Severe Drought Events Research Articles

Long-term hydrological drought monitoring and trend analysis in Blue Nile River basin.

This research aims to monitor the hydrological drought trends within the geographical confines of Ethiopia, Sudan, and Egypt in the Blue Nile River Basin. Historical drought circumstances in the basin were analyzed through the utilization of the stream flow drought index (SDI). The long-term historical drought trend was investigated via the application of the Mann - Kendall Sen (MK) test. Streamflow data were collected at the border (GERD) (Ethiopia) and Khartoum and Dongola (Sudan) spanning the period from 1900 to 2001. Four distinct temporal scales were examined, including monthly (SDI1), seasonal (SDI3), bi-annual (SDI6), and annual (SDI12) frequency. Notably, SDI1, SDI3, and SDI6 exhibited a higher frequency of drought occurrences, whereas SDI12 demonstrated lower frequencies, accompanied by the longest duration of drought in all gauged stations. For the preceding 102-year period, two extreme drought events were identified across all stations: 1912/1913 and 1913/1914 in the Border and Dongola stations, and 1912/1913 and 1986/1987 in the Khartoum station. Moreover, the SDI12 results revealed that severe drought events manifested three, six, and four times, in the Border, Khartoum, and Dongola stations, respectively. Furthermore, an investigation of historical extreme and severe drought patterns led to the conclusion that extreme hydrological drought does not pose an imminent threat to downstream nations, including Egypt and Sudan. However, the trend analysis revealed that an increasing drought trend was observed in the Autumn season across all stations, while a positive trend characteristic of a wet condition was observed in the remaining seasons. Annual trend analysis did not show any statistically significant findings. Nevertheless, the study highlighted the imperative role of soil and water conservation measures in upstream countries, such as the Ethiopian highlands, in mitigating the prolonged effects of meteorological drought which gradually propagates into severe hydrological drought. Consequently, downstream nations must engage in cooperative efforts with upstream countries to address this issue collectively, rather than bestowing sole responsibility on the latter.

Spatial drought occurrences and distribution using VCI, TCI, VHI, and Google Earth Engine in Bilate River Watershed, Rift Valley of Ethiopia

Drought is a major natural hazard in Ethiopia, posing significant challenges and severe consequences. This research aimed to assess the occurrence and distribution of drought in the Bilate River Watershed (BRW) using the Vegetation Health Index (VHI), Vegetation Condition Index (VCI), and Temperature Condition Index (TCI), along with the Google Earth Engine platform. Vegetation products (MOD13Q1) and LST products (MOD11A2) were selected from May to October each year, covering the period from 2000 to 2022. The VCI, TCI, and VHI maps were generated, identifying extreme and severe drought events with extensive spatial coverage in 2002, 2009, 2015, and 2022, which were the major drought years. According to the VHI, the watershed experienced extreme, severe, and moderate drought classes in May and October, affecting 62% and 70% of the area, respectively. The years 2009 and 2015 were particularly devastating in terms of drought. . The spatial autocorrelation analysis demonstrated significant positive autocorrelation of drought, as indicated by the values of Moran’s I and z scores, which ranged from 0.23 to 0.79 and 8.66 to 24.64, respectively. The correlation analysis findings showed strong positive relationships among the vegetation indices and rainfall, while showing negative associations with temperature and land surface temperature. The frequency analysis also revealed a significant occurrence of drought in the southern portion of the watershed. Therefore, these results hold practical significance for decision-makers and practitioners involved in drought management planning within the BRW.

