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The timely and effective early warning of sudden drought events is of great importance for reducing disaster losses and drought risk. Satellite microwave remote sensing with the advanced microwave scanning radiometer (AMSR) has enabled the global monitoring of multiple components of water, such as soil moisture (SM), vapour pressure deficit (VPD), and open water fraction (OWF), on a daily scale since 2002. In this study, the applicability of the AMSR surface wetness index (ASWI) and drought features in Central Asia were studied from 2002 to 2017 based on AMSR data. This study concluded that (1) the spatial and temporal differences in the various water components and coefficient of variation of the Central Asia land–atmosphere interface were large, which led to large spatial and temporal differences under both dry and wet conditions in Central Asia; (2) although the ASWI was not significantly correlated with other drought indices (i.e., gravity recovery and climate experiment (GRACE) combined climatological deviation index (CCDI) and GRACE drought severity index (DSI)) over Central Asia, the maximum Pearson correlation coefficient (CC) between the ASWI and Palmer drought severity index (PDSI) in the Irtysh River Basin was 0.824 (p < 0.05), corresponding to a moving average window of 11 months. The CCs of ASWI and Standardized Precipitation Evapotranspiration Index on a 6‐month scale (SPEI‐6) in Central Asia were generally more than 0.8 (p < 0.05), indicating that the ASWI was effective for retrieving drought conditions in Central Asia. In addition, these four drought indices (ASWI, PDSI, GRACE‐DSI, and GRACE‐CCDI) revealed that drought occurred continuously after 2003 in Central Asia; (3) the spatial and temporal distribution of dry and wet conditions in Central Asia is closely related to the teleconnection indices (i.e., MEI, SOI, and PDO). Thus, AMSR data are critical for understanding drought events and their evolution in regions influenced by climate change. [ABSTRACT FROM AUTHOR]

Because drought is a very common and widespread natural disaster, it has attracted a great deal of academic interest. Based on 12-month time scale standardized precipitation indices (SPI12) calculated from precipitation data recorded between 1960 and 2015 at 22 weather stations in the Tarim River Basin (TRB), this study aims to identify the trends of SPI and drought duration, severity, and frequency at various quantiles and to perform cluster analysis of drought events in the TRB. The results indicated that (1) both precipitation and temperature at most stations in the TRB exhibited significant positive trends during 1960-2015; (2) multiple scales of SPIs changed significantly around 1986; (3) based on quantile regression analysis of temporal drought changes, the positive SPI slopes indicated less severe and less frequent droughts at lower quantiles, but clear variation was detected in the drought frequency; and (4) significantly different trends were found in drought frequency probably between severe droughts and drought frequency. [ABSTRACT FROM AUTHOR]

Under climate change, droughts are causing increasingly larger damages around the world, attracting the attention of governments and researchers. In this study, the terrestrial water storage anomalies (TWSA) obtained from a Gravity Recovery and Climate Experiment (GRACE) were coupled with precipitation, creating a Combined Climatological Deviation Index (CCDI). This index was used to analyze the drought events that occurred in the major basins of Central Asia between April 2002–June 2017. The main conclusions are as follows: (1) the certain but not significant (i.e., p >.05) impacts of precipitation were detected on the total water storage anomalies (TWSA) of three basins (i.e., Irtysh River Basin (IRB), Syr Darya Basin (SDB), and Amu Darya Basin (ADB)) that originate from the Tienshan Mountains based on the correlation coefficient between precipitation and terrestrial water storage (TWS); (2) the Drought Severity Index (DSI), the Palmer Drought Severity Index (PDSI), and the Standardized Precipitation Index over a 12-month scale (SPI12) were related to the CCDI in the major basins of Central Asia, suggesting that the CCDI can be applied effectively to assess the drought characteristics of these basins; (3) the most severe drought events detected by the CCDI in the IRB, SDB, and ADB occurred in 2012, 2014, and 2014, respectively. A humidification trend was observed for the IRB, while a drought trend was observed in the SDB and ADB. Therefore, it appears that the CCDI can be effectively applied to determine the severity of droughts, increase water-saving awareness, and avoid the effects of droughts. • Precipitation has little effect on TWS in Central Asia. • CCDI can character the drought events in Central Asia well. • The drought severity from CCDI was more severe than that from other traditional drought indices. • All the drought indices were discovered the obvious drought events in Central Asia during 2008–2009. [ABSTRACT FROM AUTHOR]

