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The mid-Piacenzian Warm Period (MPWP, ~ 3.264–3.025 Ma) is the most recent example of a persistently warmer climate in equilibrium with atmospheric CO2 concentrations similar to today. Towards studying patterns and dynamics of a warming climate the MPWP is often compared to today. Following the Pliocene Model Intercomparison Project, Phase 2 (PlioMIP2) protocol we prepare a water isotope-enabled Community Earth System Model (iCESM1.2) simulation that is warmer and wetter than the PlioMIP2 multi-model ensemble (MME). While our simulation resembles PlioMIP2 MME in many aspects we find added insights. (1) Considerable warmth at high latitudes exceeds previous simulations. Polar amplification (PA) is comparable to proxies, enabled by iCESM1.2's high climate sensitivity and a distinct method of ocean initialization. (2) Major driver of warmth is the downward component of clear-sky surface long-wave radiation ( Δ T rlds _ clearsky ). (3) In iCESM1.2 modulated dominance of dynamic (δDY) processes causes different low-latitude (~ 30 S°–10°N) precipitation response than the PlioMIP2 MME, where thermodynamic processes (δTH) dominate. (4) Modulated local condensation leads to lower δ18Op across tropical Indian Ocean and surrounding Asian-African-Australian monsoon regions. (5) We find contrasting changes in tropical atmospheric circulations (Hadley and Walker cells). Anomalous regional meridional (zonal) circulation, forced by changes in tropical-subtropical (tropical) diabatic processes, presents a more comprehensive perspective than explaining weakened and expanded Hadley circulation (strengthened and westward-shifted Walker circulation) via static stability. (6) Enhanced Atlantic meridional overturning circulation owes to a closed Bering Strait. [ABSTRACT FROM AUTHOR]

Monitoring areas susceptible to desertification contributes to the strategic development of regions located in environments of extreme hydric and social vulnerability. Therefore, the objective of this study is to evaluate the process of soil degradation in the Desertification Nucleus of Cabrobó (DNC) over the past three decades using remote sensing techniques. This study used primary climatic data from TerraClimate, geospatial data of land use and land cover (LULC), and vegetation indices (SAVI and LAI) via Google Earth Engine (GEE) from Landsat 5/TM and 8/OLI satellites, and established the aridity index (AI) from 1992 to 2022. The results indicated 10 predominant LULC classes with native vegetation suppression, particularly in agriculture and urbanization. SAVI ranged from −0.84 to 0.90, with high values influenced by La Niña episodes and increased rainfall; conversely, El Niño episodes worsened the rainfall regime in the DNC region. Based on the Standardized Precipitation Index (SPI), it was possible to correlate normal and severe drought events in the DNC with years under the influence of El Niño and La Niña phases. In summary, the AI images indicated that the DNC remained semi-arid and that the transition to an arid region is a cyclical and low-frequency phenomenon, occurring in specific periods and directly influenced by El Niño and La Niña phenomena. The Mann–Kendall analysis showed no increasing trend in AI, with a Tau of −0.01 and a p-value of 0.97. During the analyzed period, there was an increase in Non-Vegetated Areas, which showed a growing trend with a Tau of 0.42 in the Mann–Kendall analysis, representing exposed soil areas. Annual meteorological conditions remained within the climatic pattern of the region, with annual averages of precipitation and actual evapotranspiration (ETa) close to 450 mm and an average temperature of 24 °C, showing changes only during El Niño and La Niña events, and did not show significant increasing or decreasing trends in the Mann–Kendall analysis. [ABSTRACT FROM AUTHOR]

Understanding drought occurrence and evolution is important in minimizing the impacts associated with it. This work assesses the performance of 10 commonly used meteorological indices to measure drought in Morocco. The studied indices are Deciles Index (DI), Percent of Normal Index (PNI), Z‐Score Index (ZSI), China‐Z Index (CZI), Rainfall Anomaly Index (RAI), Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI), Palmer Drought Severity Index (PDSI), its self‐calibrated variant (scPDSI) and Palmer Z Index (PZI). Rainfall and temperature gridded data is sourced from PERSIANN‐CDR and ERA5, respectively, for the period 1983–2021. The study area exhibits three main climatic regimes; subhumid, semi‐arid and arid, with a drying and warming climate, as depicted by the rainfall and temperature trends analysis. Results show that most rainfall‐based indices perform relatively poorly in drought monitoring in the study area. DI and PNI appear to be inconsistent and abnormally responsive to rainfall. RAI reports droughts 56.5% more frequently and slightly underestimate drought intensity compared to other indices. Similarly, ZSI and CZI largely underestimate drought intensity. PDSI and scPDSI are computationally demanding, often underestimate drought intensity and overestimate drought duration by at least 115% compared to SPI and SPEI. Conversely, PZI can be used for drought onset detection as it reported droughts early compared to the other indices. SPI and SPEI perform overall better regarding their consistent drought identification and severity assessment. However, SPEI is found to be more suitable than SPI in the arid and semi‐arid regions and performed better considering the warming climate of the country. [ABSTRACT FROM AUTHOR]

Questions: How does the grass layer affect seedlings across large environmental gradients in savannas? Location: Savanna sites in Argentina, Tanzania, and South Africa. Methods: We carried out a joint analysis of three grass removal experiments in which seedlings of various Fabaceae species were transplanted into plots with native grass and companion plots where grass had been removed. First, we estimated the effect of grasses on tree seedling mortality and seedling growth rate at each site. Then, we used the resulting coefficient estimates from site‐level models to examine the impact of two climate (monthly precipitation and aridity index) and two soil (soil organic carbon content and clay content) variables on the direction and magnitude of the grass effects. Results: Grasses increased the risk of mortality, but there was no evidence for a global effect of grasses on tree seedling rate of height growth. The best model fit indicated a high mortality risk of tree seedlings in response to grasses at intermediate aridity index values. No other climate or soil variable influenced tree seedling survival or growth (monthly precipitation, soil organic carbon content and clay content). Conclusions: Our results support the notion that the grass layer consistently creates a bottleneck to tree seedling establishment in African and South American savannas beyond climate and soil conditions, mainly by affecting tree seedling survival. The negative effect of grasses on seedling survival was lower in dry conditions compared to intermediate aridity levels. These results suggest that grass–seedling interaction is less intense in drier conditions, possibly due to reduced total grass biomass, which leads to decreased site evapotranspiration and improved soil water retention capacity. [ABSTRACT FROM AUTHOR]

As an important factor that directly affects agricultural production, the social economy, and policy implementation, observed changes in dry/wet conditions have become a matter of widespread concern. However, previous research has mainly focused on the long-term linear changes of dry/wet conditions, while the detection and evolution of the non-linear trends related to dry/wet changes have received less attention. The non-linear trends of the annual aridity index, obtained by the Ensemble Empirical Mode Decomposition (EEMD) method, reveal that changes in dry/wet conditions in China are asymmetric and can be characterized by contrasting features in both time and space in China. Spatially, most areas in western China have experienced transitions from drying to wetting, while opposite changes have occurred in most areas of eastern China. Temporally, the transitions occurred earlier in western China compared to eastern China. Research into the asymmetric spatial characteristics of dry/wet conditions compensates for the inadequacies of previous studies, which focused solely on temporal evolution; at the same time, it remedies the inadequacies of traditional research on linear trends over centennial timescales. Analyzing the non-linear trend also provides for a more comprehensive understanding of the drying/wetting changes in China. [ABSTRACT FROM AUTHOR]

Flash droughts feature rapid onsets of soil moisture drought events and result in severe impacts and damages, especially on agricultural and ecological systems. How the flash drought regime across China varies on multitemporal scales with climate change is not fully clear yet. In this study, we extended the flash drought definition to apply to arid regions by adding an absolute soil moisture variation criterion. Then, we detected flash drought events across China during 1981–2021 and characterized their frequency, duration, and affected area changes on seasonal, annual, and decadal scales, using soil moisture data from the European Center for Medium-Range Weather Forecasts climate reanalysis-Land. Results show that flash drought hotspots appeared in North China and the Yangtze River Basin. During 1981–2021, the hotspots, even nationwide, underwent significant increases in frequencies, durations, and affected areas of flash droughts. The increases held in the extremely high values of the frequencies and durations in the decadal comparisons. Especially, North China saw the most extensive and rapid increases. Seasonally, flash drought frequencies and durations intensified more during spring and autumn, and seasonal hotspots in eastern China shifted in phase with spatial patterns of soil moisture loss balanced by precipitation and evapotranspiration. Thus, flash droughts tended to amplify atmospheric aridity. These findings on the hotspot regions and the spatiotemporal evolutions of flash droughts across China would pinpoint soil moisture responses to climate change and prepare for climate change impacts on local ecosystems. [ABSTRACT FROM AUTHOR]

