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Numerous recent studies have argued that moisture limitation is leading to growth declines and mortality of black spruce (Picea mariana) and white spruce (Picea glauca) in the North American boreal forest. A parallel line of research suggests that increasingly common severe wildfires are altering successional pathways and leading to long‐term replacement of spruce forests with those dominated by paper birch (Betula papyrifera, Betula neoalaskana) and trembling aspen (Populus tremuloides). When both conifers and deciduous trees establish after fire, this biome shift hypothesis implicitly assumes that deciduous species will outcompete the conifers, owing to their more rapid vertical growth and because they might be less sensitive to warm and dry conditions.We established a research site in a white spruce‐paper birch forest on an east‐facing slope in interior Alaska and tested the hypothesis that Alaska paper birch are better adapted to warm and dry conditions than white spruce. Over 6 years (2013–2018), we made hourly measurements of microclimate and xylem sap flux of both species. We also collected increment cores and conducted climate‐growth analyses for both species.During our 6‐year study, growing seasons with low volumetric soil water content (SWC) were those that followed shallow winter snowpacks and had limited summer rainfall, not necessarily those with warm air temperature. Both species were sensitive to moisture limitation. The tree‐ring data revealed significant positive effects of cumulative water year precipitation on radial growth, with a steeper slope for paper birch than for white spruce. Radial growth of both species was also positively related to mean water year air temperature. Sap flux density declined progressively for white spruce over the range of observed SWC and abruptly for paper birch when SWC fell below ~15%.Synthesis. Our results show that, while paper birch might be less sensitive to mild drought than white spruce, it may be more sensitive to severe drought, raising questions about the ability of paper birch to outcompete co‐occurring white spruce in a drier climate. [ABSTRACT FROM AUTHOR]

Rhizobacteria play a crucial role in plant growth and yield, stimulating primary production and improving stress resistance. Climate change has several consequences worldwide that affect arable land and agriculture. Studies on plant–soil–microorganism interactions to enhance plant productivity and/or resistance to abiotic stress may open new perspectives. This strategy aims to make agricultural‐relevant plant species able to complete their biological cycle in extreme soils with the help of inoculated or primed plant growth‐promoting rhizobacteria (PGPR).We provide an overview of the evolution of interest in PGPR research in the last 30 years through: (i) a quantitative search on the Scopus database; (ii) keyword frequencies and clustering analysis, and (iii) a keyword network and time‐gradient analysis.The review of scientific literature on PGPR highlighted an increase in publications in the last 15 years, and a specific time gradient on subtopics, such as abiotic stresses. The rise in PGPR as a keyword co‐occurring with salinity and drought stresses aligns with the growing number of papers from countries directly or partly affected by climate change.The study of PGPR, its features, and related applications will be a key challenge in the next decades, considering climate change effects on agriculture. The increased interest in PGPR leads to deeper knowledge focused specifically on researching agriculturally sustainable solutions for soils affected by salinity and drought. [ABSTRACT FROM AUTHOR]

Highly fragile small island states experience disproportionate climate impacts given their limited capacity to implement cost‐effective tools for detecting emerging signals of drying conditions and monitoring systems for sensitive sectors such as agriculture, especially for uncertain, ‘creeping’ events such as droughts. Despite the existence of open‐source Google Earth Engine datasets, untapped potential remains for their full deployment in disaster management infrastructure. Given this gap, this paper explores the utility of the Enhanced Vegetation Index (EVI) for detecting spatio‐temporal variations of Mid‐Summer Drought (MSD) impacts on vegetation in the small island of Jamaica, with emphasis on major historical drought events. Geospatial analyses of EVI datasets from the Terra Moderate‐Resolution Imaging Spectroradiometer (MODIS) between 2000−2015 archived by the United States Geological Survey (USGS), were computed, and validated by station‐based precipitation and production data for selected parishes for historical case study MSD events. Results revealed highly asymmetrical drought impacts, with Jamaica's agriculturally intense Southern coastline displaying the most stressed vegetation (EVI < 0.5). North‐Western and North‐Eastern regions had the healthiest vegetation during the MSD (EVI > 0.6). A ‘fair’ to ‘moderate’ concurrent correlation was found between EVI and precipitation (R > 0.6), with lower correlations vis‐a‐vis agricultural production (R = 0.2–0.4). The results provide evidence of EVI's utility as a drought monitoring tool in a small island context. [ABSTRACT FROM AUTHOR]

Global hydrological reanalyses are modelled datasets providing information on river discharge evolution everywhere in the world. With multi‐decadal daily timeseries, they provide long‐term context to identify extreme hydrological events such as floods and droughts. By covering the majority of the world's land masses, they can fill the many gaps in river discharge in‐situ observational data, especially in the global South. These gaps impede knowledge of both hydrological status and future evolution and hamper the development of reliable early warning systems for hydrological‐related disaster reduction. River discharge is a natural integrator of the water cycle over land. Global hydrological reanalysis datasets offer an understanding of its spatio‐temporal variability and are therefore critical for addressing the water–energy–food–environment nexus. This paper describes how global hydrological reanalyses can fill the lack of ground measurements by using earth system or hydrological models to provide river discharge time series. Following an inventory of alternative sources of river discharge datasets, reviewing their advantages and limitations, the paper introduces the Copernicus Emergency Management Service (CEMS) Global Flood Awareness System (GloFAS) modelling chain and its reanalysis dataset as an example of a global hydrological reanalysis dataset. It then reviews examples of downstream applications for global hydrological reanalyses, including monitoring of land water resources and ocean dynamics, understanding large‐scale hydrological extreme fluctuations, early warning systems, earth system model diagnostics and the calibration and training of models, with examples from three Copernicus Services (Emergency Management, Marine and Climate Change). [ABSTRACT FROM AUTHOR]

Changes in precipitation patterns with climate change could have important impacts on human and natural systems. Zhang et al. (2021, https://doi.org/10.1029/2020gl092293) report trends in daily precipitation patterns over the last five decades in the western United States, focusing on meteorological drought. They report that dry intervals (calculated at the annual or seasonal level) have increased across much of the southwestern U.S., with statistical assessment suggesting the results are statistically robust. However, Zhang et al. (2021, https://doi.org/10.1029/2020gl092293) preprocess their annual (or seasonal) averages to compute 5‐year moving window averages before using established statistical techniques for trend analysis that assume independence about some fixed trend. Here we show that the moving window preprocessing violates that independence assumption and inflates the statistical significance of their trend estimates. This raises questions about the robustness of their results. We conclude by discussing the difficulty of adjusting for spatial structure when assessing time trends in a regional context. Plain Language Summary: A recent paper reports trends in drought in the western United States, in particular increases in drought in the southwestern United States, based on changes in the lengths of time intervals without precipitation. In this "comment" we note that the preprocessing approach used in the paper artificially increases the apparent statistical signal in the data and caution that the evidence for the trends reported is not as strong as presented in the paper. We conclude by discussing the difficulty of estimating trends in a statistically rigorous fashion across multiple weather stations. Key Points: Statistical uncertainty about trends in droughts in the southwestern US is larger than reported in a recent GRL letter [ABSTRACT FROM AUTHOR]

Paciorek and Wehner raise important questions around our use of the Mann‐Kendall nonparametric trend test on smoothed data for analyzing long‐term hydrometeorological trends in Zhang et al. (2021, https://doi.org/10.1029/2020gl092293). We thank them for initiating this important conversation and their gracious cooperation in exploring the issues addressed in their comment. In this reply we confirm the inflation of significant p‐values by our choice to smooth, illustrate the relatively minor impacts on the main conclusions of our paper, and add our voices to those of Paciorek and Wehner in highlighting the lack of methodology for hypothesis testing across multiple stations that have spatial structure (i.e., testing for regionally consistent trends). Plain Language Summary: Our colleagues Drs. Paciorek and Wehner have raised concerns about our paper (Zhang et al., 2021, https://doi.org/10.1029/2020gl092293), which showed widespread increases in the duration of drought events over the last five decades in the western United States. They point out that our decision to smooth the data using a moving average inflated the number of weather stations at which the trends toward longer droughts were deemed significant by a statistical test. We agree with them on this point, and we have recomputed all our results using unsmoothed data to determine the impacts. We find that for most stations and regions, trend magnitudes remained largely unchanged, with many stations nearby one another often suggesting similar trends. Finally, we agree with Paciorek and Wehner that there is a lack of statistical methods to test such coherent regional patterns, and we caution that over‐reliance on p‐values limits the power of regional data to identify important climate trends. Key Points: We agree that smoothing to 5‐year moving windows introduced serial correlation into time series of annual statistics of daily rainfall data, inflating the number of weather stations individually showing significant trends (p < 0.05) with the Mann‐Kendall testRecomputation with unsmoothed values produced substantially the same dry intervals trend magnitude and direction at most stations individually and had only minimal impacts on dry interval trends computed for National Ecological Observatory Network domains using the Regional Kendall testNo perfect statistical approach leverages the capacity of coherent regional patterns among spatially correlated weather stations, and an over‐reliance on p‐values as a binary (significant vs. insignificant) determinant of trends limits the power of regional data [ABSTRACT FROM AUTHOR]