The Influence of North Atlantic Dipole Sea Surface Temperature Anomalies on Autumn Drought Over Southwest China

ABSTRACTIn recent decades, there has been a notable increase in the frequency and severity of drought events in Southwest China (SWC), which have significantly impacted agriculture and the social economy. Using sea surface temperature (SST) data from the Hadley Centre, daily meteorological drought composite index grid data and ERA5 reanalysis data, we investigate the characteristics of autumn drought in SWC and discuss its possible causes using empirical orthogonal function (EOF) analysis. The results indicate a distinct ‘Northeast–Southwest’ dipole pattern of autumn drought over SWC in the past decade, which we define as the ‘Chuan‐Yu’‐type drought. A British–Okhotsk Corridor (BOC) pattern Rossby wave train, presenting over Eurasia, is identified as the key factor influencing the ‘Chuan‐Yu’‐type drought in SWC during the autumn. The BOC‐pattern Rossby wave train not only obstructs water vapour transport channels in SWC but also induces anomalous descending motions in the lower to middle troposphere over the region, leading to high temperatures and insufficient precipitation. Further investigation reveals that North Atlantic dipole SST anomalies trigger the BOC‐pattern Rossby wave train in autumn. The results of the linear baroclinic model sensitivity simulations support the above conclusion. These findings will make valuable contributions to autumn drought prevention and mitigation in SWC.

Large-Scale Maize Condition Mapping to Support Agricultural Risk Management

Crop condition mapping and yield loss detection are highly relevant scientific fields due to their economic importance. Here, we report a new, robust six-category crop condition mapping methodology based on five vegetation indices (VIs) using Sentinel-2 imagery at a 10 m spatial resolution. We focused on maize, the most drought-affected crop in the Carpathian Basin, using three selected years of data (2017, 2022, and 2023). Our methodology was validated at two different spatial scales against independent reference data. At the parcel level, we used harvester-derived precision yield data from six maize parcels. The agreement between the yield category maps and those predicted from the crop condition time series by our Random Forest model was 84.56%, while the F1 score was 0.74 with a two-category yield map. Using a six-category yield map, the accuracy decreased to 48.57%, while the F1 score was 0.42. The parcel-level analysis corroborates the applicability of the method on large scales. Country-level validation was conducted for the six-category crop condition map against official county-scale census data. The proportion of areas with the best and worst crop condition categories in July explained 64% and 77% of the crop yield variability at the county level, respectively. We found that the inclusion of the year 2022 (associated with a severe drought event) was important, as it represented a strong baseline for the scaling. The study’s novelty is also supported by the inclusion of damage claims from the Hungarian Agricultural Risk Management System (ARMS). The crop condition map was compared with these claims, with further quantitative analysis confirming the method’s applicability. This method offers a cost-effective solution for assessing damage claims and can provide early yield loss estimates using only remote sensing data.

A multi‐year case study highlighting the influence of hydrological conditions on epidemic dynamics in a natural plant pathosystem

The scale of influence of hydrological and thermal conditions on disease remains uncertain for most wild plant pathosystems, thus restricting our ability to predict the impacts of climate change. Analysis of the spatiotemporal spread of a fungal rust pathogen throughout four naturally occurring flax populations over the course of five growing seasons reveals relationships between epidemic magnitude and snow cover, relative humidity and temperature, as well as an unexpectedly significant effect of severe drought on disease progression. These results indicate that climate change will likely disrupt wild plant epidemics, and points to a need for further epidemiological studies characterizing the effects of environmental conditions on population‐level disease dynamics in natural pathosystems.

Restoration treatments enhance tree growth and alter climatic constraints during extreme drought.

The frequency and severity of drought events are predicted to increase due to anthropogenic climate change, with cascading effects across forested ecosystems. Management activities such as forest thinning and prescribed burning, which are often intended to mitigate fire hazard and restore ecosystem processes, may also help promote tree resistance to drought. However, it is unclear whether these treatments remain effective during the most severe drought conditions or whether their impacts differ across environmental gradients. We used tree-ring data from a system of replicated, long-term (>20 years) experiments in the southwestern United States to evaluate the effects of forest restoration treatments (i.e., evidence-based thinning and burning) on annual growth rates (i.e., basal area increment; BAI) of ponderosa pine (Pinus ponderosa), a broadly distributed and heavily managed species in western North America. The study sites were established at the onset of the most extreme drought event in at least 1200 years and span much of the climatic niche of Rocky Mountain ponderosa pine. Across sites, tree-level BAI increased due to treatment, where trees in treated units grew 133.1% faster than trees in paired, untreated units. Likewise, trees in treated units grew an average of 85.6% faster than their pre-treatment baseline levels (1985 to ca. 2000), despite warm, dry conditions in the post-treatment period (ca. 2000-2018). Variation in the local competitive environment promoted variation in BAI, and larger trees were the fastest-growing individuals, irrespective of treatment. Tree thinning and prescribed fire altered the climatic constraints on growth, decreasing the effects of belowground moisture availability and increasing the effects of atmospheric evaporative demand over multi-year timescales. Our results illustrate that restoration treatments can enhance tree-level growth across sites spanning ponderosa pine's climatic niche, even during recent, extreme drought events. However, shifting climatic constraints, combined with predicted increases in evaporative demand in the southwestern United States, suggest that the beneficial effects of such treatments on tree growth may wane over the upcoming decades.