Persistent drought events frequently intensify the aridity of ecosystems and cause catchment runoff depletion. Here, using large and long-term data sets of meteorological and hydrologic variables (precipitation, runoff, temperature, and potential evapotranspiration) investigated the major causes that modulated catchment runoff depletion between the years 1980 and 2020 in southern-central Chile. We identified the hydrological years where aridity index intensified, analyzed its relationship with annual runoff, and evaluated the effect of the annual evaporation index and annual aridity index on water balance of 44 catchments with different precipitation regimes located between 35° and 40°S. Our results showed that observed precipitation and runoff significantly decreased between 1980 and 2020 in 64% of the catchments in the study area. Potential evapotranspiration increased significantly in 39% of the catchments. Hydrological years in which precipitation decreased showed a decreased runoff trend. This result suggests that meteorological droughts tend to significantly decrease observed runoff. The runoff value decreased as the aridity index increased from 0.3 to 6.7, and the Budyko curve captured 98.5% of the annual variability of all catchments. [ABSTRACT FROM AUTHOR]

Climate change and intensified human activities are expected to alter the natural hydrological cycle would cause changes in the distribution of water resources and their availability across space and time. Therefore, the present study focused on understanding the spatiotemporal variations of hydroclimatic variables namely rainfall, surface runoff, water yield, and the Aridity Index (AI) of the Krishna River Basin (KRB) under combined impact of climate and Land Use/Land Cover (LULC) change scenarios. From trend analysis, the best model (CNRM-CM5 driven RCM) projected an increasing trend in rainfall under both RCP 4.5 and 8.5 scenarios for the entire century. Results indicated that, except for the central part, most of KRB experiences high runoff and water yield conditions under both RCP 4.5 and 8.5 scenarios in the mid and end centuries, conversely it may face low runoff and water yield conditions in the early century. Most of the central part is in arid and semi-arid conditions and, the eastern part of the basin is in dry sub-humid conditions, while the Western Ghats, Palleru, and Munneru regions of the basin fall under humid and hyper humid regions under RCP 4.5 scenario. Whereas the majority of the basin falls under humid and hyper humid regions under RCP 8.5 scenario except for the central and few other parts of the basin. In light of this, it was essential to review the current water management strategies and plan future projects to provide efficient and effective ways to mitigate the adverse impacts resulting from climate variability. [ABSTRACT FROM AUTHOR]

Climate plays a critical role in altering soil carbon (C) turnover and long‐term soil C storage by regulating water availability and temperature, and in turn biological activity. However, a systematic analysis of how key climatic factors shape the global patterns of soil C turnover is still lacking. Using global observation‐based data sets and a transit time theory, here we show that—excluding croplands and cold regions—soil C turnover time (τTO) and its variability are strongly related to ecosystem aridity through a power law scaling. According to such a relation, soil C turnover is faster but also more variable in wetter regions, suggesting more complex C cycling processes. The observed scaling of τTO and its coefficient of variation with aridity underlines the fundamental controls of climate on soil C turnover and may help reconcile soil C models with empirical observations for improved projection of soil C dynamics under climate change. Plain Language Summary: Climate regulates the metabolic activity of both plants and soil microorganisms by regulating temperature and water availability of ecosystems and, in turn, influences how fast C cycles through soils. Recent observation‐based data sets provide global estimates of both soil C age and turnover time, paving the way for novel analyses exploring how they simultaneously change across climates. Here, by analyzing these data we show that, excluding croplands and cold regions, soil C turnover time and its variability are related to ecosystem aridity through simple power laws across a broad range of aridity. Such relations reveal that, especially in wet regions, C cycling through soils is mostly young C and can consist of C with a broad range of turnover times. Our findings may help us improve the structure of soil C models and hence projections of soil C cycling under climate change. Key Points: The ratio of soil C turnover time to age shows a strong sensitivity to aridity in warm regionsSoil C turnover in warm regions is more variable under wetter conditionsThe scaling of soil C turnover time and its variability with aridity follows a self‐similar power law [ABSTRACT FROM AUTHOR]

Climate change can alter the spatial and temporal distribution of aridity around the world through a combination of factors such as reduced precipitation, rising temperatures and decreased evapotranspiration. Especially the Mediterranean region has been identified as vulnerable to anthropogenic climate change due to a significant reduction in precipitation compared to other land regions in all climate models operated under different scenarios. Despite numerous studies on aridity trends, few have focused specifically on Türkiye and considered a comprehensive range of aridity indices and scenarios. This study aims to fill this research gap by providing a more detailed understanding of future aridity trends in Türkiye under various climate change scenarios and using multiple aridity indices. A novelty of this study lies in the simultaneous examination of three aridity indices (PCI, EAI and UNEP AI) for Türkiye, allowing for a more comprehensive assessment of future aridity trends. Furthermore, this study considers three future time periods (2011–2040, 2041–2070 and 2071–2100) and three shared socioeconomic pathways (SSPs) to evaluate the potential range of climate change impacts on aridity in Türkiye. Therefore, in this study, we aimed to determine the changes in aridity conditions in Türkiye until the end of the 21st century. We used three aridity indices: the Pinna combinative index, the Erinç aridity index and the UNEP aridity index. These indices were calculated for the baseline period of 1981–2010 using gridded data (CHELSA) and for the periods of 2011–2040, 2041–2070 and 2071–2100 using three climate models (GFDL‐ESM4, MRI‐ESM2‐0 and IPSL‐CM6A‐LR) and multi‐model means with three SSPs to represent different future scenarios. The results showed that all three indices indicate an increase in dry climate conditions in Türkiye after 2041, with particularly notable increases expected in Central Anatolia, Southeastern Anatolia and parts of the Eastern Mediterranean, as well as eastern parts of Eastern Anatolia and the inner Aegean region. Under the SSP3‐7.0 scenario, the expansion of semi‐arid and arid areas is predicted to cover more than 30% of the country by the end of the century (2071–2100). This increase in aridity could increase the region's vulnerability to climate change and the risk of desertification, which should be taken into consideration in national water management and planning. [ABSTRACT FROM AUTHOR]

Numerous drylands worldwide have experienced degradation of both soil and vegetation in proximity to watering areas. Degradation can be observed in satellite imagery as fading radial brightness belts extending away from the water sources. The main objective of this study was to examine the spatio-temporal patterns of land degradation and rehabilitation in the drylands of the southeast Iberian Peninsula. The brightness index of tasseled cap was discovered to be the best form of spectral transformation for enhancing the contrast between the bright-degraded areas near the points and the darker surrounding areas far from and in between these areas. To comprehend the spatial structure present in spaceborne imagery of two desert sites and three key time periods, semi-variograms were created (mid-late 2000s, around 2015 and 2020). To assess spatio-temporal land-cover patterns, a kriging was used to smooth the brightness index values extracted from 30 m spatial resolution images. To assess the direction and intensity of changes between study periods, a change detection analysis based on kriging prediction maps was performed. These findings were linked to the socioeconomic situation prior to and following the EU economic crisis. The study discovered that degradation occurred in some areas as a result of the region's agricultural activities being exploited. [ABSTRACT FROM AUTHOR]

Formulation of the problem. Remote sensing data might be used for indirect assessment of croplands conditions and drought stress through the calculation of specific vegetation indices, such as vegetation health index (VHI), agriculture stress index (ASI), and drought intensity or weighted mean vegetation health index (WMVHI). However, the accuracy of these indices is not clear for some territories. For example, the South of Ukraine is a zone of risky agriculture, because of low natural moisture supply and high evapotranspiration. Moisture supply is the main limiting factor for sustainable crop production in this region. The goals of this study were: 1) to assess the reliability of the mentioned vegetation indices in drought assessment through the direct comparison with the UNEP aridity index; 2) to find out whether remote sensing drought indicators could be used for the yield prediction of major crops on the regional scale. Methods. The study was conducted for Kherson region of Ukraine, as it is one of the most arid regions of the country with very high drought risks. The data on average weighted annual VHI, ASI, and WMVHI for the period 1984-2022 (Season 1) were collected and generalized from the FAO Earth Observation services. UNEP aridity index was calculated using the data from Kherson regional hydrometeorological center. Correlation and linear regression analysis were performed using common statistical methodology. Results. As a result, it was found that 1) all the studied remote sensing drought indicators demonstrate poor correlation with the aridity index, therefore, they should not be used to determine meteorological drought in the region; 2) all the studied remote sensing indices, especially VHI, demonstrate moderate-to-strong correlation with the yields of certain crops, cultivated in Kherson region (R=0.54-0.86), and could be used for the yield prediction; 3) the aridity index have poor relation to the yields of major crops, cultivated in the studied area; 4) VHI-based linear regression models for the crops’ yields prediction are reliable and reasonable for scientific and practical use just for cereal crops, and are much less accurate for grain corn and sunflower; 5) based on the study findings, it could be concluded that aridity index provides pure climatological characteristics of the region, while the studied vegetation indices are mainly focused on the level of drought stress that impacts crops during the growing season. Scientific novelty and practical significance. The article provides novel insights on the implementation of remote sensing data in drought risks assessment in crop production, and their utilization for the purpose of croplands productivity prediction. The study has theoretical and practical importance for current agriculture, and the findings could be used both in scientific, educational, and practical purposes. [ABSTRACT FROM AUTHOR]

