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Meteorological drought commonly originates from precipitation deficit and is then propagated to agricultural and hydrological droughts. Since drought impacts are more directly related to agricultural and hydrological systems of human society, it is important to understand the drought propagation process for reducing drought impacts. This study investigated the propagation of meteorological droughts through the hydrological system in South Korea. We performed comparative analyses between a meteorological drought indicator [Standardized Precipitation Index (SPI) at various timescales] and a hydrological drought indicator [Palmer Hydrological Drought Index (PHDI)], and pooled the mutually dependent drought events from the indicators. The results indicated that most hydrological droughts occurred following meteorological droughts, and drought events became fewer and longer when moving from 3- and 6-month SPI to PHDI. In addition, when we investigated the meteorological conditions, about 70 - 80% of 3- and 6-month SPI corresponding to the onset of hydrological drought (PHDI = -2) were less than -1.0. We also calculated the propagation probability using the conditional probability theory with 33% (3-month SPI) and 48% (6-month SPI) of meteorological droughts propagated to hydrological drought. We concluded that even though the frequency of hydrological drought in South Korea was less than that of meteorological drought, the severity of hydrological drought was greater than that of meteorological drought. [ABSTRACT FROM AUTHOR]

The Lancang-Mekong River Basin (LMRB) has been particularly vulnerable to serious and successive droughts during the last decades. Nevertheless, the characteristics of spatiotemporal variations in meteorological drought (MD) and hydrological drought (HD) with an emphasis on drought propagation have yet to be thoroughly investigated. In this study, based on reanalysis data, the standardized precipitation index (SPI) and standardized runoff index (SRI) were employed to comprehensively examine the evolution and propagation characteristics of MD and HD. Spearman rank correlation and wavelet analyses were employed for the correlation and propagation of MD to HD. The influencing factors of the drought propagation time (DPT) were also explored. The results indicate that: (1) During 1950–2021, the regions with worsening drought conditions were primarily in the Lancang River Basin in Yunnan Province, the highlands in north Laos, and the Khorat Plateau in Thailand. (2) The drought characteristics varied significantly on different timescales. For the longer timescales, the MDs and HDs corresponded to fewer drought events but longer durations and larger severities. The average duration and severity of HD were higher than MD on all selected timescales. (3) The DPTs from MD to HD exhibited noticeable spatial variability ranging from 2 to 9 months. In addition, there were statistically positive correlations between the MD and HD in each sub-region. (4) Precipitation was the dominant factor influencing the spatial distribution of DPTs at the basin scale, while the catchment properties, represented by the land use and elevation, had non-negligible influences on the DPTs. (5) Human activities weakened the correlations between MD and HD. Meanwhile, the DPTs were prolonged as a result of human influence. Our findings highlight the characteristics of HD response to MD in the diverse sub-regions of the LMRB and provide crucial information for early warning and improvement of drought resilience in this transboundary international river. • The duration and severity of the MD prolonged and aggravated in the HD. • The DPTs exhibited noticeable spatial variability and varied from 2 to 9 months. • The spatial patterns of DPT were closely linked with climate and catchment properties. • The linkages between MD and HD have been diminished by human activities. [ABSTRACT FROM AUTHOR]

• Nonlinear Dynamic System (NDS) in phase domain is applied in drought propagation. • Nonlinear information about drought propagation can be detected by NDS. • The propagation time and rate between two types of drought can be calculated by NDS. Current approaches for calculating propagation time and rate from meteorological to hydrological drought mainly focus on the time series of SPI and SRI, and most of these methods are conducted in time domain (e.g., correlation analysis) and frequency domain (e.g., wavelet analysis), which are regarded as linear statistic methods. Inaccuracy could emerge when the complexity and nonlinearity of drought propagation is addressed by such linear methods. In light of this problem, this research adopts Nonlinear Dynamic System (NDS) conducted in phase domain, which provides a nonlinear and systematic perspective on drought propagation. NDS may conditionally generate chaos (commonly known as "butterfly" phenomenon), which was not covered by previous studies on drought propagation. Assuming an underlying NDS for drought events, we demonstrate the NDS of drought propagation could generate chaos, and the nonlinear information about the propagation from meteorological to hydrological droughts can be detected within such chaotic NDS. The propagation time of 1–5 months and the propagation rate of 0.686 were found in the Pearl River Basin. In addition, the propagation time of 3, 7 and 11 months was also found in the Wei River Basin, to prove the broad applicability of our method. The results for these two basins are verified by previous studies. [ABSTRACT FROM AUTHOR]