Characteristics of Meteorological Drought Evolution in the Yangtze River Basin

Amid global climate change, recurrent drought events pose significant challenges to regional water resource management and the sustainability of socio-economic growth. Thus, understanding drought characteristics and regional development patterns is essential for effective drought monitoring, prediction, and the creation of robust adaptation strategies. Most prior research has analyzed drought events independently in spatial and temporal dimensions, often overlooking their dynamic nature. In this study, we employ a three-dimensional methodology that accounts for spatiotemporal continuity to identify and extract meteorological drought events based on a 3-month standardized precipitation evapotranspiration index (SPEI3). Measured by the SPEI3 index, the incidence of drought increased in the middle part of the basin, especially in some parts of Sichuan and Yunnan province, and the frequency of drought events decreased in the upper reaches. We evaluate drought events within the Yangtze River basin from 1980 to 2016 by examining five variables: chronology, extent, severity, duration, and epicenter locations. The results show that a total of 97 persisting drought events lasting at least 3 months have been identified in Yangtze River basin. Most events have a duration between 4 and 7 months. The findings indicate that while the number of drought events in the Yangtze River basin has remained unchanged, the intensity, duration, and severity of these events have shown a slight increase from 1980 to 2016. The drought events gradually moved from the western and southeastern parts of the basin to the central region. The most severe drought event occurred between January 2011 and October 2011, with a duration of 10 months and an affected area of 0.94 million km2, impacting over fifty percent of the basin. Changes in wetness and dryness in the Yangtze River basin are closely related to El Niño/Southern Oscillation (ENSO) events, with a positive correlation between the intensity of cold events and the probability of extreme drought. This study enhances our understanding of the dynamics and evolution of drought events in the Yangtze River basin, providing crucial insights for better managing water resources and developing effective adaptation strategies.

Assessment and pre-assessment of compound hot and drought events over Yangtze River Basin

Abstract The severe compound hot and drought event (CHDE) in 2022 had serious impacts on water resources, agriculture, power supply, and ecosystems in the Yangtze River Basin (YRB). In this paper, we asked, have similar spatiotemporally overlapping compound events, like the one observed in 2022, occurred historically in the basin? And, if so, how can we pre-assess the impacts of such potential events on subseasonal timescales? To address these questions, regional CHDEs in the YRB since 1961 were systematically identified and comprehensively assessed using a modified intensity–area–duration technique and hazard assessment methods. Additionally, the subseasonal pre-assessment capability for CHDEs in the YRB using the China Meteorological Administration’s third-generation climate model prediction system (CPSv3-S2S) was demonstrated. A total of 140 CHDEs occurred during 1961–2022, with the 21st century showing a remarkably high risk of such events. Among these, 2022 was the most intense year, with the event from July 26th to August 30th being unprecedented in severity. CPSv3-S2S effectively forecast this event’s occurrence within a 1–25 lead days, particularly in pre-assessing its extensively impacted area and high-hazard centers in the upper and middle reaches of the main river course. This pre-assessment method serves as a valuable reference in decision-making to anticipate and mitigate the risks of hydropower supply shortages and heightened electricity demand during extremely high temperatures in upstream areas.