Aim: As climate change increases the frequency and severity of droughts in many regions, conservation during drought is becoming a major challenge for ecologists. Droughts are multidimensional climate events whose impacts may be moderated by changes in temperature, water availability or food availability, or some combination of these. Simultaneously, other stressors such as extensive anthropogenic landscape modification may synergize with drought. Useful observational models for guiding conservation decision‐making during drought require multidimensional, dynamic representations to disentangle possible drought impacts, and consequently, they will require large, highly resolved data sets. In this paper, we develop a two‐stage predictive framework for assessing how drought impacts vary with species, habitats and climate pathways. Location: Central Valley, California, USA. Methods: We used a two‐stage counterfactual analysis combining predictive linear mixed models and N‐mixture models to characterize the multidimensional impacts of drought on 66 bird species. We analysed counts from the eBird participatory science data set between 2010 and 2019 and produced species‐ and habitat‐specific estimates of the impact of drought on relative abundance. Results: We found that while fewer than a quarter (16/66) of species experienced abundance declines during drought, nearly half of all species (27/66) changed their habitat associations during drought. Among species that shifted their habitat associations, the use of natural habitats declined during drought while use of developed habitat and perennial agricultural habitat increased. Main Conclusions: Our findings suggest that birds take advantage of agricultural and developed land with artificial irrigation and heat‐buffering microhabitat structure, such as in orchards or parks, to buffer drought impacts. A working lands approach that promotes biodiversity and mitigates stressors across a human‐induced water gradient will be critical for conserving birds during drought. [ABSTRACT FROM AUTHOR]

The accelerating pace of climate change has led to unprecedented shifts in surface temperature and precipitation patterns worldwide, with African savannas being among the most vulnerable regions. Understanding the impacts of these extreme changes on ecosystem health, functioning and stability is crucial. This paper focuses on the detection of breakpoints, indicative of shifts in ecosystem functioning, while also determining relevant ecosystem characteristics and climatic drivers that increase susceptibility to these shifts within the semi‐arid to arid savanna biome. Utilising a remote sensing change detection approach and rain use efficiency (RaUE) as a proxy for ecosystem functioning, spatial and temporal patterns of breakpoints in the savanna biome were identified. We then employed a novel combination of survival analysis and remote sensing time series analysis to compare ecosystem characteristics and climatic drivers in areas experiencing breakpoints versus areas with stable ecosystem functioning. Key ecosystem factors increasing savanna breakpoint susceptibility were identified, namely higher soil sand content, flatter terrain and a cooler long‐term mean temperature during the wet summer season. Moreover, the primary driver of changes in ecosystem functioning in arid savannas, as opposed to wetter tropical savannas, was found to be the increased frequency and severity of rainfall events, rather than drought pressures. This research highlights the importance of incorporating wetness severity metrics alongside drought metrics to comprehensively understand climate–ecosystem interactions leading to abrupt shifts in ecosystem functioning in arid biomes. The findings also emphasise the need to consider the underlying ecosystem characteristics, including soil, topography and vegetation composition, in assessing ecosystem responses to climate change. While this research primarily concentrated on the southern African savanna as a case study, the methodological robustness of this approach enables its application to diverse arid and semi‐arid biomes for the assessment of climate–ecosystem interactions that contribute to abrupt shifts. [ABSTRACT FROM AUTHOR]

Extensive dieback of salt marsh dominated by the perennial grass Spartina alterniflora occurred throughout the Mississippi River deltaic plain during 2000. More than 100,000 ha were affected, with 43,000 ha severely damaged. The aim of this work was to determine if sudden dieback could have been caused by a coincident drought and to assess the significance of this event with respect to long-term changes in coastal vegetation. Multiple dieback sites and reference sites were established along 150 km of shoreline in coastal Louisiana, USA. Aerial and ground surveys were conducted from June 2000 to September 2001 to assess soil conditions and plant mortality and recovery. Dieback areas ranged in size from ∼300 m2−5 km2 in area with 50–100% mortality of plant shoots and rhizomes in affected zones. Co-occurring species such as Avicennia germinans (black mangrove) and Juncus roemerianus (needlegrass rush) were unaffected. Historical records indicate that precipitation, river discharge, and mean sea level were unusually low during the previous year. Although the cause of dieback is currently unknown, plant and soil characteristics were consistent with temporary soil desiccation that may have reduced water availability, increased soil salinity, and/or caused soil acidification (via pyrite oxidation) and increased uptake of toxic metals such as Fe or Al. Plant recovery 15 months after dieback was variable (0–58% live cover), but recovering plants were vigorous and indicated no long-lasting effects of the dieback agent. These findings have relevance for global change models of coastal ecosystems that predict vegetation responses based primarily on long-term increases in sea level and submergence of marshes. Our results suggest that large-scale changes in coastal vegetation may occur over a relatively short time span through climatic extremes acting in concert with sea-level fluctuations and pre-existing soil conditions. [ABSTRACT FROM AUTHOR]

Alfalfa (Medicago sativa L.) plays an important role in livestock production in most regions of the world, but the quantity and quality of alfalfa have been critically affected by drought events in recent years. Thus, quantifying the efficacy of widely used strategies, irrigation methods and fertilization that are aimed at improving drought resistance in alfalfa is a worthy topic that has been addressed in a variety of ways using both field observations and simulation models. Although such strategies play a critical role in climate change adaptation, the global patterns of these strategies in a changing world remain elusive due to regional differences, such as drought features, strategy design and environmental conditions. Thus, by using effect size and statistical analyses, we synthesized three variables, namely, alfalfa yield, water use efficiency (WUE) and crude protein (CP), to examine the efficacy of irrigation methods and fertilization in drought areas based on peer‐reviewed papers from 1990 to 2022. Our results showed that increasing drought stress reduces the alfalfa yield (−34.4%) but can increase the WUE (+13.7%). Both yield and WUE showed a negative relationship with the water deficit, but this phenomenon can be improved by using appropriate irrigation. The yield losses of alfalfa can be offset by implementing a fertilization strategy (+22%) under drought stress, especially for phosphate fertilizer. Overall, our results provide some evidence for the climate change adaptation of alfalfa under drought stress and indicate that fertilization is a more effective adaptation to improve alfalfa drought resistance (both yield and WUE, and yield and CP) than the irrigation method, which shows better performance in improving alfalfa WUE. Our synthesis of the effectiveness of irrigation methods and fertilization on alfalfa drought resistance can be used to develop scientific strategies for climate change adaptation for alfalfa and agriculture under climate change. [ABSTRACT FROM AUTHOR]

Adverse climate changes in Pakistan undermine the water resources and give rise to transient and permanent droughts in different parts of the country. The occurrence of drought cannot be prevented, but its detrimental impacts can be brought down by proper pre‐drought planning. Effective planning owes to using scientific and probabilistic approaches. In this paper, the interarrival time of drought for seven operational drought indices in Pakistan is modelled by using the modified distribution of convolution derived from the Bivariate Affine Linear Exponential (BALE) distribution. A new stochastic variable, interarrival time of drought, is generated from the data of drought indices from 1951 to 2016 used in Pakistan by applying the theory of runs. The proposed model identifies Palmer drought severity index (PDSI) and Reconnaissance drought index (RDI) as the most appropriate meteorological indices for the under‐study country. The quantiles of the model are computed that provide information about the interarrival time of drought and help to anticipate this phenomenon. In addition, return periods for all the seven indices are calculated to report the frequency and duration of drought over a certain period. Finally, some recommendations for the National Drought Monitoring Centre (NDMC) and Pakistan Council of Research in Water Resources (PCRWR) are stated for better future planning to avoid the adverse impacts of drought. [ABSTRACT FROM AUTHOR]