• A socioeconomic drought matching rule integrated with tolerance mechanism is proposed. • The thresholds for future propagation of meteorological and hydrological droughts to socioeconomic drought of different severities are calculated. • Radiative forcing boosts meteorological effect on socioeconomic drought, raising propagation threshold. The propagation threshold between different droughts is necessary to investigate the mechanism of drought evolution. At the same time, Dongjiang basin is of great significance in water resource management and regional socioeconomic development, as it is one of the main water sources in South China. However, studies have often been limited to propagation between meteorological and hydrological droughts, while studies on the propagation threshold from meteorological and hydrological droughts to socioeconomic drought have rarely been reported. This study developed a framework for the propagation threshold from meteorological and hydrological droughts to socioeconomic drought. The framework improved the method of pooling and exclusion of droughts and proposed new matching rules for different droughts. Using these rules, meteorological, hydrological, and socioeconomic drought events were consistently matched one by one. From the matched combinations of multi-type drought events using copula conditional probabilities, the propagation thresholds from meteorological and hydrological droughts to socioeconomic drought was found. The CMIP6 datasets were applied to build SPI (standardized precipitation index) and SRI (standardized runoff index) for identifying meteorological and hydrological droughts. Socioeconomic droughts based on SWSDI (standardized water supply and demand index) were further evaluated by the SWAT (Soil and Water Assessment Tool) and SD (Supply and Demand) models. Results showed that the integration of the improved pooling and exclusion method and new matching rules would provide accurate and reliable matching among meteorological, hydrological, and socioeconomic drought events in the future. The higher the severity of socioeconomic drought, the larger the propagation threshold of meteorological and hydrological droughts. The threshold for propagation from meteorological to socioeconomic drought was larger than that for propagation from hydrological to socioeconomic drought. In particular, radiation forcing significantly increased the propagation threshold between meteorological or hydrological and socioeconomic droughts. The framework provides a foundation for drought propagation and even socioeconomic drought prediction. [ABSTRACT FROM AUTHOR]

• Human activities reduced the event of SSI-1 in midstream and downstream regions. • The center of gravity method performs best in detecting the drought propagation. • Human activities have a greater impact on the drought during nongrowing season. Quantifying the role of human activities in the process of drought propagation from meteorological drought to hydrological drought is helpful in developing mitigation strategies and in prediction of hydrological drought. To quantify the role of human activities, we compared the results from using simulated natural and observed streamflow to calculate drought indices and drought propagation time. In addition, we compared different propagation detection methods for evaluating the spatiotemporal characteristics of drought propagation from meteorological to hydrological in the Yellow River Basin during the period 1962–2018. The results show: (1) The intensity of meteorological drought (characterized by the standardized precipitation evapotranspiration index) in upstream regions showed an upward trend on the short-term (1-month) scale. At the 6-month scale, human activities reduced hydrological drought events (characterized by the standardized streamflow index) at 93% of stations in the midstream and downstream reaches. (2) The proposed center of gravity method is more suitable for calculating the propagation time after the impact of human activities, while the onset method is suitable for early drought warning. (3) Human activities shortened the propagation time for the controlled area of about 58% of stations (11 out of 19) during the growing season and prolonged it for the controlled area of about 53% of stations (10 out of 19) during the nongrowing season in the Yellow River Basin. [ABSTRACT FROM AUTHOR]

Understanding the drought propagation from meteorological drought (MD) to hydrological drought (HD) can help assist in the drought early warning and reduce drought related losses. Propagation time is a significant variable in describing drought propagation. In this study, we identify the MD and HD using the three-dimensional drought identification method to reflect the drought characteristics over temporally continuous periods and spatially adjacent areas. Then, we calculate the drought propagation time by considering the spatio-temporal overlaps between MD and HD events, which can provide further insight to reveal the drought propagation process in both time and space. Specifically, we consider the propagation time of interval of the start (△T s), peak (△T p), and end (△T e) time between a paired MD event and HD event, respectively. The propagation process from MD to HD is investigated during 1961–2015 in the Yangtze River basin, China. Results indicate that the majority (>70%) of HD events are well matched with the majority (>70%) of MD events, and there are decomposed effect and joint effect during the propagation process from MD to HD. A stronger link between HD events and MD events with higher matching rate of MD and HD events is observed in autumn (SON) than the remaining three seasons. We find that the MD events in Yangtze River basin generally need 2 to 4 months to propagate to the HD events, and such response time from MD to HD events is becoming longer in most subbasins as the propagation time (△T s , △T p , and △T e) show a significant increasing trend. The results in our study can help understand the drought development and the drought propagation, and are also helpful for water managers to make rational water resources management decisions. • The propagation time from MD to HD is estimated in the perspective of three-dimension. • The propagation time mainly ranges from 2 to 4 months in the Yangtze River Basin, China. • The trend of propagation time is obvious in the 7 sub-basins when considering the different of spatial difference. [ABSTRACT FROM AUTHOR]