Fluvial Sediment Load Characteristics from the Yangtze River to the Sea During Severe Droughts

Most river deltas worldwide are located in well-developed, densely populated lowland regions that face challenges from accelerated sea level rise. Deltas with morphological equilibrium are the foundation for associated prosperous economies and societies, as well as for preserving ecological fragile environments. And for deltas to be in morphological equilibrium, sufficient fluvial sediment supplies are fundamental. Severe droughts have significant impacts on the sediment load discharged to the sea, but this is considerably less studied compared to flooding events. This study examines the characteristics of Yangtze River sediment flowing toward the East China Sea during severe droughts. The effect of the Three Gorges Dam (TGD) was investigated by comparing the difference before and after its construction in 2003. Results indicate that the sediment load from the Yangtze River to the sea has experienced a more pronounced decrease during severe drought years since 2003. The primary cause is a substantial reduction in sediment supply from the upper reaches, resulting from the impoundment of the Three Gorges Reservoir created in 2003 and the construction of additional major reservoirs in the upper reach thereafter. Simultaneously, this is accompanied by the fining of sediment grain size. The fining of sediment and considerably reduced sediment load discharged to the sea during severe droughts after 2003 are likely to accelerate the erosion of the Yangtze subaqueous delta. The rating parameter values during severe drought years fall within the range observed in normal years, indicating that these drought events do not align with extreme rating parameter values. Less than 30% of the average discrepancy between measured and reconstructed sediment loads in severe drought years before 2003, and approximately 10% of the discrepancy after 2003, demonstrate the feasibility of reconstructing sediment loads for severe drought events using a sediment rating curve. This rating curve is based on daily water discharge and sediment concentration data collected during the corresponding period. These findings indicate that the rating curve-based reconstruction of sediment load performs well during severe droughts, with relative error slightly exceeding the average error of normal years prior to 2003 and approaching that observed after 2003. This study provides insights on sediment management of the Yangtze River system, including its coastal zone, and is valuable for many other large river systems worldwide.

Drought Dynamics in Sub-Saharan Africa: Impacts and Adaptation Strategies

The escalation in both frequency and severity of drought events has significantly amplified the vulnerability of numerous countries, particularly in developing ones, imposing substantial economic, environmental, and social pressures. This article presents a systematic review of drought occurrences in Sub-Saharan Africa (SSA), examining historical trends, current impacts, and projected future implications. Through this comprehensive assessment, a clear trend of intensifying drought phenomena emerges across SSA, leading to crop failures, drying of water sources, loss of pasture, food shortages, and an increase in food prices. This review also highlights the concerning potential for worsening conditions in certain regions, resulting in consequences such as migration, food insecurity, malnutrition, family disintegration, crop losses, and increased disease prevalence, notably HIV/AIDS. This study further reveals that current adaptation measures by governments and NGOs should be improved to effectively adapt to the diverse impacts of drought, and it contributes to a deeper understanding of drought dynamics in Sub-Saharan Africa and assesses its critical impacts on food security and social well-being. It also evaluates adaptation measures across different countries, highlighting their strengths and weaknesses and enabling quick identification of areas for improvement. Additionally, it informs resilience-building efforts in vulnerable communities.

Integrating remote sensing modeling for drought assessment and vegetation monitoring in El Tarf, Algeria: a 40-year analysis

The escalating frequency and intensity of drought events, exacerbated by anthropogenic climate change, present critical challenges to hydrological resources, ecosystem resilience, and agricultural productivity. In North Africa, and specifically Algeria, comprehending the spatiotemporal patterns of drought is essential for sustainable water resource management and ecological conservation. This investigation focuses on the El Tarf region, located in northeastern Algeria, recognized for its ecological diversity and agricultural relevance. Employing a synergistic methodology, this study integrates the Standardized Precipitation Evapotranspiration Index (SPEI) for long-term drought severity evaluation with the Normalized Difference Vegetation Index (NDVI) to monitor vegetation phenology and health over time. Utilizing the computational power of Google Earth Engine, we process extensive temporal datasets of SPEI spanning from 1980 to 2023, complemented by high-resolution satellite imagery for NDVI computation. This comprehensive approach facilitates an in-depth analysis of drought dynamics, their severity, and impacts on vegetative cover in El Tarf over the past four decades. Our findings indicate significant long-term drought trends, with notable dry spells occurring between 1994 and 2003. Severe drought events were particularly pronounced in December 2022 (SPI = -2.50) and May 2002 (SPI = -2.2), correlating with substantial precipitation deficits. Although areas experiencing extreme drought have diminished, there has been an increase in moderate drought occurrences, suggesting an uptick in drought frequency, which poses risks to hydrological resources and ecosystem health. These observed patterns align with regional climate change projections, highlighting an urgent necessity for adaptive management strategies in agriculture and water resources.