Local governments have led the way on climate action in the United States. While the federal government has largely stood to the side, local governments have made great efforts to adopt policies aimed at reducing greenhouse gas emissions. A large and robust literature in urban politics has explored the variables that influence local government action on climate change in the United States. Issue severity and resident ideological preferences have been identified as two of the most important factors in local climate action. Governments that are more likely to face major impacts from climate, such as coastal communities, and governments serving more liberal residents have both been found to pursue climate policy at higher rates. In this paper we suggest that these relationships are better understood as conditional. We argue that the effect of issue severity will be moderated by ideology. When residents are liberal, issue severity will matter. When residents are conservative, the impact will be muted. We find strong evidence for this hypothesis. Coastal governments and governments that have experienced drought adopt more climate policies, but this is conditional on the ideology of residents. [ABSTRACT FROM AUTHOR]

The high‐mountain system, a storehouse of major waterways that support important ecosystem services to about 1.5 billion people in the Himalaya, is facing unprecedented challenges due to climate change during the 21st century. Intensified floods, accelerating glacial retreat, rapid permafrost degradation, and prolonged droughts are altering the natural hydrological balances and generating unpredictable spatial and temporal distributions of water availability. Anthropogenic activities are adding further pressure onto Himalayan waterways. The fundamental question of waterway management in this region is therefore how this hydro‐meteorological transformation, caused by climate change and anthropogenic perturbations, can be tackled to find avenues for sustainability. This requires a framework that can diagnose threats at a range of spatial and temporal scales and provide recommendations for strong adaptive measures for sustainable future waterways. This focus paper assesses the current literature base to bring together our understanding of how recent climatic changes have threatened waterways in the Asian Himalayas, how society has been responding to rapidly changing waterway conditions, and what adaptive options are available for the region. The study finds that Himalayan waterways are crucial in protecting nature and society. The implementation of integrated waterways management measures, the rapid advancement of waterway infrastructure technologies, and the improved governance of waterways are more critical than ever. This article is categorized under:Engineering Water > Sustainable Engineering of Water [ABSTRACT FROM AUTHOR]

Water played an undeniably significant role in the origins of complex societies across the Near East, but political complexity in regions like Southeast Arabia diverges dramatically from the more well‐known histories of Egypt, the Levant and Mesopotamia. Through quantitative analysis, this paper investigates spatial associations between water availability and Umm an‐Nar towers in Adh Dhahirah Governorate of Oman. We hypothesise that ancient Umm an‐Nar people targeted high water flow accumulation areas for major settlements with towers. Our results lead us to reject the null hypothesis of no spatial association between tower settlements and water and help clarify the role of water in the rise of complex polities. [ABSTRACT FROM AUTHOR]

The water table depth (WTD) in peatlands determines the soil carbon decomposition rate and influences vegetation growth, hence the above‐ground carbon assimilation. Here, we used satellite‐observed Solar‐Induced chlorophyll Fluorescence (SIF) as a proxy of Gross Primary Production (GPP) to investigate water‐related vegetation stress over northern peatlands. A linear model with interaction effects was used to relate short‐ and long‐term anomalies in SIF with WTD anomalies and the absolute WTD. Most locations showed the occurrence of drought and waterlogging stress though regions with exclusively waterlogging or drought stress were also detected. As a spatial median, minimal water‐related vegetation stress was found for a WTD of −0.22 m (short‐term) and −0.20 m (long‐term) (±0.01 m, 95% confidence interval of statistical uncertainty). The stress response observed with SIF is supported by an analysis of in situ GPP data. Our findings provide insight into how changes in WTD of northern peatlands could affect GPP under climate change. Plain Language Summary: Water table depth is an important variable influencing the carbon cycle and vegetation growth in northern peatlands. In this paper, the impact of changing wetness conditions on vegetation growth over peatlands was studied through satellite measurements of solar‐induced fluorescence (SIF), which is a radiation signal emitted by vegetation during photosynthesis. Previous studies over ecosystems on mineral soil, that is, not over peatland, suggested a response of SIF to drought conditions. In our study, it was shown that peatland vegetation experiences moisture‐related growth stress under both very wet and very dry conditions, which might reduce the photosynthesis efficiency and the ability to capture and store CO2. Stress due to drought conditions was detected for peatlands in the south of the Western Siberian Lowlands and the Boreal Plains. Stress due to prolonged wet conditions occurred for example, in the north of the Western Siberian Lowlands and the north of the Hudson Bay Lowlands. Key Points: Spaceborne Solar‐Induced Fluorescence (SIF) data was used to analyze soil moisture‐related vegetation stress regimes in northern peatlandsFor most locations, waterlogging as well as drought stress regimes occurred and alternated depending on peatland water level dynamicsThe SIF‐based stress response observations are supported by in situ data of Gross Primary Production [ABSTRACT FROM AUTHOR]

The article provides literary figure John Spencer's arguments defending his enclosures in his works. The commodities of pasture and considerations shown in the article prove that it is necessary to have them. In primus by enclosure there is fat iovys and moutons two times a year which cannot be past once a year in no fallow field in the best year and some fallow fields which are none. In one item of enclosure there is great breed of sheep. And the ewes going in pasture spend little hay or none by reason of coming after the danger of winter pasture. In another item when the great rain comes or great drought or other unreasonable weather the pasture sheep enjoy. In another item it is elaborated that to make new houses is not requisite for there is more houses than there be men to dwell in them in many villages and towns except in places nigh to the sea coast or the City of London in England. Another item argues that the Statutes of Laborers may be better in Execution than they have been.

Tree rings have been central to the understanding of variability of flow of the Colorado River. Spurred by steadily declining flows after the 1920s, early tree‐ring research drew attention to the importance of climate variability to water supply by identifying episodes in the past that were even drier. Application of modern statistical methods to tree‐ring data later yielded a reconstruction of annual flows at Lees Ferry back to the early 1500s that highlighted the unprecedented wetness of the base period for the 1922 Colorado River Compact. That reconstruction served as the framework for a collection of papers in a 1995 special issue of Water Resources Bulletin on coping with severe sustained drought on the Colorado River. This retrospective paper reviews historical aspects of the dendrohydrology of the Colorado River, and the updates since 1995. A constantly expanding tree‐ring network has been subjected to an array of new statistical approaches to reconstruction. Climate change and increasing demand for water have meanwhile driven increased interest in the processing and presentation of reconstructions for optimal use in water resources planning and management. While highlighting the robustness of main findings of earlier studies, recent research yields improved estimates of magnitudes of flow anomalies, extends annual flows to more than 1200 years, and underscores unmatched drought duration in the medieval period. [ABSTRACT FROM AUTHOR]

Summary: A surge of papers have reported low leaf vulnerability to xylem embolism during drought. Here, we focus on the less studied, and more sensitive, outside‐xylem leaf hydraulic responses to multiple internal and external conditions. Studies of 34 species have resolved substantial vulnerability to dehydration of the outside‐xylem pathways, and studies of leaf hydraulic responses to light also implicate dynamic outside‐xylem responses. Detailed experiments suggest these dynamic responses arise at least in part from strong control of radial water movement across the vein bundle sheath. While leaf xylem vulnerability may influence leaf and plant survival during extreme drought, outside‐xylem dynamic responses are important for the control and resilience of water transport and leaf water status for gas exchange and growth. [ABSTRACT FROM AUTHOR]