Propagation from meteorological to hydrological drought events is crucial for understanding drought variation mechanisms and their consequences. Most previous studies were implemented using various standardized drought indices at month scale, which were difficult to reveal the physical processes and insufficient to characterize the comprehensive propagation characteristics (e.g., propagation time, duration, and severity) from meteorological to hydrological drought events. Furthermore, the impact mechanisms of underlying surfaces on drought propagation remained unclear. This study identified the paired relationships between meteorological and hydrological drought events and investigated their comprehensive propagation characteristics at the hydrologic response unit scale using the Soil and Water Assessment Tool (SWAT), run theory and paired analysis. The impact of underlying surfaces (e.g., land use, soil type, and slope) on drought propagation was further assessed using the Student's t -test at the 95% confident level. The upper middle Yuanjiang River Basin in China, which is prone to drought and exhibits diverse underlying surface conditions, was selected as the study area. Results indicate that the SWAT model optimally simulates the monthly streamflow with the Nash-Sutcliffe efficiency being ≥0.75 and the RMSE-observations standard deviation ratio being ≤0.50. Four main propagation types are identified, i.e., one-to-one, many-to-one, one-to-many, and many-to-many, in which the first two types are the dominant ones, accounting for 86.7% and 13.3% of total paired events, respectively. More than 85% of the study area exhibits a propagation time of ≤2 months, especially in the headwater area and the right bank of Lvzhijiang River. Drought duration and severity are amplified during the propagation process in 60.8% and 60.3% of the study area, respectively. Drought propagation time, duration, and severity are mainly controlled by soil and slope, and are slightly affected by land use type. The propagation time is quite short in areas with a high soil infiltration rate and steep slope, and the drought duration and severity are amplified in areas with a low soil infiltration rate and gentle slope. This study aims to provide deep insights on propagation from meteorological to hydrological drought considering various underlying surfaces, and further provides a scientific basis for the drought propagation mechanism and for drought disaster prevention and adaptation. • Drought propagation is analysed on time, duration, and severity by paired events. • Only 55% of meteorological drought events trigger hydrological drought events. • Areas with lower soil infiltration rates and gentler slopes show shorter duration and higher severity. • Drought propagation is impacted evidently by soil, followed by slope and land use. [ABSTRACT FROM AUTHOR]

• The abrupt change of precipitation and runoff in the upper reaches of Aksu River Basin is not synchronous. • CLM-DTVGM can simulate the hydrological process of rivers in arid area of Northwest China well. • The longer the SRI time scale is, the more obvious their drought characteristics are. • Human activities have aggravated the hydrological drought in the arid area of Northwest China. Under climate change, drought events have a great impact on different regions of the world. Quantitative evaluation of regional drought characteristics is of great significance for regional drought risk aversion. This study simulates the changes in the historical and future hydrological runoff based on historical observation data, the Community Land Model-Distributed Time Variant Gain Model (CLM-DTVGM), and CMIP5 data. Subsequently, it reveals the historical and future hydrological drought characteristics in the Aksu River Basin under a changing environment. The conclusions are as follows: (1) although both the asynchronous mutated precipitation and runoff in the upper reaches of the Aksu River Basin increased, with a maximum increase of 3.3 mm and 1.2 m3/s, the synchronous mutation of precipitation and runoff in the downstream indicated that human activities only affected the runoff in Alaer station; (2) CLM-DTGVM could be well applied in historical and future runoff simulation of the Aksu River basin with complex transformation of different land use under the changing environment; and (3) the seasons of drought development, maximum intensity, and drought termination mainly occurred in winter, followed by spring, summer, and autumn, while human activities had an obvious impact on the drought characteristics in the Aksu River Basin. These findings are of great significance for improving water-saving awareness and warning against drought risk. [ABSTRACT FROM AUTHOR]