A Multiscalar Standardized Vapor Pressure Deficit Index for Drought Monitoring and Impacts

ABSTRACTVapour pressure deficit (VPD) is a critical measure of the atmospheric demand for water and can be used to assess short‐term and seasonal drought. To provide for probabilistic comparisons of VPD across space and time, we develop a Standardized Vapor Pressure Deficit Index (SVPDI). Similar to the way that other standardised drought indices are used, SVPDI allows for the analysis and comparison of changes in VPD across regions with different base level VPD values. It also should be useful for analysing impacts on vegetation that has varying levels of adaptation to high VPD. We use 1‐, 3‐, 6‐ and 12‐month timescales for the development of SVPDI and show that the gamma distribution is superior to other zero‐limited probability distributions for analysing VPD and, therefore, for calculating SVPDI. Then, focusing on the short‐term variations at the 1‐ and 3‐month timescales, we show how SVPDI has changed globally from 1958 to 2023 and how those changes differ from those of the commonly used Standardized Precipitation Evaporation Index (SPEI). We find that SVPDI shows more widespread drying conditions that also are larger in magnitude compared to those of SPEI. Although the two indices are moderately well correlated across the terrestrial surface, we discover that they are more decoupled in humid and arid regions compared to dry sub‐humid and semi‐arid regions. Using four locations that have recently experienced severe drought, we find that SVPDI generally showed longer drought duration and more severe drought events in the last decade when compared to SPEI.

Environmental impacts of the billion tree Tsunami project in Khyber Pakhtunkhwa on the dynamics of Agro-Meteorological Droughts

Changes in forest cover are closely associated with the variability in meteorological and hydrological variables. Therefore, this study delves into investigating how forest cover changes impact the environment (i.e., hydro-meteorological variables, including precipitation, streamflow, relative humidity (RH), evapotranspiration (ET), and temperature) using Trend Projection (TP) methods during 1980–2019. The study is carried out in the Khyber Pakhtunkhwa (KP) province of Pakistan, which witnessed deforestation between 1980 and 2010 followed by afforestation (through billion tree tsunami project, BTTP) initiated in 2014. A new drought index, named as agro-meteorological drought index (AMDI), is developed in this study using the remotely sensed data to analyze the impact of forest cover on drought severity. The robust least square regression (RLSR) model is used to regress the normalized difference vegetation index (NDVI) with AMDI at various time scales to investigate the impact of forest cover on drought severity. The RLSR and paired t-test are used to quantify the impact of forest cover and BTTP, in particular, on the environment. Land use maps prepared for KP province over a span of the past four decades revealed significant deforestation during 1985–2005, transitioning gradually to afforestation in the past decade. Results indicated a decline in streamflow throughout different seasons with an increase in forest cover, particularly during the period of afforestation (i.e., 2015–2019). The precipitation, RH (maximum/minimum), and ET displayed an increasing trend over time, whereas a decrease trend is observed in Tmax/Tmin and streamflow at most of the stations. The trend analyses depicted a significant change before and after the BTTP. The paired t-test results revealed that BTTP has statistically significant impact on the environmental variables. Furthermore, the time series plots of AMDI at different time scales indicated that drought events were frequent and severe prior to 2003, whereas significant decrease in both the frequency and severity of drought was observed in the last decade (2010–2019). The RLSR results at pixel scales demonstrated the crucial role of forest covers in alleviating both the frequency and severity of drought events. The elasticities revealed that increase in the forest cover resulted in substantial increase/decrease in each hydro-meteorological variable. Overall, the results highlighted a positive and statistically significant impact of forest cover (i.e., BTTP) on both the environment and drought variability.

