The intensity and frequency of drought are increasing in the tropical zone of China under global warming, and accurate assessment of drought severity and duration is critical for sustainable ecosystem management. Previous studies usually rely on one or more drought indices calculated from meteorological station or reanalysis data. However, the assessment results based on these drought indices are not consistent, which can be due to the differences in data sources and index parameters. In this study, we aim to identify the optimal dataset and drought index, and accurately evaluate the drought severity and drought duration in the tropical zone of China. We assessed the accuracy of five drought indices, namely Precipitation Anomaly in Percentage (PA), Relative Moisture Index (MI), Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI) and Meteorological Drought Composite Index (MCI), calculated from meteorological station data and the China Meteorological Forcing Dataset (CMFD) with respect to drought records compiled by local government. Results indicate that the drought index calculated based on meteorological station data can better match the government-compiled drought records than CMFD. MI is the optimal index for drought severity and duration assessment in study area, especially for winter-spring drought and severe drought, followed by PA. The normalized bell-shaped line of fitted precipitation in winter and spring is biased towards the less rainy side in SPI calculations, which leads to more underestimation even for officially recommended MCI, and actual water supply are also misrepresented in SPEI calculations. This study offers valuable insights for policymakers to use optimal dataset and drought index to accurately assess the drought events, and take effective measures to alleviate its impact on tropical ecosystems in China.

Evaluating drought parameters at the basin level is one of the fundamental processes for planning sustainable crop production. This study aimed to evaluate both short-term and long-term meteorological drought parameters within the Vaippar Basin, located in southern India, by employing the standardized precipitation index (SPI). Gridded rainfall values developed from 13 rain gauge stations were employed to calculate the SPI values. Drought parameters, encompassing occurrence, intensity, duration, frequency, and trends, were assessed for both short-term and long-term droughts. The study findings indicated that the occurrence of short-term drought was 51.7%, while that of long-term drought was 49.82%. Notably, the basin experienced extreme short-term droughts in 1980, 1998 and 2016 and long-term droughts in 1981, 2013, and 2017. Utilizing an innovative trend identification method for SPI values, a significant monotonic upwards trend was identified in October and December for short-term drought and in December for long-term drought. This study defined the minimum threshold rainfall, which represents the critical amount required to prevent short-term drought (set at 390 mm) and long-term drought (set at 635 mm). The drought severity recurrence curves developed in this study indicate that when the SPI values fall below - 1.0, short-term drought affects 25% of the basin area, while long-term drought impacts 50% of the basin area at a 20-year recurrence interval. Additionally, the drought hazard index (DHI), which combines drought intensity and severity, demonstrated higher values in the northwestern regions for short-term drought and in the southern areas for long-term drought. The study\'s findings, highlighting areas of drought vulnerability, severity, and recurrence patterns in the basin, direct the attention for timely intervention when drought initiates.

Tree species-specific responses to drought are urgently needed for assessing the impacts of current climate change on forest ecosystems. Here, we characterized the resistance, recovery, resilience, and growth recovery periods in response to different drought events based on tree-ring width index data (>30 years) for three tree species widely distributed in northern China, among which larch (Larix principis-rupprechtii Mayr) and Mongolian pine (Pinus sylvestris L. var. mongolica Litv.) are two major species used for afforestation, and birch (Betula platyphylla Suk.) is one of the most common natural tree species. Despite no significant effects of mild drought on tree growth, severe drought events significantly reduced the growth of all species, with contrasting species-specific responses. Larch trees had the lowest resistance and resilience among the three species, and Mongolian pine trees were more resistant but had a longer recovery period than birch trees. The drought responses varied with tree size. Large Mongolian pine and birch trees were more resistant but large larch trees were much more vulnerable than small trees during severe droughts. Smaller birch trees had higher resilience to severe droughts. Our study shows species-specific differences in drought responses and suggests that drought responses are tree-size dependent and drought-intensity associated, which further provides a guidance for selecting optimal cultivated tree species and designing forest managements in this region.