Understanding future dry and wet changes under global climate change is of great regional significance in China. Based on six Global Climate Models (GCM) from the Coupled Model Intercomparison Project phase 6 (CMIP6), we project the changes of dry‐wet climate regions in China in the 21st century under the three SSP‐RCP (shared socioeconomic pathway‐representative concentration pathway) scenarios (SSP1‐2.6, SSP2‐4.5 and SSP5‐8.5), and further identify the key climatic factors that lead to the transition of dry‐wet climate regions. The results show the area of humid and subhumid regions in China will show an upward trend in the future, while the area of semiarid and arid regions will show a downward trend. Especially under the SSP5‐8.5 scenario, the area of the subhumid region has the largest increase trend (0.042% per year), and the area of the arid region has the largest decline trend (−0.048% per year). The three main transfer directions of dry‐wet climate regions are from arid to semiarid regions, from semiarid to subhumid regions, and from subhumid to humid regions in the future. Due to the future extensive wetting trend in the north, the future dry‐wet climate regions will shift to wetter types in Tibet, North China, the Qinling‐Huaihe regions and the northeast. In addition, the key climatic factors for the transition of dry‐wet climate regions are mainly precipitation, maximum temperature and solar radiation. The increase of precipitation plays a dominant role for areas projected to change to wetter types, and the increase of potential evapotranspiration (PET) plays a dominant role for areas projected to change to drier types. The PET changes in changed areas of dry‐wet climate regions are mainly dominated by maximum temperature and solar radiation. Our research has important implications for future water resource management and reconsideration of climate mitigation and adaptation policies. [ABSTRACT FROM AUTHOR]

• AFRICLIM's bioclimatic data can be associated with plots to assess their influence on the abundance and distribution of species. • Ricinodendron heudelotii is distributed in the most watered regions of Benin. • The aridity index significantly influences the abundance of R. heudelotii. • The Yoruba-Nagot community of Benin could have considered the presence of R. heudelotii as one of the criteria for selecting a site to settle. Climate change and human activities pose a major threat to forest resources and the livelihoods of vulnerable communities. Understanding the factors that influence the distribution and abundance of priority species for these communities is crucial for conservation and sustainable management purposes. We identified the pedoclimatic and anthropogenic factors that influence the geographical distribution and abundance of Ricinodendron heudelotii , a woody species with high socio-cultural value in Benin, and assessed the demographic structure of its populations. Through a survey carried out in all phytodistricts of the Guineo-Congolian zone and the Sudano-Guinean transition zone of Benin, the species' presence was recorded with the help of the hunters and Fulani communities living in the area. We set thirty-eight plots of 1 ha (100 m× 100 m) in forests where the largest populations of the species were found. Generalized linear mixed models were used to compare the mean abundance of the species between phytodistricts and to identify underlying factors shaping observed differences. Slope analysis of the ordinary least squares regression of tree density against diameter size class distribution midpoint and the skewness coefficient were used to assess the populations' structure of the species. The species is distributed in the phytodistrict within latitude 6° 50′ - 9° 50′. These phytodistricts are the most watered phytodistricts of Benin with rainfall between 900 mm and 1300 mm per year. The abundance of the species varied from one phytodistrict to another (from 9.25 ± 2.39 to 19.5 ± 4.5 trees.ha-1) and is significantly influenced by aridity index, moisture index of the arid quarter, harvest intensity, and wildfires. An assessment of the population structure revealed a predominance of small-diameter individuals, suggesting some population stability. Long-term conservation of the species requires controlling anthropogenic pressures on its populations. [ABSTRACT FROM AUTHOR]

Renewable bioenergy has the potential to contribute sustainably to the energy sector. Forestry is the main source of biomass for energy in Europe, and poplar (genus Populus) is widely used for short rotation coppice (SRC). Many studies have assessed poplar clones’ productivity but there is a lack of regional studies and links with the climate. We investigated the biomass productivity of twenty hybrid poplar clones for SRC. Clones were planted in sixteen locations across nine countries in Europe, although not all clones were replicated in all locations. In each location, clones were planted in three replicated plots. All plots were harvested after four years, and the aboveground dry biomass estimated. We fitted clone-specific linear mixed models of total aboveground dry biomass production at plot level as function of climatic variables. For many clones (eight) only annual heat moisture deficit negatively affected productivity, in few cases (3) together with a quadratic term for a smoother relationship. In some other clones (five) only the mean summer precipitation positively and linearly affected productivity. On average, the variance explained by the fixed effects in those models was 56%. For the remaining clones (seven), no climate variables resulted significant. Our study explicitly investigated the quantitative link between water availability and poplar SRC productivity, one of the most important known factors but not often studied with a modelling approach. Further, we show the most productive clones in dried conditions. We also highlight the need to larger scale regional experiments to produce models that can be used in climate change scenarios. [ABSTRACT FROM AUTHOR]

Summary: To achieve optimal balance among wood's support, storage, and transport functions, tree species present adaptive variation in wood anatomical traits. Oaks (Quercus) are woody plants that are dominant in many ecosystems, possess wide variation in wood traits, and can tolerate water stress in diverse habitats. Mountain regions contain steep climatic gradients that exert strong environmental pressures on wood traits. The aims of this study were: (1) to quantify the anatomical variation in 21 oak species distributed along an environmental gradient and (2) to analyze the interspecific variation among the studied species. Fibres and parenchyma fractions were the most abundant cell types. We found a trade-off between total fibre fraction and total parenchyma fraction modulated by the precipitation during the warmest quarter in which oak species in drier areas invested more in support cells. The 21 oak species studied showed vasicentric tracheids, which could be essential to compensate for the transport system in drier areas. Wood density was negatively correlated with the axial parenchyma fraction and fibre lumen width. Oak species have high interspecific variation in the total vessel fraction and vessel diameter. Anatomical variation in oak species along a climatic gradient showed a broad continuum of fibre characteristics from wide to narrow wall and lumen, abundant to scarce parenchyma, and wide to narrow vessels. These variations imply a diversification of ecological strategies within the genus that includes the vascular design of the stem to define the tolerance and competitiveness of the oak species. [ABSTRACT FROM AUTHOR]

For large-scale heat waves that occur in the south of the European part of Russia (EPR), the frequency variability since the beginning of the 20th century is considered, including variations on decadal scales and a trend during the global warming period, accompanying variations in the aridity index SPI, and the structure of the longest waves. The geographic distribution of air temperature anomalies on the territory of the Russian Federation, large-scale circulation conditions, the North Atlantic sea surface temperature (SST) anomalies, which accompanied heat waves in the south of the EPR, are analyzed using the composite analysis. In particular, the wave structure was revealed of the composite field of the air temperature anomaly for days with heat waves and the related 500 hPa geopotential height () fields over Russia. The field structure generally corresponds to the negative phase of the East Atlantic–Western Russia (EAWR) circulation pattern. Similar structures of the geopotential field are observed during heat waves in the northern half of the EPR. However, in this case, there are specific features that contribute to the inflow of cold air from the north to the southern regions. It is shown that the values of the EAWR index are significantly shifted towards negative values in the months when long heat waves occur over the southern EPR. The waves are accompanied by positive anomalies of the North Atlantic SST and the strongly increased blocking anticyclone activity. The downward trend in the EAWR index observed in recent decades and the SST rise expected with the global warming increase a risk of droughts in the main grain-producing region of the country. [ABSTRACT FROM AUTHOR]

The aridity index, also known as the Budyko index, describes spatiotemporal changes in the hydroclimatic system in the long-term perspective. Defined as the ratio between potential evapotranspiration and precipitation, it can be used to determine wet (humid) and dry (arid) regions. In this study, we evaluated the aridity index estimated in different temporal scales, investigated its spatial patterns, and highlighted the long-term changes in Europe using three gridded data sets (CRU, E–OBS, and ERA5). A significant dry region expansion is evident in all data sets since the late 1980s. The extent of the dry regions has increased in Western, Central, and Eastern Europe, especially at low and medium altitudes. The results show the long-term development of the European hydroclimatic system and which areas have changed from wet to dry. [ABSTRACT FROM AUTHOR]

