosystem C cycles. Given these findings, we urge future studies to focus on manipulating the frequency, intensity, and seasonality of precipitation with an aim to improving our ability to predict and model feedback between Rs and climate change.

This study examined the hydrological/meteorological controls on largewildfires > 10,000 acres (40.5 km²) during 2017-2020 in Northern California at spatial and temporal scales of the target wildfires' occurrence or growth. This study used the following simple indices for analysis: Moisture Deficit Index (MDI) computed by dividing vapor pressure deficit by soil moisture, MDIWIND computed by multiplying MDI by horizontal wind speed, and MDIGUST computed by multiplying MDI by wind gust speed. The ignition location MDIWIND and MDIGUST showed larger values on the ignition date in fire-years compared to non-fire-years for most of the target wildfires (95.8% and 91.7%, respectively). The peak timing of MDIGUST, which is to evaluate the integrated effect of dry atmosphere/soil and windy condition, coincided with the ignition date for August Complex Fire 2020, Ranch Fire 2018, Claremont-Bear Fire 2020, and Camp Fire 2018. We also found that August Complex Fire 2020, Claremont-Bear Fire 2020, and Camp Fire 2018 occurred in the areas where MDIGUST became spatially and temporally high. Further, strong relationships were found between burned area sizes of the target wildfires and MDI (R = 0.62, p = 0.002), MDIWIND (R = 0.72, p < 0.001), and MDIGUST (R = 0.68, p < 0.001). Overall, the findings in this study implied the strong effect of dry atmosphere/soil and windy conditions on recent large wildfire activities in Northern California. The findings could contribute to a more temporally and spatially detailed forecast of wildfire risks or a better understanding of wildfires' occurrence and growth mechanisms. [ABSTRACT FROM AUTHOR]

Motivated by the uncommon yet highly impactful co‐occurrence of California (CA) drought and a northeast Pacific (NEP) marine heatwave (MHW) during 2013–2016, we examined such compound extremes in Coupled Model Intercomparison Project Phase 6 projections, comparing the end of the 21st century with the preindustrial period, and separating effects of long‐term trends from interannual variability. Here, we show that long‐term trends due to anthropogenic climate change will dramatically increase the co‐occurrence of extreme dry CA and warm NEP conditions. When trends are removed, the co‐occurrence of CA drought and Gulf of Alaska (GOA) MHW will increase while the co‐occurrence of CA drought and California Current (CC) MHW remains unchanged. A stronger link between GOA MHW and subsequent CC MHW as well as decreased persistence in CA drought are also projected under anthropogenic warming. These frequency changes are consistent with shifts in distributions of sea surface temperature and soil moisture anomalies associated with individual extremes. Plain Language Summary: From 2013 to 2016, an exceptional California drought co‐occurred with extreme northeast Pacific (NEP) marine heatwaves (MHWs), leading to significant social‐economical‐ecological impacts. The evolution of this event led us to examine California drought co‐occurring with MHWs in the California Current (CC) and in the Gulf of Alaska (GOA), as well as other relevant sequential events. To distinguish effects of long‐term trends from year‐to‐year variability, we separately examine frequency changes in event occurrence with and without trends. Here, we show that under global warming, co‐occurrence of extreme warm NEP ocean and dry California conditions will become dramatically more frequent by the end of the 21st century. This increasing frequency of co‐occurrence is strongly driven by anthropogenic warming and drying trends. If these trends are removed, co‐occurrence between GOA MHWs and California drought will increase, but co‐occurrence of CC NHWs and California drought remains unchanged relative to cases with no warming. We also found stronger links between MHWs in the GOA and subsequent MHWs in the CC, and reduced frequency of persistent California droughts. Understanding changes not just in extremes but in their co‐occurrence is critical to projecting the future impacts of multiple ecosystem stressors. Key Points: Anthropogenic warming will increase the co‐occurrence of extreme warm northeast Pacific and dry California conditionsControlling for trends, California drought co‐occurs more frequently with marine heatwaves in the Gulf of Alaska but not in the California CurrentShifts in distributions of associated sea surface temperature and soil moisture anomalies are consistent with changes in co‐occurrences [ABSTRACT FROM AUTHOR]