Corridors with good-quality habitats maintain the spatial dynamics of metapopulations by promoting dispersal between habitat patches, potentially buffering populations, and communities against continued global change. However, this function is threatened by habitats becoming increasingly fragmented, and habitat matrices becoming increasingly inhospitable, potentially reducing the resilience and persistence of populations. Yet, we lack a clear understanding of how reduced corridor quality interacts with rates of environmental change to destabilize populations. Using laboratory microcosms containing metapopulations of the Collembola Folsomia candida, we investigate the impact of corridor quality on metapopulation persistence under a range of simulated droughts, a key stressor for this species. We manipulated both drought severity and the number of patches affected by drought across landscapes connected by either good- or poor-quality corridors. We measured the time of metapopulation extinction, the maximum rate of metapopulation decline, and the variability of abundance among patches as criteria to evaluate the persistence ability of metapopulations. We show that while drought severity negatively influenced the time of metapopulation extinction and the increase in drought patches caused metapopulation decline, these results were mitigated by good-quality corridors, which increased metapopulation persistence time and decreased both how fast metapopulations declined and the interpatch variability in abundances. Our results suggest that enhancing corridor quality can increase the persistence of metapopulations, increasing the time available for conservation actions to take effect, and/or for species to adapt or move in the face of continued stress. Given that fragmentation increases the isolation of habitats, improving the quality of habitat corridors may provide a useful strategy to enhance the resistance of spatially structured populations.

Drought is increasingly affecting farmers in agro-pastoralist and pastoralists region. It is one of the most harmful natural disasters that significantly affects rain-fed agriculture in developing countries. Drought assessment is an important component of drought risk management. This study used CHIRPS rainfall data to monitor the characteristics of drought in Borena Zone in southern Ethiopia. The standardized precipitation index (SPI) is used to calculate the magnitude, intensity, and severity of drought during the rainy season. Results show that severe and extreme droughts were detected in the first rainy season (March to May) and second wet season (September to November). Severe and extreme droughts were detected in the first rainy/wet season in 1992, 1994, 1999, 2000, 2002-2004, 2008,2009, 2011, 2019-2021. The spatial and temporal variability of drought is highly influenced by El Nino-Southern Oscillation (ENSO) in Ethiopia. Results revealed that most of the first rainy season was dry. 2011 was the driest year during the first wet season. Drought risk events in the first wet season were greater than in the second wet season. Results show that drought more frequently occurred in the northern and southern part in the first wet season. In the second rainy season extreme drought was detected in 1990, 1992, 1993, 1994, 1996, and 1997. The results of this study will promote the importance of early warning measures, drought risk management, and food security management in the study area.

In Poland, recent summer droughts have had devastating environmental, social, and economic consequences, but the trend of growing season dryness remains unclear. This study focuses on the soil moisture and evaporative stress conditions, analyzed in a multiyear period between 1981 and 2019. Country scale trends in growing season drought severities are assessed using indices derived from the model-based estimates of soil moisture and evapotranspiration. These are compared with indices derived from meteorological variables. Soil droughts are assessed by the Standardized Soil Index (SSI), while the ecological droughts are related to evapotranspiration by the Standardized Evaporative Stress Ratio (SESR). Moreover, the Standardized Precipitation Index (SPI), Standardized Precipitation Evapotranspiration Index (SPEI), and self-calibrating Palmer Drought Severity Index (sc-PDSI) are used for comparison. A Drought-Prone Area (DPA) is delineated based on a criterion defined as simultaneous occurrence of statistically significant drying trends in surface and root zone soil moisture and evaporative stress. It was found that soil and ecological drought severities have remarkably increased in the growing season. This confirms the hypothesis that intensified soil drying is accompanied by intensified water stress imprinted in evapotranspiration. The most severe drought sequence has occurred in recent years, amplified by exceptionally high air temperature, low precipitation, and high deficit in the climatic water balance. The highest correlation is observed between annual growing season drought severities derived from the SSI and SESR; only SPEI approximates an increasing trend, while the SPI and sc-PDSI do not follow such a trajectory. The study shows an almost contiguous spatial pattern of DPA, which takes 42% of the country. One important implication of this study is that soil moisture and evapotranspiration should be considered in assessing drought severity in addition to traditionally used meteorological variables.

Drought is a natural hazard that can inflict significant damage to agriculture, society, economy, and ecosystems. The assessment of the persistence of drought severity (PDS) assists in understanding the characteristics of droughts better and enables the development of associated prediction tools and models. This work explores the persistence and spatial-temporal variability of drought severity (DS) in the diverse dryland of Iran. Using monthly precipitation and temperature data of 44 synoptic stations from 1989 to 2018, relationships between DS coefficient of precipitation variation, aridity, and the persistence percentage are determined by the application of the standardized precipitation index (SPI), the dryland index, and the Hurst exponent (H). The results confirm the persistence of droughts in Iran as H exceeded the 0.5 threshold for all stations. The PDS average in Iran is 0.78 with high regional variability reflective of different climatic conditions and geographical locations. An inverse relationship exists between the long-term coefficient of variation of monthly precipitation and PDS in the hyper-arid and arid regions of watersheds. Higher PDS values and increasing trend in the DS are detected in dry-subhumid areas. Also, the effect of the El Niño-Southern Oscillation (ENSO), a teleconnection metric, on the DS displays high spatial and temporal variability in Iran. The results show that the PDS is consistent with the spatial variation of DS changes during the period of 2009-2018.