The sensitivity of vegetation productivity to precipitation (Sppt) is a key metric for understanding the variations in vegetation productivity under changing precipitation and predicting future changes in ecosystem functions. However, a comprehensive assessment of Sppt over all the global land is lacking. Here, we investigated spatial patterns and temporal changes of Sppt across the global land from 2001 to 2018 with multiple streams of satellite observations. We found consistent spatial patterns of Sppt with different satellite products: Sppt was highest in dry regions while low in humid regions. Grassland and shrubland showed the highest Sppt, and evergreen needle‐leaf forest and wetland showed the lowest. Temporally, Sppt showed a generally declining trend over the past two decades (p <.05), yet with clear spatial heterogeneities. The decline in Sppt was especially noticeable in North America and Europe, likely due to the increase in precipitation. In central Russia and Australia, however, Sppt showed an increasing trend. Biome‐wise, most ecosystem types exhibited significant decrease in Sppt, while grassland, evergreen broadleaf forest, and mixed forest showed slight increases or non‐significant changes in Sppt. Our finding of the overall decline in Sppt implies a potential stabilization mechanism for ecosystem productivity under climate change. However, the revealed Sppt increase for some regions and ecosystem types, in particular global grasslands, suggests that grasslands might be increasingly vulnerable to climatic variability with continuing global climate change. [ABSTRACT FROM AUTHOR]

Land-atmosphere coupling is a key factor for understanding the mean hydroclimatological conditions in South America. In this study, we analyzed how land-atmosphere coupling modulates the aridity conditions in the South American continent through experiments performed with a regional climate model. We assessed changes in precipitation (P), potential evaporation (PET), aridity index (ɸ = PET / P) and vapor pressure deficit (VPD) in experiments with and without soil moisture - atmosphere coupling. Additionally, we analyzed how air dry enthalpy (Hd), moist enthalpy (Hw) and total enthalpy (Ht) change between the coupled and uncoupled experiments, which help to identify patterns in aridity conditions. When analyzing ɸ, we found opposite responses in central-eastern Brazil and southeastern South America (SESA), the two main hotspots of land-atmosphere coupling. On the other hand, a widespread amplification of VPD is found. Both VPD and enthalpy are locally driven by changes in temperature and water vapor content and reflect wetter conditions in central-eastern Brazil and drier conditions in SESA. Changes in regional circulation, described in previous studies, increase moisture convergence in Brazil and help to explain the response of each individual metric when coupling is enabled. [ABSTRACT FROM AUTHOR]

[Display omitted] • Change in rainfall is more prominent in summer and post-summer seasons. • There is an increment in the loss of water in the watersheds through evapotranspiration. • Seasonal aridity is likely to increase on the source of the Blue Nile. Evapotranspiration is one of the determinant components of the hydrological process, highly influenced by climate change due to the increase in atmospheric temperature at global and regional scales. This study was designed to evaluate the extent to which climate change affects the Potential Evapotranspiration (PET) and the consequent Aridity Index (AI) in the high-emission scenario of Representative Concentration Pathways (RCPs) in the Gilgel Abay, Ribb, Gumara, and Megech watersheds using six Global Climate Models in the 2011–2040, 2041–2070, and 2071–2100 relative to the 1971–2000 (baseline period). The average PET is simulated using the Soil Water Assessment Tool (SWAT) model. Penman-Monteith and Hargreaves methods were used in the computation of PET using the water balance technique, and the Hargreaves method was found more efficient in calibration and validation processes. The Aridity Index (AI) of watersheds is calculated using the ratio of precipitation and potential evapotranspiration. The study revealed that the change in annual average PET is showing an increasing pattern in the three time periods, and the highest rate of changes in Megech, Gilgel Abay, Ribb, and Gumara, watersheds are 16.66%, 15.53%, 14.68%, and 13.46%, respectively in the 2071–2100 time period. Seasonally, the highest rate of change in PET is 20.37% (September), 19.29% (April), 17.46% (March), and 17.02% (March) in the Megech, Gilgel Abay, Ribb, and Gumara, respectively. Similarly, the seasonal highest change in Aridity Index (AI) is also likely to be observed in the 2071–2100 in which in the dry season, it accounts –0.303 (March), –0.299 (March), –0.285 (April), and –0.276 (April) in the Ribb, Gumara, Gilgel Abay, and Megech, respectively, whereas in the rainy season, the change is 0.263, 0.258, 0.238, and 0.211 in the Gilgel Abay, Gumara, Ribb, and Megech, respectively. In general, due to the rising atmospheric temperature, the amount of moisture during dry seasons in the headwater catchments of the upper Blue Nile basin is expected to deplete in the 21st century. Therefore, it is highly recommended to use different climate change adaptation mechanisms including adopting suitable physical and biological water conservation techniques to enhance the amount of water stored in the subsurface and joining the groundwater during the rainy season. [ABSTRACT FROM AUTHOR]

• Hydraulic Geometry parameters follow coherent spatial patterns in Brazil. • Basin area plays a strong control over the width and velocity parameters. • Cross-section width is mostly sensitive to discharge variation in arid basins. The geometry of river channels defines their discharge conveyance capacity and can alter the flood regime. While most rivers follow the Theory of Hydraulic Geometry at-a-station power laws, the spatial patterns of exponents, coefficients, and hydrological controls beyond the scale of river reaches remain unclear. Here, we analyze 290 Brazilian river cross-sections to test the hypothesis that the hydraulic geometry is related to basin hydroclimatic characteristics, with a significant difference between humid and dry basins. We classify the basins draining to each cross-section according to the aridity index and the baseflow index, and analyze the controls on the exponents and coefficients (i.e., parameters) of the at-a-station hydraulic geometry power-laws. Our results show that the exponents and coefficients follow a spatially coherent pattern. The exponent of the width of AGH power law is related to the aridity of the basin, being larger in drier basins with a low baseflow index. The width and velocity coefficients are strongly dependent on the basin area. Whereas the velocity coefficient decreases in large basins, the width coefficient increases in large basins, and the spatial distribution of width exponent is related to the bankfull cross-section shape. The combined analysis of hydraulic geometry and basin characteristics is a promising tool for discharge estimation in ungauged basins, flood management, and maintenance of natural rivers. [ABSTRACT FROM AUTHOR]

• We simulated carbon and water fluxes of alpine shrubs using the Biome-BGC model. • Optimized parameters based on PEST can be used to simulate alpine shrubs. • A biphasic relationship exists between water use efficiency (WUE) and aridity intensity. • The WUE of alpine shrubs with an aridity index of 0.34 is the highest. Water use efficiency (WUE), which is strongly related to carbon and water cycles, is crucial for maintaining fragile and sensitive alpine ecosystems. An accurate assessment of the spatial and temporal variations in WUE among alpine shrubs under different aridity levels is essential for quantifying the carbon and water balance in alpine environments. We calibrated the Biome-BGC model using the parameter estimation (PEST) approach with one year of data from an eddy covariance tower and validated the model against three years of carbon–water flux and carbon storage data from 80 biomass sampling sites in Qinghai Province, China. We then simulated the carbon and water cycles of alpine shrubs in Qinghai Province from 1980 to 2019. Using meteorological data from the study area, we analyzed the spatiotemporal variations and factors influencing WUE in regions with different aridity levels. The results showed that after optimization using the PEST approach, the mean absolute error (MAE) and root mean square error (RMSE) of gross primary productivity (GPP) decreased by 0.58 and 1.05 g C m−2 d−1, respectively, and those of evapotranspiration (ET) decreased by 0.41 and 0.77 mm d−1, respectively. Spatial distribution analysis revealed that the annual mean GPP and ET generally decreased from southeast to northwest in the order of humid, subhumid, semi-arid, arid, and hyper-arid climate regions. In other regions, WUE exhibited a biphasic trend with the aridity index, decreasing under severe dryness but increasing as aridity increased. The primary controlling factor in humid and sub-humid regions is the mean annual temperature, whereas in arid and semi-arid regions it is the mean annual precipitation. These findings are critical for improving the prediction of carbon sequestration and water-holding capacity of alpine shrublands under drought conditions. [ABSTRACT FROM AUTHOR]

This study introduces the climate of Iran determined according to Köppen-Geiger, Feddema, and UNPEP climate classifications, computed with a high-resolution ground-based gridded dataset for the 1985–2017 period. Ten Köppen-Geiger climate types were found for Iran, from which climate types "Bwh," "Bsk," "Csa," "Bsh," and "Bwk" cumulatively account for more than 98% of the territory. Likewise, fourteen Feddema's climate types were determined for Iran when only a combination of moisture and thermal factors were used for the classification, but a set of 24 climate types were identified when annual and seasonal characteristics were also incorporated in an exhaustive Feddema's climate classification. From these 24 climate types, "dry cool with extreme seasonal temperature," "semiarid hot with extreme seasonal temperature," "semiarid warm with extreme seasonal temperature," "semiarid torrid with extreme seasonal temperature," and "dry warm with extreme seasonal temperature" cover 24.55%, 15.32%, 14.92%, 14.40%, and 8.90% of Iran, respectively. These main climate types collectively cover more than 87% of Iran. Similarly, UNEP's climate types "arid," "semi-arid," "humid," and "sub-humid" characterized more than 98% of Iran. A few other vertically stratified climate types appeared over the highlands of Iran as a result of changes in elevation and slope aspects of the mountains. The spatial distribution of the climate types in all created climate classification maps reflects the general pattern of the topographical features of Iran, including the Alborz and Zagros mountain ranges. The combined effect of topography and vicinity to the Caspian Sea also creates very distinct climate types in northern Iran. The climate maps of the three used methods reflect the joint effects of topography, latitudinal variation, and land/sea surface contrast on the climate of Iran, which are jointly responsible for creating the diverse climate types of the country. A pairwise comparison made between the three classifications showed a satisfactory agreement between the three schemes in representing the main climate types of Iran. [ABSTRACT FROM AUTHOR]