Under global warming, drought problems have become increasingly prominent, which has seriously affected the ecological environment's protection and social and economic development at global and regional scales. Ningxia is an arid region in northwest China with serious water problems, and droughts further exacerbate its water security and hinder ecological and socio-economic development. Therefore, this study explored the temporal and spatial distribution characteristics of meteorological and agricultural droughts and their driving factors in Ningxia during 2002–2021 by combining wavelet analysis and grey relational analysis. The main conclusions are as follows: (1) precipitation, soil moisture (SM), and evapotranspiration (ET) in Ningxia increased significantly, while the main meteorological drought events in Ningxia appeared around 2006, 2011, and 2015, and the agricultural drought first became stronger and then weaker; (2) precipitation and ET were correlated with meteorological drought in Ningxia, with a coefficient above 0.8, while the correlation between agricultural drought and precipitation, ET, and gross primary production (GPP) were very significant; and (3) precipitation, ET, and GPP were not all included in the drivers of meteorological drought in Ningxia, whereas agricultural drought had a grey correlation with precipitation, ET, and GPP according to the grey relational analysis. This study is of great significance for revealing the spatiotemporal characteristics and driving factors of drought in Ningxia as well as the early warning and risk management. • Ningxia experienced a state of becoming dry before becoming wet. • The correlation between agricultural drought and meteorological drought in Ningxia is not significant. • Almost all eco-hydrological factors in Ningxia have a large impact on agricultural drought. • Different ecohydrological factors have different impacts on different regions of Ningxia. [ABSTRACT FROM AUTHOR]

• The drought events in Central Asia retrieved by ASWI are consistent with the records of actual situation. • The drought centroid of Central Asia hardly occurs in the southeast. • Central Asia has experienced drought in the past two decades, followed by gradual wetting. • The water vapor flux, precipitation, and temperature have obvious influence on the occurrence of drought in Central Asia. Under warm climates, the more complex and malleable relationship between water and heat and the changes in the water components at the land–atmosphere interface pose greater challenges to understanding hydro-meteorological processes. However, the emergence of the advanced microwave scanning radiometer (AMSR) has facilitated the precise monitoring of these changes. Therefore, this study investigated and analyzed the spatiotemporal transformation characteristics of drought–wetness and its driving mechanisms in Central Asia from July 2002 to December 2018 based on the AMSR surface wetness index (ASWI) coupled with multiple water components. Three major conclusions were drawn from this investigation. First, the spatiotemporal differences in multiple water components in Central Asia caused substantial spatiotemporal differences in the extent of changes in drought–wetness. For example, arid areas were mainly concentrated in the lower reaches of the Amu Darya and Syr Darya river basins, where the dominant drought periods were 2007 and 2018. Second, the centroids of the largest drought patches were mainly located in the northeast, northwest, and southwest regions of Central Asia. Central Asia experienced a continuous drought from 2002 to 2005, and then a gradual wetting from 2008 to 2017. Third, the drought–wetness variation can be attributed to the variation of water vapor flux in the typical barometric layer as well as the variation of precipitation and temperature. The ASWI may play an essential role in drought monitoring and tracking prediction, particularly for drought risk mitigation and aversion. [ABSTRACT FROM AUTHOR]

Global precipitation has undergone significant changes due to climate change, resulting in extreme drought and flood events and remarkable losses of life and property. Therefore, based on precipitation and temperature data for the Yangtze River Basin (YRB), as well as teleconnection indices (i.e., Nino3.4, North Pacific Index [NPI], Southern Oscillation Indices [SOI], and Pacific Decadal Oscillation [PDO]), the causal relationship between the teleconnection indices and the dry/wet changes was analyzed and explored using the standardized precipitation index (SPI) and standardized precipitation evapotranspiration index (SPEI) from 1961 to 2018. Based on the findings, precipitation significantly increased in the upper and lower reaches of the YRB, with a maximum increase of 8 mm/a, and decreased in the middle reaches, with a maximum decrease of 4 mm/a. Further, the temperature in the entire YRB increased, with a maximum increase of 0.04 °C/a. The drought characteristics derived from SPI in the YRB were more uniform in spatial distribution from 1961 to 2018, with small local differences and the largest proportion of mild droughts in different drought classes; however, for those from SPEI in the YRB, local differences in spatial distribution and the largest proportion of moderate droughts in different drought classes were found. Finally, both linear and nonlinear causality between the teleconnection indices and the wet/dry changes in the YRB were significant to some extent, especially for NAO, Nino 3.4, and PDO. These causalities between the wet/dry changes and the teleconnection indices were also more significant for short periods. Related studies are important for assessing the driving forces of dry–wet changes in the YRB. • The causal relationships between dry/wet changes and teleconnection indices in the Yangtze River basin were significant; • The drought characteristics reflected by SPI and SPEI in the Yangtze River basin differed greatly; • The optimal lagged time between teleconnection indices and dry/wet changes were mainly at 1–12 months; • Different teleconnection indices have different effects on dry/wet changes in the Yangtze River basin. [ABSTRACT FROM AUTHOR]