• Drought propagation characteristics are discussed over the Aral Sea Basin. • Drought propagation probability is interpreted by copula functions. • VBMC is applied to quantify the uncertainty during drought propagation. • Compared with MCMC, VBMC shows similar accuracy and superior efficiency. • The propagation probabilities tend to be underestimated without uncertainty impact. Agricultural drought (AD) is disastrous to natural and socioeconomic systems, and the propagation of meteorological drought (MD) plays an essential role in the occurrence of AD. However, how uncertainty affects the mechanism of propagation from MD to AD remains unclear. In this study, a novel method called C-VBMC is developed through coupling copula function with Variational Bayesian Monte Carlo (VBMC). The developed C-VBMC is then applied to the Aral Sea Basin to demonstrate its feasibility and capability. Results indicate that the method could effectively quantify the drought propagation probability under the impact of uncertainty. Several findings can be summarized: (1) compared with the low elevation areas, the propagation time and relationship between MD and AD tend to be longer and weaker in spring and winter at mid-high elevation areas; (2) drought propagation characteristics are significantly affected by seasonality, altitude, potential evapotranspiration, precipitation and soil moisture; (3) the posterior distribution of copula parameter by VBMC is similar with Markov chain Monte Carlo (MCMC), and VBMC only takes about 50% and 5% of the computation time required by MCMC for univariate and bivariate copula functions, the results highlight the superiority and flexibility of VBMC for large datasets; (4) the probability of AD occurrence and the uncertainty range are easily affected by same and more severe level MD; (5) the propagation probabilities tend to be underestimated without uncertainty impact, and the uncertainty range is lower than 0.05 for most grids. This study is helpful for drought warning management and disaster prevention systems. [ABSTRACT FROM AUTHOR]

The Threshold Level Method is an approach that enables comparability across all hydrological levels. This advantage is used especially in studies on drought propagation. There are different calculation procedures for this method. The effect that the choice of a variable versus a constant threshold level method has on drought characteristics and drought propagation patterns has not been fully explored yet. Also, most drought propagation studies have analyzed modelled data, suggesting that applicability to observations be tested. We tested the Constant and the Variable Threshold Level Method for the 10th, 20th and 30th percentile on observed precipitation, streamflow, and groundwater data from Germany, and compared drought characteristics and drought propagation patterns by means of statistical analysis and synoptic assessment. The characteristic effects of choosing a variable versus a constant threshold are: (1) a substantial increase in short droughts, (2) a moderate decrease in intermediate droughts and (3) a minor increase in long droughts. Furthermore, in slow-reacting lowland catchments, theoretical propagation characteristics could mostly be confirmed. In faster-reacting upland catchments, this was not always the case and considerable differences arose. Sources of ambiguity were predominantly groundwater in lowlands and streamflow in the mountainous catchments. In conclusion, there is potential of diverging inference from the same data, depending on the chosen methodology. [ABSTRACT FROM AUTHOR]

• The spatiotemporal continuity of droughts was explored using a three-dimensional clustering algorithm. • Droughts can migrate hundreds of kilometers from the source sites in the agro-pastoral ecotone of northern China. • The more severe and longer duration of meteorological drought, the more likely it is to trigger agricultural drought. Understanding the spatiotemporal evolution of droughts is critical for food security and water allocation. In this study, we propose an approach to construct the linkage of the propagation from meteorological drought to agricultural drought to explore the simultaneous spatiotemporal evolution of droughts based on a 3-dimensional clustering algorithm. We first evaluate the improvement of the downscaled high-resolution outputs from the Weather Research and Forecasting (WRF) model to reanalysis data in detecting wet-dry variations in the agro-pastoral ecotone of northern China (APENC). The WRF simulation results well characterize the evolution of droughts with a high correlation coefficient of 0.82 (p <0.05), which implies that the WRF downscaling model provides reliable hydrometeorological results for assessing and analyzing long-term wet-dry variations. Subsequently, we identify and track the spatiotemporal evolution of each individual drought event in the APENC for the first time. Based on the standardized precipitation index calculated from the WRF outputs, a total of 185 drought clusters were identified during 2000–2017, with 28 drought events lasting at least 3 months duration occurring in the APENC. The characteristics of the different drought events vary considerably. Droughts in the APENC have a larger percentage of propagation to the northeast and northwest and migrated hundreds of kilometers from the source sites. The results of the propagation of meteorological droughts to agricultural droughts indicate that 53.75% of the meteorological drought events progressed further to agricultural droughts. Agricultural droughts exhibit spatial variations consistent with meteorological droughts. Agricultural droughts have 1.69 months onset lag time, 2.12 months termination lag time, and overall longer duration than meteorological droughts in the APENC. Our findings provide valuable information for the mechanism and prediction of drought propagation. [ABSTRACT FROM AUTHOR]