Future changes to the hydrological cycle are projected in a warming world, and any shifts in drought risk may prove extremely consequential for natural and human systems. In addition to long‐term moistening, drying, or warming trends, perturbations to the annual cycle of regional hydroclimate variables may also have substantial impacts. We analyze projected changes in several hydroclimate variables across the continental United States, along with shifts in the amplitude and phase of their annual cycles. We find that even in regions where no robust change in the annual mean is expected, coherent changes to the annual cycle are projected. In particular, we identify robust regional phase shifts toward earlier arrival of peak evaporation in the northern regions, and peak runoff and total soil moisture in the western regions. Changes in the amplitude of the annual cycle of total and surface soil moisture are also projected, and reflect changes to the annual cycle in surface water supply and demand. Whether changes become detectable above the background noise of internal variability depends strongly on the future scenario considered, and significant changes to the annual cycle are largely avoided in the lowest‐forcing scenario. Plain Language Summary: State‐of‐the‐art climate models project substantial changes to the climate of the continental United States (CONUS). Models project changes to the yearly average rainfall, soil moisture, and runoff in many regions. But crucially, they also project changes to the annual cycle, with peaks in evaporation, runoff, and soil moisture projected to shift earlier in the year even if the yearly averages of those quantities do not change. While different climate models disagree on the exact nature of many shifts, a large source of uncertainty is human behavior and policy choices, and many significant changes can be avoided if greenhouse gas emissions fall drastically in the future. Key Points: Coupled Model Intercomparison Project models project changes to the annual cycle of many hydroclimate variables, many of which are more significant than annual mean changesIn the continental United States, there are significant earlier shifts in the annual cycle in a high emissions scenarioSignificant changes to the annual cycle are largely avoided in the lowest‐emissions scenario [ABSTRACT FROM AUTHOR]

Over the last two decades, southwestern North America (SWNA) has been in the grip of one of the most severe droughts of the last 1,200 years, with one third to nearly one half of its severity attributable to climate change. We analyze how the risk of extreme soil moisture droughts in SWNA, analogous to the most severe 21‐year (≥ in magnitude to 2000–2020) and single‐year (≥ in magnitude to 2002) events of the last several decades, changes in projections from Phase 6 of the Coupled Model Intercomparison Project. By the end of the 21st century, SWNA experiences robust (R ≥ 0.80) soil moisture drying and substantial increases in extreme single‐year drought risk that scale strongly with warming, spanning an 8%–26% probability of occurrence across +2–4 K. Notably, our results show that 21‐year droughts analogous to 2000–2020 are up to 5 times more likely than extreme single‐year droughts under all levels of warming (≈50%). These high levels of 21‐year drought risk are largely invariant across scenarios because of large spring precipitation declines in half the models, shifting SWNA into a drier mean state. Despite projections of this sweeping and ostensibly inevitable increase in 21‐year drought risk, climate mitigation reduces their severity by reducing the magnitude of extreme single‐year droughts during these events. Our results emphasize both the importance of preparing SWNA for imminent increases in persistent drought events and constraining projected precipitation uncertainty to better resolve future long‐term drought risk. Plain Language Summary: Drought is an important natural hazard in southwestern North America, and there is strong evidence that climate change is already increasing the severity of droughts in the region. Using the latest, state‐of‐the‐art climate change projections, we find that warming in the future will increase the risk of both extreme single‐year and 21‐year soil moisture droughts that are similar to major events of the last two decades. Furthermore, we show that while the magnitude of warming has a strong influence on single‐year droughts, even modest warming is likely to lock in an approximately 50% chance of a 21‐year drought similar to 2000–2020 by the end of the 21st century. The high levels of 21‐year drought risk are driven by large precipitation declines in half the models, which shift the region to a drier mean state under even the lowest warming scenario. Despite the apparent insensitivity of 21‐year drought risk to mitigation measures, our results still demonstrate the value of climate change mitigation for reducing future drought severity and single‐year extreme drought risk in the region. Our study also highlights the importance of precipitation responses in the models as major uncertainties that must be resolved to increase our confidence in these projections. Key Points: Models project higher risk of soil moisture droughts like the recent event in southwestern North America by 2100Climate mitigation minimally reduces 21‐year drought risk because half the ensemble projects large precipitation declines in all scenariosMitigation reduces the magnitude of extreme single‐year droughts, even during longer events, making high‐risk droughts less severe [ABSTRACT FROM AUTHOR]