• Rare examples of highly instrumented observatories in African drylands. • Large water surplus during monsoon not represented by annual scale of aridity index. • Overland flow is rare and root zone achieves field capacity across hillslopes. • Stable isotopes indicate recharge season timing, not a link to heavy rainfall. • Recharge is diffuse in semi-arid Africa validating soil moisture balance model use. We use two comprehensively instrumented field observatories to understand groundwater recharge processes in African drylands. The observatories are located on crystalline basement geology in semi-arid parts of Ghana and Burkina Faso, aridity indices 0.43 and 0.29, respectively, and we report 2017–2019 observations. Groundwater recharge was quantified by inverse water table fluctuation models using specific yield estimates derived from magnetic resonance soundings. Evidence for recharge drivers and mechanisms comes from high resolution meteorological observations, soil moisture (logged hourly and weekly along hillslope transects), overland flow plots, river stage, and stable isotopes of O and H in rainfall events and groundwater. Groundwater recharge varied between 87 and 175 mm/y, i.e. 7–15 % of annual rainfall. Rainfall was twice the volume of water lost via actual evapotranspiration across the four peak months (Jun-Sep) of the monsoon. This seasonal water surplus of ∼ 350 mm/y is not characterised by the annual scale of the aridity index. Overland flow was rare and soil moisture deficits were overcome at all monitoring locations. Large rainfall events only produced appreciable recharge when the antecedent soil moisture was close to field capacity, yet always produced large responses in river stage. Stable isotopes of O and H in groundwater indicate no evidence of evapotranspiration prior to infiltration and their composition is akin to depleted isotopic rainfall at the monsoon peak. Stable isotopes indicate recharge season timing and not a relationship between intense rainfall and groundwater recharge. We contend that the mechanism for groundwater recharge is predominantly diffuse in these semi-arid African settings. [ABSTRACT FROM AUTHOR]

In order to deeply understand the effect mechanism of rapid drought stress on the physiological and biochemical properties of crop leaves and determine drought thresholds, the potted spring wheat under two water treatments, adequate water supply and continuous drought stress, was researched. In the early stage of drought, the parameters of leaves decreased in the order of stomatal conductance (gs), intercellular CO2 concentration (Ci), maximum electron transfer rate (Jmax), mesophyll conductance (gm), photosynthetic rate (Pn,) leaf water content (LWC), triose phosphate utilization rate (TPU), transpiration rate (Tr), and maximum carboxylation rate (Vcmax). Photosynthesis was dominated by stomatal limitation and also limited by carboxylation and mesophyll limitation. The carboxylation limitation was mainly caused by the reduction of electron transport capacity. In the late stage of drought, stomatal limitation first decreased, and then mesophyll limitation decreased. During extreme drought, carboxylation limitation also decreased. With the decrease of relative soil moisture (RSM), except for Ci, which first decreased and then increased, other physicochemical parameters of leaves all showed an S-shaped, decreasing trend. Mild and severe drought thresholds were determined to be 56.6% and 43.6% of the RSM, respectively, according to the curve's inflection point, corresponding to 16.6% and about 52.2% of the average initial decrease amplitude among all parameters. This will provide a reference for monitoring as well as an early warning of rapid drought in spring wheat. [ABSTRACT FROM AUTHOR]

This study evaluates the potential of gridded AgMERRA (the Modern-Era Retrospective Analysis for Research and Applications) to estimate aridity index (AI), growing degree days (GDD), and temperature seasonality (TS) for six land stations across northeast Iran. The researcher investigated the spatiotemporal variation of the AgMERRA-derived agro-climatic indices for the entire period 1981–2010 and three 10-year sub-periods for the 347 wheat harvested grid cells (0.25° × 0.25°) and their utility for agro-climate zoning in northeast Iran. Results indicated a good agreement between AgMERRA daily solar radiation, maximum and minimum temperatures, and annual total precipitation with corresponding land observations for the six studied sites. AgMERRA-derived evapotranspiration (ETo), AI, GDD, and TS also exhibited good agreement (R2 and d > 0.7) with the land station–derived indices for most of the locations. Annual analysis of the AI indicated a negative trend for all of the wheat harvested grid cells, but the decrease was significant (p < 0.05) only for 14.70% of grid cells, which were located in the southwest part of the studied region. The magnitude of the significant decreasing trends in annual AI was (−)0.0011 per year. The increase in aridity was due to the concurrent occurrences of positive ETo trends and negative precipitation trends. All of the wheat harvested grid cells showed a significant increasing trend (p < 0.05) for GDD at the rate of 24.10 °C d year−1. The TS series demonstrated an apparent increasing trend for 99.2% of wheat harvested grid cells; however, only 16.9% of them had the significant positive trend (p < 0.05) with the average rate of 0.023 °C year−1. The wheat harvested grid cells with increasing trend for TS were mainly distributed in the arid mountainous southern part of the study area. The 10 years sub-periods revealed that the best conditions in terms of most of the studied agro-climatic indices were found in sub-period 1981–1990 and the north Khorasan had better conditions in all three sub-periods. Based on AI, GDD, and TS, 13 major gridded agro-climatic zones were recognized in northeast Iran. [ABSTRACT FROM AUTHOR]

Aim: Biodiversity drives the delivery of multiple ecosystem functions related to carbon and nutrient cycling (ecosystem multifunctionality, EMF), and biodiversity and ecosystem functioning are strongly threatened by intensive grazing in grasslands. However, it remains unclear how biodiversity regulates EMF changes in response to intensive grazing. Location: Global. Time period: From 1992 to 2018. Major taxa studied: Grassland. Methods: Here, we conducted a global synthesis using 373 paired observations from 90 published studies to address the responses of plant diversity, EMF and their relationships to grazing disturbance depending on grazing intensity, livestock type, grazing duration, and climatic aridity. Results: Our results showed that EMF significantly decreased with increasing grazing intensity, but the negative EMF response was alleviated at high levels of plant diversity. The grazing‐induced changes in EMF increased linearly with the changes in plant diversity, with the slopes increasing by 78.9% from light to heavy grazing. In addition, the grazing‐induced decrease of EMF was stronger with longer grazing duration and more arid climates. Structural equation models suggested that grazing intensity reduced EMF largely via decreasing plant diversity, whereas upsizing livestock type promoted EMF by increasing plant diversity. Main conclusions: This study highlights the key role of biodiversity in mediating EMF in response to intensifying grazing disturbance. We call for conservation of biodiversity to maintain grassland multifunctionality and services. [ABSTRACT FROM AUTHOR]

Crop yield in rainfed conditions is greatly influenced by meteorological parameters such as rainfall and evapotranspiration. As climate indices (AO, NAO, PNA, NINO-3.4, and AAO) are available for the future months, finding the relationship between crop yield with meteorological parameters and the relationship between meteorological parameters with climate indices can be very useful in predicting annual fluctuations in rainfed crop yield. In the current study, the association between rainfall, PET, and AI with barley and wheat rainfed detrended yields (1990–2016) and the relationship between AI and climate indices (AO, NAO, PNA, NINO-3.4, and AAO) were assessed for Chaharmahal and Bakhtiari province in the west of Iran. All associations were assessed at annual and seasonal (wet and dry seasons) scale considering both concurrent and lag correlations (1-year and 2-year lag). Our results showed a significant correlation between rainfall and AI with crop yields in all study locations except Kouhrang in both annual and wet season time scales. The results indicated that except Kouhrang, where the temperature is a limiting factor to crop yields, in all Chaharmahal and Bakhtiari areas, drought is one of the key factors of annual yield variability (significant correlation between AI and crop yields). The significant correlation between AI with NINO-3.4 and AAO also was observed in both annual and wet season time scales. It seems that NINO-3.4 and AAO indices can be useful to estimate grain yield of rainfed barley and wheat, predict drought occurrence, and take possible actions to counter such conditions. [ABSTRACT FROM AUTHOR]