• Drought propagation was re-examined by using three types of the propagation time. • An attribution framework was performed to quantify impacts of different factors. • Contribution rates are misjudged when ignoring climate change effects. • Climate change and large reservoirs mitigated drought while human activities exaggerated all drought characteristics. Enhancing the comprehension of hydrological drought evolution and drought propagation mechanisms is crucial for effective drought risk management in a changing environment. Previous studies have either inadequately considered the effects of climate change or conflated the impacts of large reservoirs and human activities. This study presents a comprehensive framework that integrates multiple comparison methods to quantify the effects of climate change, large reservoirs, and other human activities. The framework comprises three steps: (1) preparation of four types of streamflow based on critical time, large reservoirs inflow and outflow, and hydrological model; (2) estimation of hydrological drought characteristics, including duration, severity, peak intensity, instantaneous development speed, and instantaneous recovery speed and drought propagation characteristics, such as correlation, transition rate, and three types of the propagation time (PT) based on the start point (PT S), peak point (PT P), and end point (PT E); (3) quantification of the influences of various factors on the characteristic variables. The upper Yellow River Basin, a cold basin with large cascade reservoirs, was selected as the study area to utilize the proposed framework. The results revealed that climate change and large reservoirs reduced the duration and severity of drought events with relative contribution rates ranging from 146.6% to 340.2% and 381% to 707.7%, respectively, while those were increased by human activities with relative contribution rates from 428.0% to 1147.9%. Large reservoirs played the most crucial role in the development and recovery stages, with relative contribution rates of 75% and 85%, respectively. Climate change strengthened the correlation between the two drought indices, while human activities and large reservoirs weakened the correlation. The changes in three PT indicated that climate change shortened drought development and recovery period, while those were prolonged by human activities. Many hydrological droughts occurred before meteorological droughts due to large reservoir regulations. The changes in transition rates are −30.3%, 48.0%, and −28% under the influences of climate change, human activities, and large reservoirs, respectively. The framework and results of this study provide valuable insights into the mechanisms of hydrological drought and drought propagation and serve as a scientific basis for drought mitigation in changing environments. [ABSTRACT FROM AUTHOR]

Climate variation and anthropic activities are two key driving forces that impact the hydrologic cycle as well as the relationships between different drought types. Thus, it is essential to evaluate the impacts of environmental variations on the relationship between meteorological and hydrological droughts. In this study, abrupt changes in the yearly hydrological time series (streamflow) of the Han River Basin (HRB) were detected using a non-linearity-based empirical segmentation approach. The Standardized Precipitation Evapotranspiration Index (SPEI) was employed to model meteorological drought, while the Generalized Additive Model for Location, Scale and Shape (GAMLSS) algorithm was adopted to model the non-linear hydrological time series to obtain the non-stationarity based Standardized Runoff Index (SRI NS). Correlation analyses were conducted on meteorological droughts (as presented by SPEI) and the hydrological drought data (as presented by the SRI NS). A Bayesian network model (BNM) was employed to calculate the propagation likelihood of different categories of meteorological droughts resulting in hydrological droughts. Change points in the hydrological regime were identified based on the empirical segmentation analysis after the 1990s. Significant increasing trends in urbanization, gross domestic product, and population were observed after the change points. The correlation analysis showed that the seasonal (3-month) timescale of SPEI corresponded best to the three-month SRI NS. The BNM revealed that the average propagation likelihoods of severe and extreme categories of meteorological drought resulting in severe and extreme categories of hydrological drought were 23.6% and 18.2%, respectively, due to the influence of climate change. These probabilities were increased by 53.9% and 70.8%, respectively, in the human impacted era due to high pressure on water resources caused by increased population, industrialization, water extraction, etc. In conclusion, the likelihood of extreme conditions of meteorological drought resulting in extreme hydrological drought was increased significantly after the change points. • Novel framework to analyze the impact of environmental forces on drought propagation. • A non-stationary approach was proposed for change point detection in streamflow series. • Bayesian Network model to investigated propagation probability between SPEI and SRI NS. • Increase in drought propagation probability was observed in human induced period. [ABSTRACT FROM AUTHOR]