The response of trees to intra‐annual environmental constraints varies temporally throughout a growing season and spatially across landscapes. A better understanding of these dynamics will help us anticipate the impacts of short‐term climate variability and medium‐term climate change on forests. Using the process‐based 3‐PG forest ecosystem model, we assessed the spatial manifestation and seasonal variation in environmental constraints [vapour pressure deficit (VPD), air temperature and soil water availability] on tree growth for the potential distribution range of seven widespread Central European tree species.We focused our analyses on Switzerland, where large climatic gradients occur within a comparatively small geographic area. On average, over the last 60 years, simulated forest growth during the May–August growing season was limited by high VPD (67% of the forested area), low air temperature (29%) or low soil water availability (4%). But this response varied among species and across elevations.When comparing the period 1961–1990 with 1991–2018, we observed major shifts from former temperature limitation to recent VPD limitation across 12% of the area (3%–25%, depending on species), mainly at mid‐elevations (700–1,200 m a.s.l.). At the same time, forest growth at lower elevations (i.e. below 700 m a.s.l.) became more limited by available soil water at the end of the growing season.Synthesis. Our results highlight how the relative impact of environmental growth constraints has shifted in the last three decades, and show that the importance of VPD as a dominant environmental growth constraint has increased for tree species in Swiss and Central European forests. Understanding the spatial and temporal variability in environmental growth constraints will help to generate accurate species‐specific risk maps for forest managers to identify areas with elevated drought and heat stress in the near future. [ABSTRACT FROM AUTHOR]

Global climate change is predicted to increase the frequency of droughts, with major impacts on tropical savannas. It has been suggested that during drought, increased soil moisture and nutrients on termite mounds could benefit plants but it is unclear how such benefits could cascade to affect insect communities.Here, we describe the effects of drought on vegetation structure, the cascading implications for invertebrates and how termite mounds influence such effects. We compared how changes in grass biomass affected grasshopper and ant diversity on and off Macrotermes mounds before (2012) and during a drought (2016) at two locations that experienced large variation in drought severity (Skukuza and Pretoriuskop) in the Kruger National Park, South Africa.The 2013–2016 drought was not ubiquitous across the study site, with rainfall decreasing at Skukuza and being above average at Pretoriuskop. However, grass biomass declined at both locations. Grasshopper abundance decreased at droughted Skukuza both on and off mounds but decreased on mounds and increased off mounds at non‐droughted Pretoriuskop. Ant abundance and species richness increased at Skukuza but remained the same on mounds and decreased off mounds at Pretoriuskop.Our results demonstrate the spatially extensive effects of drought. Despite above average rainfall in 2016 at Pretoriuskop, grass biomass decreased, likely due to an influx of large mammalian herbivores from drought‐affected areas. This decrease in grass biomass cascaded to affect grasshoppers and ants, further illustrating the effects of drought on invertebrates in adjoining areas with higher rainfall. Our grasshopper results also suggest that increased drought in savannas will contribute to overall declines in insect abundance. Moreover, our recorded increase in ant abundance was primarily in the form of increases in dominant species, illustrating how drought‐induced shifts in relative abundance will likely influence ecosystem structure and function.Our study highlights the phenomenon of spill‐over drought effects and suggests rather than mitigating drought, termite mounds can instead become the focus for more intense grazing, with important consequences for insect communities. [ABSTRACT FROM AUTHOR]