There is a need to support applied, community‐relevant hydrologic research within changing climate, population, and socioeconomic conditions to better inform water policy and management. We hypothesized that providing a rural agricultural community in a semiarid valley with the necessary monitoring tool to meet local water management needs would increase adaptive capacity within the context of long‐term drought. Through a community science approach, researchers installed a telemetry monitoring system at participating acequia irrigation diversions that remotely sent water data to a web interface every 15 min. Two surveys distributed before and after web interface access targeted seven adaptive capacity indicators. After the first season of improved data accessibility, the following adaptive capacity indicators significantly increased: information diversity, cognitive social capital, leadership, and proactivity. Rather than focusing on the water savings aspect of real‐time monitoring, this paper summarizes a novel water resources study that assessed the social impact of real‐time irrigation water delivery monitoring on adaptive capacity. This study suggests that bridging the gap between community need and hydrologic research through community science, sociologic analysis, and stakeholder engagement provides significant benefits for communities facing water management challenges, further supporting problem‐driven water resources research. [ABSTRACT FROM AUTHOR]

Drought seriously endangers the development of agro‐pastoral ecotone in arid and semi‐arid regions. However, drought evolution characteristics of semi‐arid sandy grassland and its drivers are not well understood in the complex climate change context. Thus, in this paper, the revised standardized precipitation evaporation indices on one‐month (SPEI‐1) and growing‐season (SPEI‐6) scale, flash drought and dry spells (DS) were calculated as drought indicators, and the temporal variabilities and meteorological drivers of drought in Horqin Sandy Land during the growing period (April–September) from 2007 to 2021 were studied. The results showed that SPEI‐1 and SPEI‐6 exhibited negative trends and periodic change. This drought aggravation was manifested in increased grades and numbers of drought months. Flash droughts can occur every month during the growing season. And its occurrence was not only positively correlated with all drought events in frequency but also synchronized in time. The increased number of DS showed an asymmetrical shift towards 7‐day‐and‐longer DS. SPEI sensitivity to precipitation (P) was noticeably higher than to atmospheric evapotranspiration demand (AED) at both monthly and growing season scales. SPEI sensitivity to AED was modulated by P amounts, which was higher during low P period. Apart from the amounts of P and AED, their temporal variability also strongly determined how they affect the drought severity. P was also the main driver for flash drought and long DS, but AED with larger amount and higher variability is the reason for their aggravation. Our results demonstrate the complexity of drought intensification in semi‐arid sandy grasslands and highlight the important role of AED anomalies in it. [ABSTRACT FROM AUTHOR]

Recovering additional historical weather observations from known archival sources will improve the understanding of how the climate is changing and enable detailed examination of unusual events within the historical record. The UK National Meteorological Archive recently scanned more than 66,000 paper sheets containing 5.28 million hand‐written monthly rainfall observations taken across the UK and Ireland between 1677 and 1960. Only a small fraction of these observations were previously digitally available for climate scientists to analyse. More than 16,000 volunteer citizen scientists completed the transcription of these sheets of observations during early 2020 using the RainfallRescue.org website, built using the Zooniverse platform. A total of 3.34 million observations from more than 6000 locations have so far been quality controlled and made openly available. This has increased the total number of monthly rainfall observations that are available for this time period and region by a factor of six. The newly rescued observations will enable longer and much improved reconstructions of past variations in rainfall across the British and Irish Isles, including for periods of significant flooding and drought. Specifically, this data should allow the official gridded monthly rainfall reconstructions for the UK to be extended back to 1836, and even earlier for some regions. [ABSTRACT FROM AUTHOR]

Tree diversity and species identity are known to play an important role in modulating forest productivity and its capacity to buffer the effects of climatic events. The FunDivEurope exploratory platform allowed us to analyse this modulating effect in a medium‐term time span, after an abrupt rise to a new stable level of the average summer temperature of ca 2°C, in Mediterranean forests in central Italy. This paper aims to answer the following questions: 1) did increasing temperature and drought events affect the growth of thermophilous deciduous forests? 2) Was this effect buffered in mixed stands compared to monocultures? 3) Did co‐occurring tree species with different ecological characteristics, from more mesophilous to more xerophilous, have different responses? In 2012 and 2017, wood cores were collected from 659 trees in 36 plots representative of thermophilous deciduous forests. The selected tree species were Castanea sativa, Ostrya carpinifolia, Quercus cerris, Quercus ilex and Quercus petraea. In the sampling plots, they were present in pure stands and mixtures from two to four species. After measuring annual rings on cores, chronologies of basal area increment were built, and inventory data were used to estimate tree growth. Results showed a strong reduction of growth, lasting at least 18 years, after the temperature rise. Tree diversity significantly reduced the growth drop after the sudden and stable rise in summer average temperature. Tree mixture effect on growth stability appeared to be dependent on the tree species present in the mixture. Temperature rise and associated drought events, even without changes in rainfall, are one of the main challenges that European forests will face in the current scenarios of climate change. Tree diversity can buffer the effects of climate change over periods of at least 15 years and should be considered in forest management plans. [ABSTRACT FROM AUTHOR]

This exploratory study proposes an original intra‐life history investigation through sequential analysis of the isotopic composition of carbon, nitrogen, and sulfur (CNS) on both primary and secondary dentin of a tooth (M1). We focus on an elderly woman from Longobard Italy (6th to 8th c. CE), who showed an unprecedented case of cranial surgery, presented in a companion paper by Micarelli and colleagues. Sequential stable CNS isotope composition of first molar dentin collagen allows us to infer diet, mobility, health, and physiological stress between approximately 3 months after birth to 9.5 years old (primary dentin) and between early adulthood until death (secondary dentin). Isotopic results on primary dentin highlight the following: (i) a long weaning period (ending at approximately 4 years), followed by (ii) a specific diet, including the contribution of C4 crops in early childhood (approximately 5.5 years), possibly concomitant with mobility. While secondary dentin shows a generally homogeneous diet during adulthood, the longitudinal analysis provided information on specific stresses that likely occurred in periods of difficult health conditions. This work emphasizes the importance of measuring complete dentin sequences (including secondary when present) for isotopic analysis to broaden intra‐life histories in ancient populations. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive picture of extreme precipitation across Nepal from 1976 to 2015 based on high‐quality daily precipitation observations from 28 precipitation stations spatially distributed across the country. We computed 11 extreme precipitation indices. The selected indices allow the analysis of extreme events (such as flood/inundation) related to heavy precipitation and evaluate the linkage with indications of agricultural production and drought (such as consecutive dry and wet days). Using a simple daily intensity index (SDII) and the number of days with daily precipitation ≥10 mm (R10), along with the total amount of annual precipitation (PRCPTOT), we summarized the distribution of the wet periods of the year at different locations. We divided the study period into two halves (T1: 1976–1995 and T2: 1996–2015) to examine the temporal mean, trends, and their shift. We emphasized the changes in those indices between these two periods across the country. Our results show that although the amount of precipitation (in terms of PRCPTOT and SDII) did not change significantly between the two periods (i.e., T1 and T2), there exists a clearly increasing trend of extreme precipitation indices in T2 compared to T1. In addition, the consecutive dry days show the rising tendency of elongated dry spells that can adversely affect plant/crop growth in the future. Our study recommends the need for effective management of both precipitation extremes (i.e., drier and wetter), for instance, by introducing irrigation facilities and flood mitigation measures. Plain Language Summary: We computed different precipitation indices using daily data from 28 precipitation stations spatially distributed across Nepal to obtain a clear picture of extreme precipitation from 1976 to 2015. We divided the study period into two halves of 20 years each. This study emphasizes the changes in magnitudes and trends of extreme precipitation between the two periods. Overall, we find that heavy precipitation indices increased significantly in the later period. Notably, dry spells (i.e., no rainfall) for consecutive days showed a remarkably increasing trend. Our results indicate the need for mitigation of this extreme precipitation to prevent both floods and drought. Key Points: We divide the study period (1976–2015) into two halves to analyze precipitation patterns and their shiftWe emphasize changes in the precipitation indices across the country between the two periodsWe find a clearly increasing trend of extreme precipitation indices in the recent period when compared to the earlier one [ABSTRACT FROM AUTHOR]