• Connections between meteorological and hydrological droughts (CMHDs) were assessed. • HD exhibited steeper downward trend, smaller number, and longer duration compared with MD. • Human activities weakened multiple aspects of CMHDs in the Yellow River basin. • Weakening CMHDs featured smaller correlation, larger difference, and less propagation rate. Connections between meteorological and hydrological droughts (CMHDs) have changed due to increasingly intensified human activities. Understanding such changes from an anthropogenic perspective is, therefore, of critical importance for drought monitoring, early warning, and adaptation. As the second-longest river system in China, the Yellow River basin (YRB) has been seriously impacted by humans and has a high risk of drought due to its dry climate, dense population and massive water demand. However, the effects of human activities on CMHDs in the YRB are still unclear. We thus used the standardized precipitation evapotranspiration index (SPEI) and the standardized streamflow index (SSI) to indicate meteorological drought (MD) and hydrological drought (HD), respectively, and analysed CMHDs with multiple indicators including trends, correlation, difference, and drought propagation characteristics. Our results highlighted the heterogeneity of CMHDs in terms of subregions and indicators and showed that this heterogeneity was impacted by humans by quantifying the effects of human activities (mainly referring to water abstraction and regulation) on CMHDs in each subregion. We found that 1) human activities aggravated the disconnections between MD and HD by sharpening the downward trend in the SSI and weakening the correlation (amplifying the difference) between the SPEI and SSI, and 2) human activities reduced the drought propagation rate from MD to HD, manifested by a decreased number of HD but a lengthening of the HD duration. In addition to the abovementioned effects that were consistent for most of the YRB, there were also some effects, for example, on HD intensity and drought propagation time, that differed among subregions, and these kinds of diverse responses of CMHDs might be related to the various human activities in terms of intensities, types, and regions. By analysing human effects on CMHDs, this study may be helpful in understanding drought and drought propagation in the Anthropocene, which is beneficial to watershed management. [ABSTRACT FROM AUTHOR]

Research on drought propagation is of great significance for the scientific prediction of agricultural drought and reducing drought losses. In this study, based on the daily scale standardized precipitation evapotranspiration index (SPEI) and soil water deficit index (SWDI), the effects of irrigation and groundwater level change on the development and spread of drought were studied, and the dynamic change in the spread time from meteorological drought to agricultural drought was explored through a sliding window. Additionally, the critical value of the response of agricultural drought to meteorological drought was calculated. The results indicated that (1) under Scenario-1 (groundwater depth 19.4 m, no irrigation), Scenario-2 (groundwater depth 2 m, no irrigation), and Scenario-3 (groundwater depth 19.4 m, irrigation), the lag times of agricultural drought on meteorological drought were 23 d, 42 d, and 30 d, respectively. (2) The drought propagation time under Scenario-1 and 2 exhibited a significant upwards trend. According to the factor contribution rate and cross-wavelet analysis, the rising trend of the Arctic Oscillation (AO) and the decreasing trend of the Pacific Decade Oscillation (PDO) led to the shortening of sunshine duration, which was the key reason for the extension of drought propagation time. (3) Under Scenario-1, the critical values of the agricultural drought response to meteorological drought duration and intensity were 4.9 and 0.9, respectively. Under Scenario-2, the critical values increased to 5.1 and 2.0, revealing that the propagation of meteorological drought to agricultural drought would slow down when groundwater rose to an appropriate position. • Irrigation and suitable groundwater levels curtail drought spread. • The drought spread time shows an upward trend in the past 60 years. • Shorter sunshine duration is key to curtail drought spread. • Drought thresholds increase after the rise of groundwater level. [ABSTRACT FROM AUTHOR]