The temperature and moisture distribution over the Indian subcontinent are changing in recent decades with the accelerated global temperature rise. These changes in distribution result in shifting wet/dry and warm/cold zones within India. The differential warming rate over land and surrounding ocean determine intricate dynamics of the Indian summer monsoon (ISM) and make the Indian region a more susceptible towards drought and flood events. In recent time, the frequent flooding over northwest India viz., over Gujrat and southern Rajasthan is attributed to the weakening of prevailing heat-trough circulation (northerly wind) and gradual increase in the convective activity (enhanced moist static energy). The recent weakening of the southwesterly reduced transport of moisture leading to reduced rainfall over Indo-Gangetic Plain (IGP) and northeast India; while the strengthening of the same enhanced the moisture transport and hence the rainfall over northwest India. In addition, northward shift of the sinking airmass over equatorial region, in recent time, leads to the decrease of the rainfall over the southern Indian region. The recent changes in rainfall pattern have shifted the climate of IGP and northeast India towards the relatively arid regime and that of western India towards a relatively moist regime, which supports the possible greening of the Thar region. The recent change in rainfall distribution in the form of wet and dry zones across the country will impact the water resource, food security as well as the fragile local ecosystems. [ABSTRACT FROM AUTHOR]

One of the most celebrated textbook examples of physiological adaptations to desert environments is the unique ability that desert mammals have to produce hyperosmotic urine. Commonly perceived as an adaptation mainly observed in small rodents, the extent to which urine‐concentrating ability has evolved independently in distinct mammalian lineages has not previously been assessed using modern phylogenetic approaches.We review urine‐concentrating ability data from the literature in 121 mammalian species with geographic ranges encompassing varying climatic conditions. We explicitly test the general hypothesis that desert‐dwelling mammals have evolved greater ability to concentrate urine than non‐desert species, controlling for body mass, phylogenetic affinity and other covariates.Ancestral state reconstruction across our dataset's phylogeny shows that the ability to produce hyperosmotic urine, measured as maximum urine osmolality, has evolved convergently in mammalian species with geographic ranges characterised by low mean annual aridity index.Phylogenetic generalised least‐squares (PGLS) models show that the mean annual aridity index of a species' geographic range largely predicts its urine‐concentrating ability, even when accounting for body mass differences, phylogenetic correlations, the specific condition under which urine osmolality was measured, the method used to measure urine osmolality, and the species' diet.In contrast, we find much weaker correlations between mass‐adjusted basal metabolic rate and environmental variables when analysing 84 of the species included in the urine osmolality analysis.Taken together, our results not only show that desert mammals effectively concentrate more urine than non‐desert mammals, but further suggest that aridity is likely to have been one of the main selective pressures leading to increasing maximum urine‐concentrating ability and driving its repeated evolution in different desert mammalian lineages. [ABSTRACT FROM AUTHOR]

Global warming is already having a negative impact on vital sectors on which human development depends, such as water resource availability. In this study, the changes and abrupt change timing of climatic extreme indices, aridity and drought over the Region of South Aegean are captured using the Mann–Kendall and Pettitt tests, while the latter variables are correlated with the water volume transported by ships to the region as well as the relevant costs. The region's climate is shifting to warmer conditions with less precipitation, since significantly positive trends were noted with regard to the number of tropical nights, warm nights, warm days, the warm spell duration index and the diurnal temperature range; significant negative trends were observed in relation to the number of cool nights, cool days and the cold spell duration index, with the change-point year for the latter variables being 2006. Inaddition, 7/11 precipitation related indices exhibited a downward trend, while significantly negative trends were observed with regard to the number of consecutive dry days, with the timing of the abrupt change being 2001. The Aridity Index (AI) reveals that the region's climate characterization is changing from dry and sub-humid to semi-arid conditions, whilst the Reconnaissance Drought Index standardized (RDIst) and the Standardized Precipitation Index (SPI) indices suggests an amplification of drought phenomena over the Region. The tourism variables illustrated a significant positive trend, with the timing of the abrupt change being registered during 2006–2009, whilst the correlation analysis between tourism variables and water transfers implies that the surge on water transfer by ships to the Region occurred between 1998 and 2008. This can be mainly attributed to the changes in climate patterns. The correlation analysis documents a strong positive correlation between the water transfer dataset and the diurnal temperature range, and a moderately negative association with the precipitation related indices, annual precipitation, drought phenomena and aridity with 7/11. [ABSTRACT FROM AUTHOR]

Unlike other crops, beans have moderate moisture requirements, but are very sensitive to moisture deficiency during flowering and grain formation. It has been established that in the short interval between these phenophases the sensitivity is maximum both in case of excess moisture and moisture deficit. Research has shown that the lack of water during flowering and fruiting greatly reduces production by shortening the duration of these phases of vegetation, by reducing pollen fertility, reducing pods and grain weight. The sensitivity of beans to the deficiency of vapor saturation in the atmosphere during flowering also has negative effects on the harvest. In order to determine to what extent the years of experimentation approach or deviate from the climatic conditions typical of the experimental field, monthly aridity indices were used for the series of years in which the experiments were performed at the studied farms, compared to indices of aridity from a longer period. The highest yields were obtained when the soil moisture at the beginning of flowering was at the field capacity for water and was maintained at the mentioned ceilings until the full formation of the grains. This paper summarizes the results of research on the influence of irrigation on production obtained in 2018-2021, at four farms located in the North Baragan Plain in Braila County. [ABSTRACT FROM AUTHOR]

Climate zones fundamentally shape the patterns of the terrestrial environment and human habitation. How global warming alters their current distribution is an important question that has yet to be properly addressed. Using root-layer soil moisture as an indicator, this study investigates potential future changes in climate zones with the perturbed parameter ensemble of climate projections by the HadGEM3-GC3.05 model under the CMIP5 RCP8.5 scenario. The total area of global drylands (including arid, semiarid, and subhumid zones) can potentially expand by 10.5% (ensemble range is 0.6–19.0%) relative to the historical period of 1976–2005 by the end of the 21st century. This global rate of dryland expansion is smaller than the estimate using the ratio between annual precipitation total and potential evapotranspiration (19.2%, with an ensemble range of 6.7–33.1%). However, regional expansion rates over the mid-high latitudes can be much greater using soil moisture than using atmospheric indicators alone. This result is mainly because of frozen soil thawing and accelerated evapotranspiration with Arctic greening and polar warming, which can be detected in soil moisture but not from atmosphere-only indices. The areal expansion consists of 7.7% (–8.3 to 23.6%) semiarid zone growth and 9.5% (3.1–20.0%) subhumid growth at the expense of the 2.3% (–10.4 to 7.4%) and 12.6% (–29.5 to 2.0%) contraction of arid and humid zones. Climate risks appear in the peripheries of subtype zones across drylands. Potential alteration of the traditional humid zone, such as those in the mid-high latitudes and the Amazon region, highlights the accompanying vulnerability for local ecosystems. [ABSTRACT FROM AUTHOR]

The transitional climate zone (TCZ) over East Asia is an interface area between monsoon circulation and westerly circulation, making it highly susceptible to natural disasters and climate change. This study explores the spatial–temporal variation of the summer (May–September) TCZ during 1961–2018 and its response to monsoon rainy season. The summer Aridity Index (AI) instead of annual amount is used to recognize summer TCZ, with similar domain produced. However, differing from the annual total, the summer evaporation remains stable during the whole period, despite global warming. Hence, the summer TCZ has experienced little significant long‐term trends toward wetter or drier, since it is predominantly driven by precipitation that shows no clear tendency. The EOF decomposition reveals three key patterns accounting for 58.2% of the total variance: spatially uniform, south–north dipole and meridional tripole, which shows the complexity of spatial‐temporal variation in TCZ. TCZ is characterized by interdecadal mutations and periodical oscillations of 3 or 8 years. There exist remarkable 3 years interannual periods, with the greatest contribution stemming from the south‐central part of TCZ. In comparison, the northeast part exhibits a significant interdecadal band of about 8 years, which promotes the regime shift from wet to dry in the late 1990s over TCZ. Furthermore, the onset, retreat, and duration of the rainy season of TCZ in response to summer monsoon are examined, based on EEMD filtered 4 mm/day precipitation. All three indicators are subjected to strong interannual dispersion, without any significant overall trends. Only the retreat date of the western part of TCZ (100–110°E) is significantly correlated with the onset date. Dry‐wet condition in TCZ is more closely associated with the duration length of the monsoon influence. And we also notice that the westmost part of TCZ shows a greater sensitivity to monsoon activity than the east part. [ABSTRACT FROM AUTHOR]