Across the Upper Missouri River Basin, the recent drought of 2000 to 2010, known as the \"turn-of-the-century drought,\" was likely more severe than any in the instrumental record including the Dust Bowl drought. However, until now, adequate proxy records needed to better understand this event with regard to long-term variability have been lacking. Here we examine 1,200 y of streamflow from a network of 17 new tree-ring-based reconstructions for gages across the upper Missouri basin and an independent reconstruction of warm-season regional temperature in order to place the recent drought in a long-term climate context. We find that temperature has increasingly influenced the severity of drought events by decreasing runoff efficiency in the basin since the late 20th century (1980s) onward. The occurrence of extreme heat, higher evapotranspiration, and associated low-flow conditions across the basin has increased substantially over the 20th and 21st centuries, and recent warming aligns with increasing drought severities that rival or exceed any estimated over the last 12 centuries. Future warming is anticipated to cause increasingly severe droughts by enhancing water deficits that could prove challenging for water management.

Increased frequency and severity of drought, as a result of climate change, is expected to drive critical changes in plant-insect interactions that may elevate rates of tree mortality. The mechanisms that link water stress in plants to insect performance are not well understood. Here, we build on previous reviews and develop a framework that incorporates the severity and longevity of drought and captures the plant physiological adjustments that follow moderate and severe drought. Using this framework, we investigate in greater depth how insect performance responds to increasing drought severity for: (i) different feeding guilds; (ii) flush feeders and senescence feeders; (iii) specialist and generalist insect herbivores; and (iv) temperate versus tropical forest communities. We outline how intermittent and moderate drought can result in increases of carbon-based and nitrogen-based chemical defences, whereas long and severe drought events can result in decreases in plant secondary defence compounds. We predict that different herbivore feeding guilds will show different but predictable responses to drought events, with most feeding guilds being negatively affected by water stress, with the exception of wood borers and bark beetles during severe drought and sap-sucking insects and leaf miners during moderate and intermittent drought. Time of feeding and host specificity are important considerations. Some insects, regardless of feeding guild, prefer to feed on younger tissues from leaf flush, whereas others are adapted to feed on senescing tissues of severely stressed trees. We argue that moderate water stress could benefit specialist insect herbivores, while generalists might prefer severe drought conditions. Current evidence suggests that insect outbreaks are shorter and more spatially restricted in tropical than in temperate forests. We suggest that future research on the impact of drought on insect communities should include (i) assessing how drought-induced changes in various plant traits, such as secondary compound concentrations and leaf water potential, affect herbivores; (ii) food web implications for other insects and those that feed on them; and (iii) interactions between the effects on insects of increasing drought and other forms of environmental change including rising temperatures and CO2 levels. There is a need for larger, temperate and tropical forest-scale drought experiments to look at herbivorous insect responses and their role in tree death.

Droughts are some of the worst natural disasters that bring significant water shortages, economic losses, and adverse social consequences. Gravity Recovery and Climate Experiment (GRACE) satellite data are widely used to characterize and evaluate droughts. In this work, we evaluate drought situations in the Yangtze River Basin (YRB) using the GRACE Texas Center for Space Research (CSR) mascon (mass concentration) data from 2003 to 2015. Drought events are identified by water storage deficits (WSDs) derived from GRACE data, while the drought severity evaluation is based on the water storage deficit index (WSDI), standardized WSD time series, and total water storage deficit (TWSD). The WSDI is subsequently compared with the Palmer drought severity index (PDSI), standardized precipitation index (SPI), standardized precipitation evapotranspiration index (SPEI), and standardized runoff index (SRI). The results indicate the YRB experienced increased wetness during the study period, with WSD values increasing at a rate of 5.20mm/year. Eight drought events are identified, and three major droughts occurred in 2004, 2006, and 2011, with WSDIs of -2.05, -2.38, and -1.30 and TWSDs of -620.96mm, -616.81mm, and -192.44mm, respectively. Our findings suggest that GRACE CSR mascon data can be used effectively to assess drought features in the YRB and that the WSDI facilitates robust and reliable characterization of droughts over large-scale areas.