[Display omitted] • A framework for quantifying the effects of wetlands on hydrological droughts is proposed. • Wetland effects on drought characteristics and propagation of meteorological to hydrological droughts were determined using a hydrological modeling platform. • Wetlands can mitigate the development process, accelerate the recovery, shorten the duration and alleviate the severity of hydrological droughts. • Wetlands can extend the propagation time and weaken the transition from meteorological to hydrological drought. Wetlands have been singled out as a potential nature-based solution for improving the resilience and reducing the risks of hydrometeorological extremes. However, whether and to what extent wetlands can affect hydrological droughts is not well understood. To fill this gap, we proposed a general framework to discern the effect of wetlands on: (i) the characteristics (duration, severity, development and recovery processes) of hydrological droughts, and (ii) the propagation of meteorological droughts to hydrological droughts. First, hydrological modeling was conducted with a spatially-explicit model integrated with wetland modules. Then, the run theory and pooling method were selected to recognize hydrological drought events and identify their characteristics. Further, the Pearson correlation coefficient, temporal shift method and cross wavelet transform were used to explore the propagation processes. Finally, the characteristics and propagation processes were compared to quantify wetland mitigation services on hydrological droughts. To validate the proposed framework, two river basins from China and Canada (the Gan River Bain and the Nelson River Bain), with distinct land cover, were chosen to perform hydrological modeling and quantify wetland effects. The results indicate that wetlands mainly contribute to alleviating hydrological droughts by decelerating the development process, accelerating the recovery, shortening the duration, and reducing the severity of the hydrological drought events. However, the effects are variable as they may have weak impacts and even worsen drought conditions. Wetlands can extend drought propagation time and weaken the transition of meteorological to hydrological droughts. The likelihood of hydrological drought formation due to meteorological decreased by 19% and 18% respectively, for the Gan River Bain and Nelson River Bain, thanks to the mitigation services of wetlands. These findings highlight the drought-mitigation roles of wetlands and the proposed modelling framework has the potential to be useful in beneficial in assisting basin management on drought risks in the context of climate change mitigation. [ABSTRACT FROM AUTHOR]

• The mechanism of triggering and driving drought propagation differs. • Triggering drought propagation highly relies on meteorological drought patterns. • Driving drought propagation is primarily depends on underlying surface. • Meteorological and hydrological drought condition will intensify in future scenarios. Exploring the propagation from meteorological drought to hydrological drought and its potential influence factors is crucial for early warning of hydrological drought. As a case study in the Xijiang River Basin (XRB), South China, the Standardized Precipitation Index (SPI) and Standardized Runoff Index (SRI) series from 1961 to 2013 were used to represent the meteorological drought and hydrological drought with daily runoff generated by VIC model. An identification process for the threshold and the mechanism of drought propagation was conducted based on rank order analysis and Copula theory. The drought propagation regulations of drought variables, geographical location, and lag-time were established by linear or non-linear functions. Eventually, the propagation regulations were applied to the hydrological drought prediction from 2021 to 2050. Results indicated that: (1) The spatial-temporal patterns of meteorological drought are the critical factors in triggering drought propagation, and the effects of meteorological drought area, drought severity, drought duration, drought spatial concentration, and drought persistent duration increase successively. The critical threshold for triggering drought propagation is the combined frequency of the above five drought variables greater than 0.14. (2) The geographic location, center number, duration, severity, and area of two drought types follow the linear, two-piecewise, power, linear and logarithmic functions, respectively. Drought mainly propagation from west to east in three-dimensional space, and the lag-time was less than three months, with the maximum being 78 days. Unlike triggering drought propagation, driving drought propagation is synthetically associated with meteorological, soil water, groundwater, and topography conditions. (3) Under the MRI-ESM2-0 model, the severity and area of hydrological drought under different scenarios in the 2021–2050 will increase compared with the reference period 1961–2013, and the extreme hydrological drought exceeding history may occur under scenarios SSP1-2.6, SSP2-4.5, and SSP5-8.5. The findings can help policy-makers manage the early stages of hydrological drought based on meteorological drought conditions and thus reduce the negative impact of drought hazards. [ABSTRACT FROM AUTHOR]