Evaluating Hydrologic Model Performance for Characterizing Streamflow Drought in the Conterminous United States

Hydrologic models are the primary tools that are used to simulate streamflow drought and assess impacts. However, there is little consensus about how to evaluate the performance of these models, especially as hydrologic modeling moves toward larger spatial domains. This paper presents a comprehensive multi-objective approach to systematically evaluating the critical features in streamflow drought simulations performed by two widely used hydrological models. The evaluation approach captures how well a model classifies observed periods of drought and non-drought, quantifies error components during periods of drought, and assesses the models’ simulations of drought severity, duration, and intensity. We apply this approach at 4662 U.S. Geological Survey streamflow gages covering a wide range of hydrologic conditions across the conterminous U.S. from 1985 to 2016 to evaluate streamflow drought using two national-scale hydrologic models: the National Water Model (NWM) and the National Hydrologic Model (NHM); therefore, a benchmark against which to evaluate additional models is provided. Using this approach, we find that generally the NWM better simulates the timing of flows during drought, while the NHM better simulates the magnitude of flows during drought. Both models performed better in wetter eastern regions than in drier western regions. Finally, each model showed increased error when simulating the most severe drought events.

Carbon sequestration in a typical mountain lake associated with earthquakes, floods, droughts, and human activities in southern Altay during the late Holocene

Lakes, being key regulators of atmospheric carbon dioxide (CO2), have not yet been intensively explored in the carbon cycle. This study provides an attempt to investigate how carbon sequestration in mountain lakes responds to seismic activities, extreme climate events and human disturbance. The new data of grain-size end members (EMs), TN contents, C/N, concentrations of algal spores, and P and Mn contents, in addition to previously published data of TOC and Ca contents, Zr/Rb, Rb/Sr, and land-pollen assemblages of a well-dated sediment core from Yileimu Lake, depicted a more detailed history of environmental evolution in the region. A great earthquake happened in southern Altay at ∼ 3500 cal yr BP that triggered extensive landslides around the lake, and then frequent floods eroded the catchment between ∼ 3500 and 2300 cal yr BP, subsequently severe drought events occurred within the period of 2300–1000 cal yr BP, finally agricultural and pastoral activities intensified within the last 1000 yrs. Organic carbon accumulation rate (OCAR) in Yileimu Lake was extremely high (an underestimated value of ∼ 370 g m–2 yr–1) during the earthquake event, in response to the rapid accumulation of landslide materials. Regional comparison revealed that summer temperature was unexpected to have determined the OCAR during both flood and drought events (average 4.07 and 3.64 g m–2 yr–1, respectively), because it dominated the production of land- and aquatic plants. Human activities increased the OCAR prominently (averages 6.26 g m–2 yr–1) via changing sediment production and vegetation planting, which decoupled the OCAR from climate factors. These data imply that carbon sequestration in lakes from mountain areas where temperature adversity stress dominated vegetation growth would have the potential to increase under anthropogenic warming. In addition, seismically induced carbon sequestration in lakes from tectonically active regions cannot be ignored.

Severe and long-lasting meteorological drought events develop from precipitation deficits of mixed continental and oceanic origin

Drought is one of the most damaging hydroclimatic hazards, impacting environmental systems and socioeconomic sectors. Therefore, understanding the physical mechanisms that cause drought events is of critical importance. Here we investigate the influence of oceanic and continental moisture deficits on global meteorological drought events in recent decades, utilizing a Lagrangian dispersion model to track the origin of precipitation deficits leading to droughts. Additionally, meteorological drought events between 1980 and 2018 were segmented based on a three-dimension algorithm considering spatial extent, duration, and magnitude of drought events. Severe meteorological drought events exhibit mixed contribution of precipitation deficits from both continental and oceanic sources. This highlights the importance of considering both types of deficits in understanding severe meteorological droughts. Comparative analysis across time periods shows a consistent pattern in the dominant mixed contribution of precipitation deficits. There is no relevant decadal change in the mixed contributions of these deficits, which implies stability in the prevalence of oceanic and continental sources driving extreme drought events. These findings offer valuable insights into the factors shaping meteorological drought evolution.