Desertification is a serious threat to human development and sustainability. This process is characterized by land degradation over areas with dry sub‐humid, semi‐arid and arid climate. In this work, climate susceptibility to desertification was identified for the state of Rio de Janeiro (SRJ), Brazil, the third most populated state in the country. The state is characterized by complex topography, and diverse climate and land uses. Two formulations for the aridity index were used: Ia, defined by Thornthwaite (1948, Geographical Review, 38(1), 55–94) and Penman (1953, Horticultural Congress, 2, 913–924), and D, a modification of Ia by Hare (1983, Climate and Desertification: A Revised Analysis, Geneva: World Meteorological Organization). Both estimates of the aridity require annual rainfall and potential evapotranspiration, which were calculated from the climatological water balance using times series of rainfall and air temperature (1961–2010) from 98 stations over the SRJ. Annual rainfall, evapotranspiration, water deficit and the aridity indices were then spatially interpolated over a 5 × 5‐km grid using a spline tension method. Both indices agree on the driest regions of the SRJ: Norte and Baixada Litorânea, near the northern coast, both under sub‐humid and semi‐arid climate. The index Ia indicated susceptibility to desertification over 2,305 km2 on the Norte and Baixada Litorânea regions, which correspond to 5% of SRJ area; similarly, the index D classified a smaller area over the Norte region under desertification (431 km2). These subregions, among the others also considered in this study, are of great importance for the agricultural, forestry and tourism industries and contribute immensely to the economic development of the state. Hence, the evaluation of susceptibility to desertification in those areas is essential to help prevent further land degradation and support policies formulation on long‐term sustainable management of land and water resources, especially under regional and global climate change scenarios. The methodology used in this work can be applied to studies of desertification in other regions of the world. [ABSTRACT FROM AUTHOR]

In this study, we project the global terrestrial changes in Aridity Index (AI), as defined by the ratio of annual precipitation to potential evapotranspiration (PET), at 2 and 4°C levels of global warming above the preindustrial conditions based on the outputs from 21 Coupled Model Intercomparison Project Phase 5 models under the Representative Concentration Pathways 8.5 (RCP8.5) scenario. Compared to the preindustrial period, the global terrestrial annual precipitation will increase by an average of 0.02% (3%), the annual PET will increase by 6% (15%) and AI will decrease by 0.1 (0.2) at the 2°C (4°C) warming level. More remarkable decreases in the annual AI are seen in the northern high latitudes, where will also experience greater increases in PET and precipitation. In general, the seasonal changes in AI display a similar spatial pattern to the annual changes and are characterized by the greatest decrease in December–January–February and the smallest in June–July–August. The largest expansion of drylands occurs in semi‐arid regions, followed by the expansion of arid regions, with area changes of 4% (7%) and 3% (4%) under the 2°C (4°C) scenario, respectively. Further analyses indicate that the AI changes are determined by PET in the northern high latitudes, and the contribution of PET to AI increases from the 2 to 4°C warming levels. Furthermore, changes in thermodynamic factors contribute most to the PET, and at a higher level of global warming, the contribution of thermodynamic factors increases and that of dynamic factors decreases. [ABSTRACT FROM AUTHOR]

Water flow in the Polish Carpathians was exemplified by long-term (1988-2017) analysis of two foothill catchments (of the Skawinka and Stobnica) and two catchments in the Beskidy Mountains (of the Soła and Osława). The work allowed for the determination of the duration of low flows and outflow deficits in relation to changes in thermal and precipitation conditions, as well as land use and land cover. In the selected catchments, the 30-year period brought a decrease in the area of arable land and an increase in the area of grassland and forest. In addition built-up areas increased by 495% between 1990 and 2018. A greater susceptibility to the occurrence of total drought was noted for the Beskidy Mountains catchments, in which the duration of low flows and outflow deficit was greater than in the foothill catchments. At the same time, the mountain catchments proved less susceptible to the emergence of deep drought, on account of their higher levels of forest cover and levels of soil permeability. In regional terms, the durations of low flows and outflow deficits were greater in the catchments located in the eastern part of the Carpathians (those of the Stobnica and Osława), in line with this area's intensified features of a continental climate. [ABSTRACT FROM AUTHOR]

Information about the past evolutionary changes in the soil cover is essential as a retrospective basis for long-term forecasts of soil development under the changing climatic conditions, and also for understanding the present-day problems of desertification and land degradation in the south of the East European Plain. The principal task of the present study was to estimate quantitatively the shift of the boundary between the steppe and desert-steppe zones in this region during the late Holocene under the impact of global climate variations. The properties of about 100 paleosols of archaeological sites widely represented in the region were used for quantitative reconstruction of paleoprecipitation, paleotemperature, and climate aridity. To obtain regional calibrations, the dependences of the magnetic properties of modern soils on climatic parameters in the south of the East European Plain were analyzed in detail. Samples of 35 soil profiles along the 1500-km-long Voronezh–Volgograd–Astrakhan–Elista–Voronezh transect were used. This transect crosses several natural climatic zones with gradients in the annual precipitation of about 500 mm/yr and in the annual temperatures of about 3°C, which allowed us to obtain reliable relationships between the climatic parameters and the properties of recent soils. Limitations for paleoclimate reconstructions based on the magnetic properties of soils in the range of mean annual precipitation <600 mm/year were identified. Cartographic reconstruction of changes in the De Martonne aridity index (IDM) using GIS modeling methods and paleopedological data indicates that the Volga–Don interfluve has undergone repeated changes in the climatic situation over the past 5000 years resulting in the shifts of the boundaries between soil-geographical zones to distances of up to 200–300 km. [ABSTRACT FROM AUTHOR]

Previous studies that observed the fact that Middle Palaeolithic sites mainly were concentrated in arid and semi-arid areas in Africa and Southwest Asia, concluded that climate factors determined the distribution patterns. We argue that biological factors could have been equally important. In present-day sub-Saharan Africa, mosquito-borne diseases and especially falciparum malaria have a serious impact on human populations. This study was aimed to investigate the possible former effect of falciparum malaria on Middle Palaeolithic site distribution patterns and explain why ancient humans avoided the humid areas in the tropical and subtropical regions. It was found that the early human settlements situated in those regions of Africa and Southwest Asia where the potential annual development period of falciparum parasites was short in the mosquitoes, the area was not too humid, and the potential falciparum malaria incidence values were low or moderate. In the Indian Peninsula, precipitation played a less significant role in determining human settlements. The number of the months when the extrinsic development of Plasmodium falciparum parasites was possible showed the strongest structural overlap with the modelled malaria incidences according to the spatial occurrence of the Middle Paleolithic archaeological sites in the case of Africa and in Southwest Asia. In the Indian Peninsula, climatic factors showed the strongest structural overlap with the modelled malaria incidences according to the occurrence patterns of the Middle Palaeolithic archaeological sites. Image 1 [ABSTRACT FROM AUTHOR]

The 100th meridian is a conceptual arid‐humid divide that effectively bisects the continent of the United States into the humid east and arid west. Here, we examine the historical and future shifts of the 100th meridian from atmospheric, hydrologic, and agroecological perspectives. We find that the effective arid‐humid divide regarding vegetation greenness and runoff has been moving toward west with a mean shift of 0.73° (1982–2015) and 2.08° (1961–2010), respectively, suggesting decreased agroecological and hydrologic aridity in the region. For future periods, the agroecological divide shows a persistent westward movement, whereas eastward shifts of the 100th meridian are detected from the atmospheric and hydrologic perspectives. Nevertheless, the eastward movements of the atmospheric and hydrologic divide substantially slow down when the vegetation response to elevated atmospheric CO2 is accounted for. This finding demonstrates that CO2 fertilization on vegetation could largely alleviate the warming‐induced drying tendency around the 100th meridian region. Plain Language Summary: The 100th meridian is a conceptual arid‐humid divide in the physical climate and landscape of the central United States continent and has exerted a profound influence on human settlement and agriculture developments. Using climate projections and aridity index, a previous study reported an eastward movement of the 100th meridian, indicating an overall drying trend in the region. Here, we reexamine the historical and future shifts of the 100th meridian from the atmospheric, hydrologic, and agroecological perspectives. We find that the movements of the 100th meridian are strongly modified by the vegetation response to elevated atmospheric CO2 concentration that CO2 fertilization on vegetation could largely alleviate the warming‐induced drying tendency and effectively slows down the eastward movement of the arid‐humid divide. Key Points: Historical and future shifts of the 100th meridian from atmospheric, hydrologic, and agroecological perspectives are assessedObserved hydrologic and agroecological 100th meridian have been moving toward west over the past few decadesProjected agroecological divide moves toward west whereas hydrologic and atmospheric divides move toward east in the coming century [ABSTRACT FROM AUTHOR]