Meteorological drought is generally regarded as the cause of other types of droughts. This study firstly analyzed the characteristics of meteorological drought and hydrological drought in different climate regions all over the world during a long time period (1902–2014); then, the maximum Pearson correlation coefficients (MPCC) of meteorological drought and hydrological drought at different time scales were calculated to determine the drought response time (DRT) in each climate region. The results revealed that: 1) meteorological drought in most climate regions intensified during 1902–1958 but showed a wetting trend during 1959–2014. Compared with the characteristics of meteorological drought, the change of hydrological drought was slightly different. Hydrological drought weakened during 1902–1958 but intensified slightly during 1959–2014; however, the magnitude of the changing rate was relatively small. 2) The drought response relationship in the Cf (i.e., continental wet warm) climate region was the strongest, and that in the E (i.e., polar) climate region was the weakest. 3) Globally, the DRTs in various climate regions were mainly 5–10 months, which were mainly related to the climate type. The outcomes of this study can provide a reference for further revealing the propagation mechanism from meteorological drought to hydrological drought in different climate regions. • Global meteorological drought showed a wetting trend during 1902–2014. • Global hydrological drought had no trend during 1902–2014. • Drought response relationships in humid climate regions were more significant. • Drought response time was closely related to climate type. [ABSTRACT FROM AUTHOR]

Subsurface storage changes (Δ S) represent a key modulator of drought propagation through the hydrological cycle, but their contribution to the annual water balance, and to drought propagation and recovery has rarely been explicitly assessed across catchments and climates. To expand on previous work on this matter, here we performed a large-sample analysis of precipitation, discharge, actual evapotranspiration (ET), and Δ S for 10 hydrological years and 102 catchments across various hydro-climatological regimes in Italy. We found that Δ S cannot be neglected in the annual water balance. Storage depletion leads to the attenuation of hydrological drought compared to meteorological drought, meaning that subsurface storage actively supports discharge during drought. We also found that storage generally recovers from precipitation deficits over time scales similar to the discharge recovery time, while recovery times for ET are longer. These findings show that subsurface storage drives drought propagation and recovery, regardless of climatic and catchment characteristics, and are thus relevant to properly inform water managers about surface- and ground-water availability in a changing climate. • Large-sample analysis of water balance components to study drought propagation and recovery. • Subsurface storage changes account on average for the 11% of long-term mean annual precipitation across the catchments. • Subsurface storage depletion sustains discharge during drought and the following recovery period. • A water balance approach is needed to better understand drought propagation and recovery. [ABSTRACT FROM AUTHOR]

It is of importance to investigate the response of agricultural drought to meteorological drought and its influencing factors, which could help better understand drought evolution mechanisms and facilitate agricultural drought monitoring and predictions. As a case study in the Wei River Basin (WRB), China, the heuristic segmentation method was first applied to identify change points of long-term hydrological and metrological conditions for the period of 1960–2007. Then the cross wavelet analysis was utilized to reveal the detailed links between agricultural drought (based on Palmer Drought Severity Index (PDSI)) and meteorological drought (based on Standardized Precipitation Index (SPI)) at the seasonal time scale. The controlling factors governing the agricultural response were then explored through quantitatively examining the corresponding large-scale atmospheric conditions and local-scale land surface characteristics. Results indicate that: (1) the variations of the lag time of agricultural drought in response to meteorological drought is large at the seasonal scale, characterized by fast response in summer and relatively slow response in autumn, and the contrasting response in the time lag is mainly due to the buffering effects of soils; (2) the variations of Arctic Oscillation (AO) was found to have large effects on the lag time, with both positive and negative effects; (3) a negative correlation between the lag time and the parameter w in the Fu’ equation within the Budyko framework was found, implying the potential effects of vegetation cover on the drought propagation from meteorological drought to agricultural drought in the WRB. [ABSTRACT FROM AUTHOR]

This paper explored the drought propagation phenomenon based on meteorological, hydrological, and agricultural aspects in the Yangtze River basin (YRB), China. To evaluate meteorological, hydrological, and agricultural droughts, this paper used three drought indices, standardized precipitation evapotranspiration index (SPEI), standardized runoff index (SRI), and standardized soil moisture index (SSMI), respectively. The community land model (CLM) in the YRB to generate the monthly evapotranspiration, soil moisture, runoff data, which are required for the estimation of drought index, were applied. Different mean durations (6-and 12-month) were used for drought estimation, and propagations of meteorological to hydrological and meteorological and agricultural droughts were investigated for different durations as SPEI6-SRI6, SPEI6-SSMI6, SPEI12-SRI12, SPEI12-SSMI12. The average drought propagation between 1950 and 2010 presented the highest autocorrelation and correlation with one-month lags in four combinations of drought indices in SPEI6-SRI6, SPEI6-SSMI6, SPEI12-SRI12, and SPEI12-SSMI12. Additionally, this paper estimated the optimal lags of SPEI-SRI and SPEI-SSMI drought propagations using mean 6-and 12-month lag times for six representative drought periods. Therefore, the propagation phenomenon of meteorological to hydrological and to agricultural droughts were confirmed in the YRB. • SPEI, SRI, and SSMI indices have been applied to the Yangtze River basin (YRB). • Propagation analysis of SPEI-SRI and SPEI-SSMI have extended to 1951–2010. • Mean 12-month duration shows clearer drought propagation than mean 6-month duration. • SPEI-SSMI presents 1–7 months propagation time. • SPEI-SRI presents 1–2 months propagation time. [ABSTRACT FROM AUTHOR]