This paper analyses extreme meteorological droughts in the territory of the Pannonian Basin in central and southeastern Europe. Droughts are treated from an agricultural perspective as periods of consecutive days with very little or no rainfall at all. By using data from the historical period 1981–2010, time intervals longer than 20 days with less than 3 mm per day during the growing season April–September are examined to determine theoretical and empirical distributions of their number and durations. Related discrete stochastic process of extremes is analysed by the Zelenhasic–Todorovic (ZT) method, successfully applied in hydrology and meteorology (e.g., peak flows, low flows, meteorological droughts, etc.). The method is applied to 52 locations across Pannonia Basin. At each location, the Poisson distribution is determined for the number of droughts, exponential distribution for the duration of droughts, and double exponential distribution for the duration of the (annually) longest droughts. To validate the quality of modelling and the results obtained, standard statistical goodness of fit tests are used. Historical data from the period 1981–2010 indicate that the central and northern part of Hungary and the entire territory of Vojvodina Province in the north of Serbia experienced the longest droughts, on average 55–60 days. In statistical terms, across Pannonia Basin once in 100 years drought may occur with an average duration of 56 days. Theoretically longest 100‐year droughts could be expected in the northern part of Hungary (up to 70 days), the eastern part of Romania (up to 68 days), and Serbia (up to 69 days). The 2‐year droughts are on the average duration of 3 weeks. Generated maps of the longest droughts in the basin may help to reduce agricultural risks due to global warming and other negative impacts of climate change. [ABSTRACT FROM AUTHOR]

They note that while it is common to study effects of drought on water flows, drought effects on water quality and, subsequently, on ecosystems are often ignored. Featured Collection introduction: Severe sustained drought revisited managing the Colorado River system in times of water shortage 25 years later - Part II The call for papers for the I JAWRA i Featured Collection: Severe Sustained Drought Revisited: Managing the Colorado River System in Times of Water Shortage 25 Years Later led to more insights than could fit into a single issue. The article by Salehabadi et al. ([11]) quantifies the impacts of three drought scenarios based on three past sustained droughts. [Extracted from the article]

Climate change is increasing the severity and frequency of droughts around the globe, leading to tree mortality that reduces production and provision of other ecosystem services. Recent studies show that growth of mixed stands may be more resilient to drought than pure stands. The two most economically important and widely distributed tree species in Europe are Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.), but little is known about their susceptibility to drought when coexist.This paper analyses the resilience (resistance, recovery rate and recovery time) at individual‐tree level using a network of tree‐ring collections from 22 sites along a climatic gradient from central Europe to Scandinavia. We aimed to identify differences in growth following drought between the two species and between mixed and pure stands, and how environmental variables (climate, topography and site location) and tree characteristics influence them.We found that both the timing and duration of drought drive the different responses between species and compositions. Norway spruce showed higher vulnerability to summer drought, with both lower resistance and a longer recovery time than Scots pine. Mixtures provided higher drought resistance for both species compared to pure stands, but the benefit decreases with the duration of the drought. Especially climate sensitive and old trees in climatically marginal sites were more affected by drought stress.Synthesis. Promoting Scots pine and mixed forests is a promising strategy for adapting European forests to climate change. However, if future droughts become longer, the advantage of mixed stands could disappear which would be especially negative for Norway spruce. [ABSTRACT FROM AUTHOR]

In this paper, we report on the frequency of false onsets of wet season rainfall in the case of the Northern Australian wet season and investigate the role of large‐scale tropical climate processes such as the El Niño–Southern Oscillation, Indian Ocean Dipole (IOD) and Madden–Julian Oscillation. A false onset occurs when a wet season rainfall onset criterion is met, but follow‐up rainfall is not received for weeks or months later. Our analysis of wet season rainfall data from 1950 through 2020 shows a false onset occurs, on average, between 20 and 30% of wet seasons across all of northern Australia. This increases at a regional and local level such as at Darwin, the Northern Territory (NT), and parts of Queensland's north coast to over 50%. Seasonal climate influences, such as a La Niña pattern and a negative IOD that typically expedite the wet season rainfall onset, also increase the likelihood of a false onset over northern Australia. Our analysis also finds that periods of false onsets can sometimes, but not always, coincide with periods of rapid soil moisture depletion. The false rainfall onsets that develop into flash drought can be potentially disruptive and costly and are of potential significance for agriculture and fire management in northern Australia, and in other monsoonal climates that also typically experience a slow build‐up to the seasonal monsoon. In conclusion, effective rainfall indicates that many seasons experience 'false onsets' with dry conditions after early rainfall. We propose that false onsets are a physical characteristic of the climate of northern Australia which occurs with relatively high frequency. In addition, these false onsets may sometimes co‐occur with a flash drought. [ABSTRACT FROM AUTHOR]

Responding to disasters triggered by natural hazards is a deeply political process, but it is usually presented by practitioners as an apolitical endeavour. This is striking when disasters occur in authoritarian and politically highly polarised conflict‐affected settings. Although the literature provides leads as to why and how humanitarians depoliticise aid, there has been little empirical research on the implications of depoliticisation, especially at the community level. Based on qualitative fieldwork that focused on the drought responses that overlapped with the 2016–19 sociopolitical crises in Zimbabwe, this paper details the practices, motivations, and implications of humanitarian depoliticisation. It differentiates between strategic, coerced, and routine managerial depoliticisation, and argues that, in an authoritarian conflict‐affected setting, depoliticisation strategically allows state and non‐state actors to defuse sensitive issues and actor relations and to remain safe. However, depoliticisation can also have implications for information management, monitoring, accountability, and protection, and thus ultimately for upholding humanitarian principles. [ABSTRACT FROM AUTHOR]

Knowledge of drought resistance of cool‐season turfgrasses is important because drought stress can occur wherever they are grown even in humid regions with wet climates. This review is Part II of two companion papers that review water use and requirements in cool‐season turfgrasses. Part I presented the history of early water conservation and quantification methods in turfgrass and then summarized research results since 1980 on cool‐season turfgrass evapotranspiration and deficit irrigation. Part II presents a brief history of drought research and then summarizes studies completed since 1980 on cool‐season turfgrass drought resistance including interspecies and intraspecies differences. This overview of research regarding drought resistance covers >30 field experiments that evaluated drought response to irrigation amounts, length of dry down, and the influence of environmental and management factors. More cool‐season turf research has focused on intraspecies variation in drought resistance of Kentucky bluegrass (Poa pratensis L.) or tall fescue (Festuca arundinacea Schreb.) than any other cool‐season turf species; therefore, more research is needed on other cool‐season turfgrass species, such as perennial ryegrass (Lolium perenne L.), bentgrasses (Agrostis L. ssp.), and fine fescues (Festuca L. spp.). Further study is warranted to investigate differences in drought resistance strategies among plants and management practices, shoot and root responses, subsequent recovery, and inter‐ and intraspecies variation in cool‐season turfgrasses especially in northern climatic regions where cool‐season turf species are adapted. Improvement of drought resistance in cool‐season turfgrasses will require focused breeding efforts with acute drought screening protocols. [ABSTRACT FROM AUTHOR]

Summary: Drought is intensifying globally with climate change, creating an urgency to understand ecosystem response to drought both during and after these events end to limit loss of ecosystem functioning. The literature is replete with studies of how ecosystems respond during drought, yet there are far fewer studies focused on ecosystem dynamics after drought ends. Furthermore, while the terms used to describe drought can be variable and inconsistent, so can those that describe ecosystem responses following drought. With this review, we sought to evaluate and create clear definitions of the terms that ecologists use to describe post‐drought responses. We found that legacy effects, resilience and recovery were used most commonly with respect to post‐drought ecosystem responses, but the definitions used to describe these terms were variable. Based on our review of the literature, we propose a framework for generalizing ecosystem responses after drought ends, which we refer to as 'the post‐drought period'. We suggest that future papers need to clearly describe characteristics of the imposed drought, and we encourage authors to use the term post‐drought period as a general term that encompasses responses after drought ends and use other terms as more specific descriptors of responses during the post‐drought period. [ABSTRACT FROM AUTHOR]