Recruitment for many arid‐zone plant species is expected to be impacted by the projected increase in soil temperature and prolonged droughts associated with global climate change. As seed dormancy is considered a strategy to avoid unfavorable conditions, understanding the mechanisms underpinning vulnerability to these factors is critical for plant recruitment in intact communities, as well as for restoration efforts in arid ecosystems. This study determined the effects of temperature and water stress on recruitment processes in six grass species in the genus Triodia R.Br. from the Australian arid zone. Experiments in controlled environments were conducted on dormant and less‐dormant seeds at constant temperatures of 25°C, 30°C, 35°C, and 40°C, under well‐watered (Ψsoil = −0.15 MPa) and water‐limited (Ψsoil = −0.35 MPa) conditions. Success at three key recruitment stages—seed germination, emergence, and survival—and final seed viability of ungerminated seeds was assessed. For all species, less‐dormant seeds germinated to higher proportions under all conditions; however, subsequent seedling emergence and survival were higher in the more dormant seed treatment. An increase in temperature (35–40°C) under water‐limited conditions caused 95%–100% recruitment failure, regardless of the dormancy state. Ungerminated seeds maintained viability in dry soil; however, when exposed to warm (30–40°C) and well‐watered conditions, loss of viability was greater from the less‐dormant seeds across all species. This work demonstrates that the transition from seed to established seedling is highly vulnerable to microclimatic constraints and represents a critical filter for plant recruitment in the arid zone. As we demonstrate temperature and water stress‐driven mortality between seeds and established seedlings, understanding how these factors influence recruitment in other arid‐zone species should be a high priority consideration for management actions to mitigate the impacts of global change on ecosystem resilience. The knowledge gained from these outcomes must be actively incorporated into restoration initiatives. [ABSTRACT FROM AUTHOR]

Predicting the impacts of projected change in precipitation (P) and temperature (T) on occurrence of drought and extreme events is essential for managing natural resources and setting policy. This study compares future occurrence of excessively dry and wet periods based on P, T, stream flow, soil moisture, and extreme P and T events. The comparisons are based on coupled future climate projections from multiple Earth system models downscaled using site-specific weather data and hydrologic model outputs for the Goodwater Creek Experimental Watershed, Missouri, USA. The use of multiple drought indices, downscaled climate data, and process model output facilitated drought prediction for different land surface processes and its comparison. The P and T extremes and droughts were calculated using standardized indices. The results based on drought and extreme indices indicate increased frequency and duration of drought in the future, primarily due to a projected decline in summer precipitation resulting in summer droughts. The streamflow and soil water-based drought indices indicated increased spring drought risks in the future despite a precipitation increase, indicating the importance of process representation with hydrologic models for drought computation. [ABSTRACT FROM AUTHOR]

To develop measures to reduce the vulnerability of forests to drought, it is necessary to estimate specific water balances in sites and to estimate their development with climate change scenarios. We quantified the water balance of seven forest monitoring sites in northeast Germany for the historical time period 1961–2019, and for climate change projections for the time period 2010–2100. We used the LWF-BROOK90 hydrological model forced with historical data, and bias-adjusted data from two models of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) downscaled with regional climate models under the representative concentration pathways (RCPs) 2.6 and 8.5. Site-specific monitoring data were used to give a realistic model input and to calibrate and validate the model. The results revealed significant trends (evapotranspiration, dry days (actual/potential transpiration < 0.7)) toward drier conditions within the historical time period and demonstrate the extreme conditions of 2018 and 2019. Under RCP8.5, both models simulate an increase in evapotranspiration and dry days. The response of precipitation to climate change is ambiguous, with increasing precipitation with one model. Under RCP2.6, both models do not reveal an increase in drought in 2071–2100 compared to 1990–2019. The current temperature increase fits RCP8.5 simulations, suggesting that this scenario is more realistic than RCP2.6. [ABSTRACT FROM AUTHOR]