The collapse of the Ming Dynasty actually began with the Wanli megadrought: Insights from a hydroclimate reconstruction based on tree-ring δ18O over the past 460 years

Climate change has played a pivotal role in shaping Chinese history, especially during the Ming Dynasty. Previous studies have focused primarily on the Chongzhen megadrought, which is widely considered as the primary climatic perturbation behind the demise of the Ming Dynasty. However, relatively little is known about other severe drought events and their potential impact on the dynasty collapse. Additionally, the characteristics of an exceptional climatic anomaly termed the “Late Ming Weak Monsoon Period” are unclear. In this study, we reconstructed the historical variations of Palmer Drought Severity Index for July–September based on tree-ring stable oxygen isotopes (δ18O) from 1556 CE to 2015 CE in southwest Chinese Loess Plateau. Our study reveals a significant weakening of the Asian summer monsoon between 1561 CE and 1661 CE, consistent with the Late Ming Weak Monsoon Period, and unravels its structural characteristics in detail. Our reconstruction also captures a distinct humidification trend over northwest China since the early 2000s. Notably, in addition to the well-known Chongzhen megadrought, our study records the severe Wanli megdrought (1585–1590 CE) during the late Ming Dynasty, an event that rarely featured in earlier studies, exhibiting comparable duration and severity to the Chongzhen megadrought. Further analysis indicates that Wanli megadrought may have served as an early trigger for the collapse of the Ming Dynasty. Furthermore, our analysis implicates the El Niño–Southern Oscillation as a contributing factor in both the Wanli and Chongzhen megadroughts, and thus to the ultimate collapse of the Ming Dynasty by affecting the Asian summer monsoon intensity.

Droughts reshape apex predator space use and intraguild overlap.

Droughts are increasing in frequency and severity globally due to climate change, leading to changes in resource availability that may have cascading effects on animal ecology. Resource availability is a key driver of animal space use, which in turn influences interspecific interactions like intraguild competition. Understanding how climate-induced changes in resource availability influence animal space use, and how species-specific responses scale up to affect intraguild dynamics, is necessary for predicting broader community-level responses to climatic changes. Although several studies have demonstrated the ecological impacts of drought, the behavioural responses of individuals that scale up to these broader-scale effects are not well known, particularly among animals in top trophic levels like large carnivores. Furthermore, we currently lack understanding of how the impacts of climate variability on individual carnivore behaviour are linked to intraguild dynamics, in part because multi-species datasets collected at timescales relevant to climatic changes are rare. Using 11 years of GPS data from four sympatric large carnivore species in southern Africa-lions (Panthera leo), leopards (Panthera pardus), African wild dogs (Lycaon pictus) and cheetahs (Acinonyx jubatus)-spanning 4 severe drought events, we test whether drought conditions impact (1) large carnivore space use, (2) broad-scale intraguild spatial overlap and (3) fine-scale intraguild interactions. Drought conditions expanded space use across species, with carnivores increasing their monthly home range sizes by 35% (wild dogs) to 66% (leopards). Drought conditions increased the amount of spatial overlap between lions and subordinate felids (cheetahs and leopards) by up to 119%, but only lion-cheetah encounter rates were affected by these changes, declining in response to drought. Our findings reveal that drought has a clear signature on the space use of multiple sympatric large carnivore species, which can alter spatiotemporal partitioning between competing species. Our study thereby illuminates the links between environmental change, animal behaviour and intraguild dynamics. While fine-scale avoidance strategies may facilitate intraguild coexistence during periodic droughts, large carnivore conservation may require considerable expansion of protected areas or revised human-carnivore coexistence strategies to accommodate the likely long-term increased space demands of large carnivores under projected increases in drought intensity.