Kenya is prone to severe droughts due to infrequent, unpredictable and irregular annual precipitation in many parts of the country. Of all 47 Kenyan counties, 23 are classified as arid and semi‐arid (ASAL), constituting approximately 88% of the country's land mass. Like in many developing countries, droughts in Kenya are well known to affect provision of food. They also have the potential to affect infrastructure services. Kenya has an infrastructure deficit, meaning that a large portion of the infrastructure has not been significantly developed, being exposed to major risks emanating from natural disasters. When droughts occur, infrastructure is exposed to further risks of structural damage and deterioration, leading to increased maintenance costs. In addition, users must travel longer distances and spend more time in order to have access to infrastructure services. This paper discusses how droughts affect users of infrastructure services. The survey is based on a primary study carried out in 1370 households across 27 counties of Kenya. It also relies on secondary data, including from the Kenya Integrated Household Budget Survey (KIHBS) for 2015/16, reflecting access to basic infrastructure services across the surveyed 27 counties. The research findings illustrate that droughts reduce access to infrastructure services such as energy, water provision, housing and communications, thus requiring climate‐sensitive policy interventions. The study concludes that building resilient infrastructure to respond to and mitigate the effects of drought is critical. It also emphasizes the importance of cooperation among different stakeholders in the country. [ABSTRACT FROM AUTHOR]

Drought events occur worldwide and possibly incur severe consequences. Trying to understand and characterize drought events is of considerable importance in order to improve the preparedness for coping with future events. In this paper, we present a methodology that allows for the delineation of drought events by exploiting their spatiotemporal nature. To that end, we apply operators borrowed from mathematical morphology to represent drought events as connected components in space and time. As an illustration, we identify drought events on the basis of a 35‐year data set of daily soil moisture values covering mainland Australia. We then extract characteristics reflecting the affected area, duration and intensity from the proposed representation of a drought event in order to illustrate the impact of tuning parameters in the methodology presented. Yet, this paper we refrain from comparing with other drought delineation methods. [ABSTRACT FROM AUTHOR]

Drought, widely studied as an important driver of ecosystem dynamics, is predicted to increase in frequency and severity globally. To study drought, ecologists must define or at least operationalize what constitutes a drought. How this is accomplished in practice is unclear, particularly given that climatologists have long struggled to agree on definitions of drought, beyond general variants of "an abnormal deficiency of water." We conducted a literature review of ecological drought studies (564 papers) to assess how ecologists describe and study drought. We found that ecologists characterize drought in a wide variety of ways (reduced precipitation, low soil moisture, reduced streamflow, etc.), but relatively few publications (~32%) explicitly define what are, and are not, drought conditions. More troubling, a surprising number of papers (~30%) simply equated "dry conditions" with "drought" and provided little characterization of the drought conditions studied. For a subset of these, we calculated Standardized Precipitation Evapotranspiration Index values for the reported drought periods. We found that while almost 90% of the studies were conducted under conditions quantifiable as slightly to extremely drier than average, ~50% were within the range of normal climatic variability. We conclude that the current state of the ecological drought literature hinders synthesis and our ability to draw broad ecological inferences because drought is often declared but is not explicitly defined or well characterized. We suggest that future drought publications provide at least one of the following: (a) the climatic context of the drought period based on long‐term records; (b) standardized climatic index values; (c) published metrics from drought‐monitoring organizations; (d) a quantitative definition of what the authors consider to be drought conditions for their system. With more detailed and consistent quantification of drought conditions, comparisons among studies can be more rigorous, increasing our understanding of the ecological effects of drought. [ABSTRACT FROM AUTHOR]

Background: Use of soil amendments in agriculture is an old practice and with increase in demand of organic agriculture, it is gaining more attention. Work on the quality of the produce more particularly if crop faces any adverse situation like drought are scarce. This paper provides a comparative assessment of organic (farm yard manure) and inorganic (biochar) soil amendments on grain quality of grass pea (Lathyrus sativus L.) when crop faces drought. Different grain quality parameters were studied along with crop health and grain yield under the application of soil amendments during drought. Results: Biochar and farm yard manure (FYM) lowered drought‐induced leaf water potential (upto 22%) and root nitrate reductase activity (by 62% and 67% respectively). Both inorganic and organic soil amendments improved in vitro protein digestibility (up to 16% and 37% respectively). Whereas higher grain phytic acid content (increased up to 40%) was noted from application of organic amendment (FYM) compared to inorganic (16% increase in biochar treated plots). Protein yield is enhanced (8%) under the application of Biochar‐enhanced protein yield by 8% when crops experienced drought at vegetative stage, whereas FYM reduced it by 9% under the same situation. Conclusion: Tested soil amendments can improve grain quality of grass pea. However, they were not equally efficient when the crop experienced drought at either stage of growth. Thus, screening of soil amendment is important when added under stressful situation like drought to ascertain better grain quality for consumers. [ABSTRACT FROM AUTHOR]

Combining ability effects for yield related traits can serve as selection criteria to pursue breeding for optimal biomass allocation in wheat (Triticum aestivum). The objective of this paper is to provide information based on a retrospective quantitative genetic analysis on combining ability studies of wheat for yield and yield‐related traits to predict potential genetic gains achievable in improving biomass allocation for drought tolerance and soil carbon storage. The study compares data on the general combining ability and specific combining ability effects of wheat for yield and related traits under optimum and drought stressed conditions from 40 studies around the world. Days to heading (DTH), plant height (PH), number of tillers per plant (TN), kernels per spike (KPS), 1,000‐kernel weight (TKW), shoot biomass (SB), and grain yield (GY) exhibited wide variation for general combining ability (GCA) and specific combining ability effects. Progeny performance increased by 14.30 and 4.04% for SB and GY, respectively, compared with parental values under optimum water conditions. Number of tillers and SB exhibited positive associations with GY (.45 ≤ r ≤.85, p <.05) under both water conditions. Meta effect sizes for drought stress were negative. The highest meta‐effect sizes were calculated for DTH (−4.5) followed by SB (−2.0), whereas KPS (−1.25) had the lowest. The genetic gains for PH, SB, and other yield components showed that divergent crosses involving complementary parents could enhance biomass allocation patterns in wheat. This could be used as a basis for improving biomass allocation to roots. Core Ideas: There is sufficient genetic variation in wheat genotypes for manipulating biomass allocation.The number of kernels per spike is stable under varying moisture conditions.Shoot biomass and grain yield expression are severely confounded by drought.Aboveground traits are important for indirect selection of root traits. [ABSTRACT FROM AUTHOR]

Maintaining a steady increase of yields requires knowledge of plant stress physiology and modern techniques of quantitative data collection and analysis. Here, the chlorophyll fluorescence parameters are used for modelling of relative water content (RWC) in field‐grown wheat cultivars. RWC is commonly used for the detection of plant tolerance to temporary droughts, but its determination is laborious and does not meet the requirements of a mass test like fluorescence detection. The paper presents a beta generalized linear mixed model (GLMM) fitted for RWC prediction based on chlorophyll fluorescence data repeatedly measured over time. The nature of fluorescence parameters with the strong correlations between them leads to the use of a multilevel principal component analysis to overcome this issue prior to the fitting of the model. Furthermore, a beta generalized estimating equation (GEE) model is fitted for identifying population‐average effects of the parameters used. Finally, highly significant results in terms of prediction with the use of 10‐fold cross‐validation (RPearson‐CV = 0.86, MAECV = 0.0365, RMSECV = 0.048) were obtained. Moreover, the population‐average effects provide important information for the parameters used in RWC prediction. The beta GLMM can provide good predictions combined with important cultivar‐specific information. Conclusively, these implementations can be a useful tool for drought tolerance improvement. [ABSTRACT FROM AUTHOR]

In discussions of extreme weather trends, the subject of atmospheric blocking remains an open question, in part because of the inability of climate models to accurately reproduce blocking frequency patterns for the current climate. A number of factors have been proposed to explain this failure, including specific problems with model physics and inadequate resolution. In this paper, we show that, in the case of the National Center for Atmospheric Research Community Atmosphere Model (NCAR CAM), its underestimation of blocking frequency is caused by its mean state bias and that correcting that bias increases blocking frequency estimates over Europe and decreases the root‐mean‐square error versus reanalysis from 0.015 to 0.011. Plain Language Summary: Atmospheric blocking events are long‐lasting weather formations that can cause destructive droughts, heat waves, or flooding. However, they are often underestimated in leading climate models, which means that predictions about how common blocking will be in a changing climate are unreliable. We applied an algorithm to the model that caused it to more closely resemble the observed climate and saw improved blocking estimates, suggesting that the cause of this underestimation is the failure of the model to precisely reproduce the climatological mean state of the real atmosphere, and that improvements in blocking estimates will come from eliminating these biases in the model. With better estimates, we will be better able to predict how the frequency of blocks–and the extreme weather that accompanies them–will change in the future. Key Points: Blocking frequency is often underestimated in climate models, including in the Community Atmosphere ModelImproving the moist parametrization by switching to a super‐parametrized version increases the root‐mean‐square error versus reanalysisCorrecting the bias in model mean state improves blocking frequency estimates, decreasing the error versus reanalysis from 0.015 to 0.011 [ABSTRACT FROM AUTHOR]