Intense anthropogenic climate changes are expected to increase atmospheric aridity in the 21st century. The aridity index (AI), defined as the ratio of annual precipitation (Pre) to atmospheric evaporation (potential evapotranspiration [PET]), represents an efficient indicator of climatic changes. However, the variations and underlying drivers of AI values have not been comprehensively compared in different climatic regions. Using the AI calculated on the basis of bias‐corrected precipitation and optimized PET over the period of 1999–2017 and two climate model projections for the coming century, we investigated the response of the AI to climate change and quantified the contributions of climatic factors to AI variations in eight climatic regions in China, that is, the northwest (NW), north‐centre (NC), northeast (NE), North China Plain (NCP), east (E), southeast (SE), southwest (SW) and Tibet Plateau (TP). The results indicated that the AI values in seven of the eight climate regions exhibited negative trends from 1999 to 2017, with mean values ranging from −0.0008 in SW to −0.0414 in NC, while the AI values in the TP region showed a significant positive trend, with a value of 0.0124. Pre was the dominant factor for the variations in AI values in all climate regions, with contribution rates from 65 to 308%, followed by decreasing solar radiation in the NW, NC, E, SE and SW regions; deceasing wind speed in NE and NCP; and deceasing actual vapour pressure in the TP. The effect of increasing temperature on the AI trend was offset by other climate factors. By the end of the 21st century, under the Representative Concentration Pathway 8.5 emission scenario, the AI will significantly increase in five of the eight regions to values approximately 16.5% higher than those during 1999–2017, and this increase in the AI will be dominated by increasing PET. Overall, the shift in the dominant AI factor from Pre in recent years to PET in the future indicates that more attention should be given to the response of the AI to global warming. Furthermore, regional differences in climate change and AI values during 2018–2,100 will inevitably influence water availability and urgently require the development of adaptation strategies for different climatic regions. [ABSTRACT FROM AUTHOR]

Abstract The objective of this paper is to study the spatial and temporal variation characteristics of the UNESCO aridity index (AI) at annual and seasonal temporal scales in northwestern China during the 55-year study period (1961–2015). Based on climate data from 178 meteorological stations provided by the China Meteorological Data Service Center, AI trends were investigated by the Mann-Kendall test. The results showed that the annual and seasonal AIs displayed a mixed pattern of positive and negative trends for the period of 1961–2015 across the study area. In most regions, both annual and seasonal AIs exhibited slightly positive trends in northwestern China. Significant (P <.05) positive and negative annual trends were detected at 38 and 6 stations, respectively. The highest magnitude of the positive annual trend (0.0037 per year) appeared at Xining station, and the greatest decreasing annual trend (−0.0041 per year) appeared at Minxian station. In terms of seasonal AI, its trend magnitudes varied from −0.0058 to 0.0035 in spring, from −0.0062 to 0.0087 in summer, from −0.0105 to 0.0048 in autumn and from −0.0002 to 0.0443 in winter each year. Our study demonstrated that the AI spatial distribution may tend to be spatially homogeneous in the long term. Abrupt changes varied in different regions and seasons. Nevertheless, the positive trend shifts mostly began in the 1980s and became significant in the following decades. The correlation analysis indicated that the AI in winter and spring was probably mainly affected by the Indian Ocean Warm Pool Strength Index (IOWPSI), while the Multivariate ENSO Index (MEI), the Niño3.4 Sea Surface Temperature Anomaly Index (Niño3.4 SSTA) and the Southern Oscillation Index (SOI) were likely to be the conjoined influencing factors of the AI in summer and autumn. The spatiotemporal features of the long-term AI provided in this study may enhance our scientific understanding of the impacts of recent climate change on dryness/humidity changes in northwestern China; furthermore, this information might potentially be applied in other areas for comparison purposes. Highlights • Most of the significant trends were positive, whose shifts mostly began in the 1980s. • The arid areas were becoming more humid and vice versa. • The IOWPSI was the most dominant factor in winter and spring. [ABSTRACT FROM AUTHOR]

Assessing trends of hydrologic variables related to both hydrologic processes facilitates accurate water resources forecasting, especially in arid and semiarid regions with high evaporation and low rainfall volume. In this study, spatial and temporal trends of six hydrologic and climatic variables, viz. rainfall, evaporation, streamflow discharge, temperature, wind speed and relative humidity and also the ratio of annual potential evaporation to precipitation (E/P) were analysed at a monthly and annual scale. Moreover, the relationship of relative humidity, temperature, rainfall and wind speed trends with evaporation trend was investigated. Results of the study revealed the absence of significant temporal trend in precipitation, temperature and wind velocity for the majority of months, and the presence of upward trends in relative humidity and evaporation values as well as downward trend in streamflow discharge in some months. At an annual scale increasing evaporation and decreasing stream flow discharge trends were observed at most stations, which means that the region will be confronted with more severe drought conditions in future. Also, the result of Spearman's rank coefficient revealed that the temporal evaporation trend is not related to wind speed, temperature, relative humidity and rainfall trend. Moreover, the spatial trend of climatic and hydrologic variables indicated the similarity of evaporation and relative humidity trend as well as wind speed and rainfall trend. [ABSTRACT FROM AUTHOR]

Assessing trends of hydrologic variables related to both hydrologic processes facilitates accurate water resources forecasting, especially in arid and semiarid regions with high evaporation and low rainfall volume. In this study, spatial and temporal trends of six hydrologic and climatic variables, viz. rainfall, evaporation, streamflow discharge, temperature, wind speed and relative humidity and also the ratio of annual potential evaporation to precipitation (E/P) were analysed at a monthly and annual scale. Moreover, the relationship of relative humidity, temperature, rainfall and wind speed trends with evaporation trend was investigated. Results of the study revealed the absence of significant temporal trend in precipitation, temperature and wind velocity for the majority of months, and the presence of upward trends in relative humidity and evaporation values as well as downward trend in streamflow discharge in some months. At an annual scale increasing evaporation and decreasing stream flow discharge trends were observed at most stations, which means that the region will be confronted with more severe drought conditions in future. Also, the result of Spearman's rank coefficient revealed that the temporal evaporation trend is not related to wind speed, temperature, relative humidity and rainfall trend. Moreover, the spatial trend of climatic and hydrologic variables indicated the similarity of evaporation and relative humidity trend as well as wind speed and rainfall trend. [ABSTRACT FROM AUTHOR]

Abstract Understanding response of streamflow to environmental changes is crucial for large-scale water resources management and ecosystem restoration. There is no consensus on how environmental change influence streamflow in different regions across climate gradient, as previous studies mainly focused on a single river basin or climate region. This study analyzed the variations of aridity index and its contributions to streamflow change based on Budyko's framework approach using bias-corrected precipitation measurement, parameters-optimized potential evapotranspiration and observed streamflow in 144 basins across China. The parameter n in the Budyko type equation exhibits significant spatial heterogeneity, with larger values in the water-limited region than in the energy-limited region, which suggests more pronounced impact of basin characteristic or vegetation change on hydrological cycle. The absolute value of sensitivity coefficient in the water-limited region (−2.56) was larger than both equitant (−2.13) and energy limited region (−1.57), indicating that the streamflow was more sensitive to aridity index change in the water-limited region than in the equitant and energy-limited regions. The dominant factor affecting streamflow under energy-limited and equitant conditions is aridity index (i.e. climate change), with median relative contribution rates of 79.9% and 55.5%, respectively. In contrast, non-climatic factors dominate the variation of streamflow in the water-limited region, the effect of climate change on streamflow has been offset by other factors. This study suggests that the water management practices, such as water diversion across river basins and ecological restorations, should fully consider the differences in hydrological responses to climatic conditions. Graphical abstract Unlabelled Image Highlights • Bias correction to precipitation and optimization to a s and b s are essential for aridity index application • Streamflow is more sensitive to climate change in water-limited region than that in equitant and energy-limited region • Streamflow is dominated by climate in energy-limited and equitant regions and by other factors in water-limited region [ABSTRACT FROM AUTHOR]

Aims: Plant pH is a functional trait deserving more attention than the current few studies at local scales, given its roles in nutrient cycling and physiological processes. How plant pH varies and is regulated at large scales remain unclear. Here we explore the biogeography of foliar pH and the potential drivers. Location: East–west transect of northern China with increasing aridity westward. Time period: 2016–2017. Major taxa: Spermatophytes. Methods: We analysed foliar pH of plants from 22 sites across northern China, and investigated its spatial pattern and relationships with climate, soil, and plant functional type (PFT). Results: Foliar pH was generally acidic (5.33 ± .04) in northern China, showing distinct geographical variability: foliar pH decreased significantly westward at an average rate of 0.25 units per 10° longitude. Climate, soil and PFT explained 11, 17 and 59% of the variance in foliar pH, respectively. Foliar pH decreased (about 0.16) with mean annual precipitation (per 100 mm), soil stress coefficient (per 10%) and aridity index (per 0.14), but increased with mean annual temperature (per 2 °C). Across PFTs, herbs exhibited higher foliar pH than woody plants (6.0 vs. 4.9); gymnosperms relative to angiosperms had lower foliar pH (3.7 vs. 5.6); and monocotyledons showed higher foliar pH compared with dicotyledons (6.0 vs. 5.5). Main conclusions: This study provides the first comprehensive analysis of the evident pattern of foliar pH over a large spatial scale. Foliar pH is higher in warm‐arid northwestern relative to cold‐humid northeastern China and in later‐ than earlier‐evolved plants. Similar to leaf mineral elements, foliar‐pH biogeography is shaped by the joint effects of climate, soil and PFT; PFT and moisture are the most influential factors. Our findings provide a new impetus for understanding functional biogeography, and lay the groundwork for research on the linkage of foliar pH to ecological functions and macroevolutionary implications. [ABSTRACT FROM AUTHOR]