Fat storage and drought tolerance in a seasonally‐adapted primate: Implications for modeling the effects of animal responses to global climate change

AbstractGlobal warming is changing habitats and affecting biodiversity, and is expected to exacerbate aridification in many regions. Animals and plants in seasonally dry tropical forests often exhibit adaptations to cope with seasonal resource limitation. However, whether these adaptations will facilitate drought tolerance or increase drought vulnerability is unclear. Here, we combine long‐term individual‐based data on phenology, morphometrics, and demographics to investigate how drought impacts the food resources, health, reproduction, and behavior of a population of Verreaux's sifaka (Propithecus verreauxi), a critically endangered lemur inhabiting dry deciduous forests in Madagascar. Between December 2010 and May 2023, the population experienced 3 years of severe drought (2016, 2017, 2022). During green periods in severe drought, the availability of high‐quality sifaka foods (young leaves, fruit) was significantly reduced and fruit tree mortality increased. This reduced availability of fruit persisted in the year after a drought, despite typical rainfall. Yet surprisingly, we found no negative effects on body condition or commonly‐used metrics for reproductive success during drought years or years following a drought. Instead, sifaka exhibited significantly higher levels of subcutaneous body fat during severe droughts. We observed little change in sifaka behavior between drought and non‐drought periods. However, they were more likely to lick dew during severe drought, and spent significantly less time feeding on young and mature leaves. They also significantly increased their time feeding on flowers and fruits, despite the reduced abundance of fruit in the habitat. Together, our results suggest that increased consumption of water‐rich fruit and flowers during severe droughts could facilitate physiological mechanisms that help sifaka cope with water scarcity, including fructose‐mediated fat storage, metabolic water production, and water conservation. These results provide new insights into how critically endangered animals may respond to climate change, suggesting that behavioral and physiological adaptations to seasonal resource limitation may buffer some mammals from the effects of severe drought or other extreme weather events.

A direct comparison of the radial growth response to drought of European and Oriental beech

Climate change-related extreme drought events already have a significant impact on the productivity and mortality of Central European forests. European beech (Fagus sylvatica ssp. sylvatica), one of the most important European broadleaved species, has responded to such drought periods with increasing mortality and reduced volume increment. This has raised concerns about its suitability and adaptive capacity in relation to future climatic conditions and motivated the search for alternative tree species that are suitable for assisted migration into European beech forests. One of the candidates is the Oriental beech species complex (F. sylvatica ssp. orientalis), whose range extends from the Balkan to Iran and, at least in some parts of its range, grows under a warmer and drier climate. In order to evaluate whether Oriental beech is more drought tolerant, we compared the radial growth response to droughts between 1920 and 2018 of a total of 138 European and 122 Oriental beeches growing under identical site conditions in eight different locations in Germany and France. The species identity of all analysed trees was verified by microsatellite analyses, and the origin of the introduced Oriental beech was traced to the Greater Caucasus (7 stands) and the Black Sea coast (1 stand). The drought responses of radial growth were quantified using the indices resistance, resilience, and recovery as suggested by Lloret et al. (2011) and growth recovery time (GRT) (Thurm et al., 2016) and used as response variables in generalized linear mixed effect models.Considering only the average radial growth response to severe and extreme drought events, both the different Lloret indices and the GRT did not show prominent difference between Oriental and European beech. However, the mixed model analyses, which also included interaction terms, revealed interspecific differences in drought tolerance, depending on the intensity and timing of the drought. In extreme summer drought years, values of resistance predicted by the mixed-effect models were significantly higher in Oriental beech than in European beech, whereas its resilience was only slightly better than in European beech, regardless of drought intensities. In contrast, Oriental beech was much more susceptible to spring drought with significantly weaker growth recovery and distinctly longer growth recovery times.Based on these results, Oriental beech provenances from the Caucasus do not appear to be sufficiently more drought tolerant than European beech to justify an assisted migration approach to adapt Central European forests to climate change. To analyse the drought tolerance of Oriental beech more comprehensively, introduced trees representing other genetic clusters need to be analysed, as well as the effects of repeated drought events on growth and mortality.