In discussions of extreme weather trends, the subject of atmospheric blocking remains an open question, in part because of the inability of climate models to accurately reproduce blocking frequency patterns for the current climate. A number of factors have been proposed to explain this failure, including specific problems with model physics and inadequate resolution. In this paper, we show that, in the case of the National Center for Atmospheric Research Community Atmosphere Model (NCAR CAM), its underestimation of blocking frequency is caused by its mean state bias and that correcting that bias increases blocking frequency estimates over Europe and decreases the root‐mean‐square error versus reanalysis from 0.015 to 0.011. Plain Language Summary: Atmospheric blocking events are long‐lasting weather formations that can cause destructive droughts, heat waves, or flooding. However, they are often underestimated in leading climate models, which means that predictions about how common blocking will be in a changing climate are unreliable. We applied an algorithm to the model that caused it to more closely resemble the observed climate and saw improved blocking estimates, suggesting that the cause of this underestimation is the failure of the model to precisely reproduce the climatological mean state of the real atmosphere, and that improvements in blocking estimates will come from eliminating these biases in the model. With better estimates, we will be better able to predict how the frequency of blocks–and the extreme weather that accompanies them–will change in the future. Key Points: Blocking frequency is often underestimated in climate models, including in the Community Atmosphere ModelImproving the moist parametrization by switching to a super‐parametrized version increases the root‐mean‐square error versus reanalysisCorrecting the bias in model mean state improves blocking frequency estimates, decreasing the error versus reanalysis from 0.015 to 0.011 [ABSTRACT FROM AUTHOR]

Investigating plant morphological traits can provide insights into plant drought tolerance. To date, many papers have focused on plant hydraulic responses to drought during dehydration, but atmospheric water absorption by trichomes to mitigate drought stress by influencing leaf hydraulics in plant species that inhabit arid environments has been largely ignored. The experiment in this study was designed to assess how dew absorbed by leaf trichomes helps Caragana korshinskii withstand drought. The results showed that under a drought stress and dew (DS & D) treatment, C. korshinskii displayed a strong capacity to absorb dew with trichomes; exhibited slow decreases in leaf water potential (Ψleaf), leaf hydraulic conductivity (Kleaf), and gas exchange; experienced 50% Kleaf and gas exchange losses at lower relative soil water content levels than plants treated with drought stress and no dew (DS & ND); and experienced 50% Kleaf loss (Kleaf P50) at similar Ψleaf levels as DS & ND plants. Its congener C. sinica, which does not have leaf trichomes, displayed little ability to absorb dew under drought stress and did not show any remarkable improvement in the above parameters under the DS & D treatment. Our results indicated that leaf trichomes are important epidermal dew-uptake structures that assist in partially sustaining the leaf hydraulic assimilation system, mitigate the adverse effects of drought stress and contribute to the distribution of C. korshinskii in arid environments. [ABSTRACT FROM AUTHOR]

Amazon tropical forests and the semiarid Northeast Brazil (NEB) region have registered very severe droughts during the last two decades, with a frequency that may have exceeded natural climate variability. Severe droughts impact the physiological response of Amazon forests, decreasing the availability to absorb atmospheric CO2, as well as biodiversity and increasing risk of fires. Droughts on this region also affect population by isolating them due to anomalous low river levels. Impacts of droughts over NEB region are related to water and energy security and subsistence agriculture. Most drought episodes over Amazonia and NEB are associated with El Niño (EN) events, anomalous warming over the Tropical North Atlantic (TNA), and even an overlapping among them. However, not all the dry episodes showed a large‐scale pattern linked to a canonical EN event or warm TNA episodes. For instance, dry episodes linked to EN events present distinct spatial patterns of precipitation anomalies depending on EN type (Central‐Pacific vs. Eastern‐Pacific EN), and NEB region experienced a severe drought in 2012 that is not attributed to EN or warm TNA events. Even in the case of the strong EN in 2015/16, some regional impacts have not been explained by EN contribution. This paper discusses the effects of CP and EP EN events, and the role of warm TNA events on tropical Walker and Hadley circulation leading to drought over Amazonia and NEB regions. [ABSTRACT FROM AUTHOR]

China has lots of funds, materials, and human resources in cloud seeding operations to help with water shortage problems across the country. But there is little guide about when and where the operations would obtain better benefits. To fill this gap, the modified Water Utilization Level (WUL) map of China mainland was plotted with the acquirable water utilization data on sub‐watershed scales in this study. Then the agricultural drought levels map of different counties were integrated with the modified WUL Map under preset rules to generate an integrated water scarcity map. Lastly, the cloud seeding demand maps of different seasons were drawn by integrating the agricultural drought seasons map of different counties with the integrated water scarcity map and the modified WUL map. Results showed that the middle north of China should have the highest priorities for cloud seeding operations during spring and summer, and some regions at the south during winter and spring, a few scattered regions at the northwest during spring and summer and a few regions at the middle of southeast China during summer and autumn should also have high priorities of cloud seeding operations. This research can help rain enhancement operations to obtain better effects on easing water scarcity problems and deepen the cooperation of water resources department and weather modification department in China. The designed intersecting rules of different maps in this paper also might inspire other relevant researches. Key Points: The results gave a clear demand from water resources field to weather modification department in China mainlandThe middle north areas of China have the severest water scarcity problems, especially during spring and summerSome less developed regions at the south, the northwest and the southeast have high water scarcity levels in different seasons [ABSTRACT FROM AUTHOR]

Summary: The circadian clock plays essential roles in diverse plant biological processes, such as flowering, phytohormone biosynthesis and abiotic stress responses. The manner in which circadian clock genes regulate drought stress responses in model plants has been well established, but comparatively little is known in crop species, such as soybean, a major global crop. This paper reports that the core clock components GmLHYs, the orthologues of CCA1/LHY in Arabidopsis, negatively control drought tolerance in soybean.The expressions of four GmLHYs were all induced by drought, and the quadruple mutants of GmLHYs demonstrated significantly improved drought tolerance. Transcriptome profiling suggested that the abscisic acid (ABA) signaling pathway is regulated by GmLHYs to respond to drought tolerance.Genetic dissections showed that two homologous pairs of LHY1a and LHY1b redundantly control the drought response. Functional characterization of LHY1a and LHY1b in Arabidopsis and soybean further supported the notion that GmLHYs can maintain cellular homeostasis through the ABA signaling pathway under drought stress.This study improves our understanding of the underlying molecular mechanisms on soybean drought tolerance. Furthermore, the two homologues of LHY1a and LHY1b provide alternative targets for genome editing to rapidly generate mutant alleles in elite soybean cultivars to enhance their drought tolerance. [ABSTRACT FROM AUTHOR]

This paper analyses extreme rainless periods for the territory of Serbia in southeast Europe. Treated as meteorological droughts from an agriculture perspective, the number of rainless periods longer than 20 days as well as their distributions is examined for the growing season (April–September) using data from a period of 50 years. The related stochastic process is modelled via the Zelenhasic–Todorovic (ZT) method for 20 evenly distributed locations across Serbia and important results are mapped in a geographic information system (GIS) environment. The principal components of the process are the number of rainless periods following a Poisson distribution, the theoretical exponential distribution of all droughts' duration and the theoretical double exponential distribution of the (yearly) longest drought's duration. These components are significant for agriculture under climate change because frequent and long‐lasting periods without or with very small amounts of rainfall (e.g., 3 mm·m−2·day−1) have a negative impact on crop production and require additional agricultural measures. This study shows that rainless periods long up to 45 days can be expected every 5 years. Extremely long droughts up to 75 days can be expected every 100 years. The saturation effect, visible if the distribution functions of the longest rainless periods are analysed for different return periods (100, 50, 20, 10, 5 and 2 years) at different locations in Serbia, illustrates that droughts of longer than approximately 55 days may occur every 50 years, while shorter droughts (30–33 days) may be expected every second year. Through quantifying the spatial and temporal distribution of rainless periods across Serbia, this work demonstrates that periods without rain are at least equally important as periods with rain. As both are aspects of a unique climate variability process, they influence agriculture and other socio‐economic sectors and have major impacts on the reliability, resilience and vulnerability of production systems, industries and services. [ABSTRACT FROM AUTHOR]

Scientific findings confirm that Small Island Developing States (SIDS) in the Caribbean are experiencing droughts and sea level rises that are contributing to saline intrusion of underground aquifers and surface water sources. This paper, using Trinidad as a case study, analyses water governance challenges in meeting Sustainable Development Goal (SDG) 6, which addresses the sustainability of water resources. Interviews were conducted with professionals from multi‐disciplinary backgrounds. Also, data provided by the water agency were analysed to evaluate water governance practices. The main contribution of this paper is the generation of a blend of policies, good practices and tools to confront growing threats to water security and to attain sustainable development in Caribbean SIDS in an era of climate change and increasing non‐climatic stressors. The paper concludes that economic, environmental and human resources, reformed administrative and legislative systems, and technological tools are fundamental to achieving good water governance. Moreover, an array of complementary policies and technologies is needed to resolve water governance issues. However, political will to implement sustainable water resources management is the greatest challenge in attaining SDG 6. [ABSTRACT FROM AUTHOR]

Long‐term droughts, closely linked to oceanic climate variability, are a great threat to the global economy, as well as food and water security. Skillful predictions will provide enormous benefit to the human societies. By taking advantages of the newly available decadal hindcasts and target experiments from the Coupled Model Intercomparison Project phase 6 (CMIP6), this paper evaluates potential predictability and decadal prediction skill of droughts over major river basins across the globe. The results show that the CMIP6 drought prediction is skillful within 3–6 years, and the skill score is 11% higher than CMIP5 over 47% river basins. Prediction skill is enhanced by 15% (16%) over 47% (49%) basins, forced by the actual sea surface temperature over tropical eastern Pacific (North Atlantic). Our findings imply the possibility of drought adaptation based on skillful decadal prediction with sufficient lead time. Plain Language Summary: A reliable drought prediction is helpful to reduce adverse impact and economic loss by increasing the preparedness. Although operational seasonal drought prediction has been applied over the world, decadal prediction is still a grand challenge due to limited knowledge about the predictability and mechanism of long‐term drought. Here we apply the decadal hindcasts from CMIP6 to evaluate the probabilistic decadal prediction skill of drought and analyze the impacts of sea surface temperature on the prediction through CMIP6 pacemaker experiments. Our results show the skillful prediction can be found over half of the major river basins at 1–4 years lead. In addition, incorporating the actual sea surface temperature in tropical eastern Pacific or North Atlantic can efficiently enhance the drought prediction skill over 48% basins as well. This study suggests that it is possible to provide useful long‐term drought information for water and agricultural management through using coupled models, but the skill can be improved further by optimization of initialization and ensemble methods. Key Points: Probabilistic predictions of basin‐scale droughts by dynamical models are skillful within 3–6 years across the globeThere is an 11% improvement from CMIP6 models compared to CMIP5 over 47% of the largest 177 global river basinsSSTs in the tropical eastern Pacific and the North Atlantic have critical importance for the success over about 48% basins [ABSTRACT FROM AUTHOR]

Future precipitation changes impact the availability of water resources and related flood and drought events. Recent studies have focused on the variations in precipitation based on the Representative Concentration Pathways scenarios, which do not reflect the current mitigation commitments of the Paris Agreement to stabilize the global mean temperature below the 2.0°C threshold. This paper analyzes the Asian precipitation response to emissions scenarios from warming. This response is a result of the Intended Nationally Determined Contributions (INDC) pledges (as of August 2018), which would satisfy the Paris Agreement target over the next few decades. Our results demonstrate that by the end of 21st century, mean precipitation in Asia will increase by 12.9% (11.7–14.7%) for a delayed action (No‐policy) scenario, 8.0% (6.7–8.8%) for a continued mitigation action (continued INDC‐pledge) scenario, and 2.4% (1.9–3.5%) and 4.4% (3.7–5.4%) for scenarios that stabilize the global mean temperature at the 1.5 and 2.0°C levels, respectively. The spatial heterogeneity of precipitation changes, however, reflects the complexity of precipitation responses in future climate projections. Furthermore, heavy rainfall events will become stronger as warming increases; however, the trend of dry spell events varies depending on the region. Considering the impacts of precipitation‐related extremes, we determined that the projected population exposure to heavy rainfall and dry spell events will significantly increase in most Asian regions. Limiting warming to lower levels (such as 1.5 or 2.0°C) would reduce the population exposure to heavy rainfall, thereby avoiding impacts associated with precipitation extremes. These results contribute to an improved understanding of the risks related to future climate extremes. Such information is crucial for planning mitigation and adaptation activities in Asia, which is home to nearly 60% of the global population. [ABSTRACT FROM AUTHOR]

Our paper reviews recent progress in the study and understanding of observed trends in extreme rainfall events in the Metropolitan Area of São Paulo (MASP). These are discussed in relation to hydrometeorological hazards that trigger natural disasters, such as flash floods, landslides, and droughts, that affect the population and local economies. A review of the most updated literature on rainfall and extremes in the MASP shows a significant increase in the total volume of rainy-season rainfall during the last seven decades. While there were practically no days with heavy rain (more than 50 mm) in the 1950s, these days have been occurring two to five times a year in the last 10 years. This, together with the inappropriate occupation of risky areas, such as slopes and banks of watercourses, leads to inundation, flooding, and landslides. Changes in extremes can be partly due to natural climate variability but can also be related to global warming and/or urbanization. There is ample evidence of an increasing risk of rainfall-related hazards in theMASP. This is particularly so for landslides in vulnerable areas. Exposure will continue to lead to risk increases. This calls for significant improvement in climate and disaster risk reduction and management efforts in theMASP region. [ABSTRACT FROM AUTHOR]

Nonstructural carbohydrates (NSCs) facilitate the adaptation of trees to drought stress. There have been a large number of studies exploring NSC changes in individual plant species and individual organ under drought and showed different trends; however, an understanding of the universal pattern of the plant NSCs responses to drought, particularly to drought duration, is still lacking. Here, we compiled data from 47 experimental studies on 52 tree species and conducted a meta‐analysis to evaluate the responses of soluble sugars, starch, and TNSC (total nonstructural carbohydrates including both soluble sugars and starch) concentrations in different tree organs (leaf, stem, and root) to drought intensity and duration. We found that starch in all organs decreased and soluble sugars in leaf increased with prolonged experiment time, and the changes in soluble sugars in all organs were stronger under severe drought than under slight‐to‐moderate drought. Under slight‐to‐moderate drought, the NSC content of each organ varied with time, while with the extension of the drought duration, the NSCs gradually approached the control value (no drought stress); this trend remained in the late drought, which means that trees activated physiological regulation processes to increase carbon storage and reduce the risks of carbon starvation. In contrast, long‐term severe drought could lead to a net loss of carbohydrates, especially in the root, implying that prolonged severe drought could lead to NSC depletion in the whole plant. As prolonged drought duration has occurred in and is projected for many regions, this paper could shed light into studies on how trees respond and adapt extending drought duration through nonstructural carbon production, transportation, and reallocation. [ABSTRACT FROM AUTHOR]

The extreme conditions of the summer season in 2018 in England gave rise to comparisons with earlier drought events. Using the information provided by documentary records, such as chronicles, accounts and diaries, this paper investigates extreme summer droughts in the period 1200–1700, and their impacts under the conditions of natural climate variability and before the provision of modern infrastructure. [ABSTRACT FROM AUTHOR]