[Display omitted] • Local-scale drought propagation is performed over India at a grid resolution of 0.5° × 0.5° using multiple runoff datasets. • The influence of external drivers on meteorological and hydrological drought indices are evaluated. • The locations with high value of DDP are associated with high value of DRP. • The propagation time with respect to initiation to initiation is shorter than peak to peak and termination to termination. • The drought propagation characteristics are underestimated when the influence of external drivers are not considered. As a costliest natural hazard, drought profoundly affects water resources, agriculture, and socio-economic sectors in India. In spite of large spatio-temporal variability in droughts, the propagation time from meteorological to hydrological droughts is not examined at local scale over India. In this study, the meteorological and hydrological variables are obtained at a grid resolution of 0.5° Lat × 0.5° Lon over India to estimate the time of propagation. Here, five different runoff datasets from ERA5, FLDAS, GLDAS, MEERA2, and NCEP are collected. The Standardised Precipitation Evapotranspiration Index (SPEI), and Standardised Runoff Index (SRI) are estimated under the influence of external global and regional drivers. The drought propagation time is computed in 1170 grids blanketing the entire India based on differences between the initiation to initiation (Δs), peak to peak (Δp) and termination to termination (Δe). In addition, the internal propagation of hydrological drought is estimated with the help of variable motion relationship of speed-time process. The large duration and more severe hydrological droughts are observed mostly over southern and northern parts of India. The drought propagation time varies between 4 and 9 months, 9 to 12 months, and 15 to 20 months in the cases of Δs, Δp, and Δe, respectively. The drought development and recovery duration are computed as 3.1 to 6 months over most of the areas. It is found that locations with the high value (greater than 10 months) of Drought Development Period (DDP) are also having high value of Drought Recovery Period (DRP). The internal propagation of hydrological drought ranges between the magnitude of 0.4 and 0.6 per month over most of the area in India. It is found that the drought propagation and its characteristics are underestimated over most of the regions in India when computed without the external drivers. The present study would provide important drought characteristics at local scale which can assist water managers and policy makers to devise sustainable management practices. [ABSTRACT FROM AUTHOR]

• WRF-Hydro is used to calculate hydrological and agricultural drought indices. • Durations of meteorological droughts are much shorter than those of other types. • Attenuation observed during propagation from meteorological to hydrological drought. • No attenuation occurred in propagation from meteorological to agricultural drought. Drought is a complex and slow-moving disaster that is difficult to monitor and define. This study, therefore, aims to demonstrate the characteristics of recent droughts occurring from 2008 to 2015 over South Korea using a process-based land and hydrologic model, Weather Research and Forecasting-Hydro modeling system (WRF-Hydro). To drive the standalone WRF-Hydro, gridded meteorological data (5 km) were generated using station-based observations and the Parameter-elevation Regressions on Independent Slopes Model (PRISM). The model was calibrated and evaluated using inflow observations at four locations with dams; for 2008–2010 (calibration) and 2011–2015 (evaluation), it demonstrated average R2 values of 0.80 and 0.75, respectively. While Standardized Precipitation Index is used for calculating meteorological drought using precipitation from PRISM, Standardized Soil Moisture Index and Standardized Streamflow Index, at different timescales, are used to calculate agricultural and hydrological droughts, respectively, with WRF-Hydro simulations. The correlation coefficients between SPI and both SSFI and SSMI were calculated to detect their response times. The hydrological and agricultural droughts showed response times 0.5–1 month later than meteorological drought. In 2008–2015, agricultural and hydrological drought events occurred 1.6 times per year on average in South Korea, whereas meteorological droughts occurred 4.3 times per year on average. Agricultural and hydrological droughts lagged behind meteorological droughts by up to 53, 65, and 83 days, when using 1-, 3-, and 6-month SPI, respectively. Moreover, hydrological droughts were less severe than meteorological droughts due to the propagation of drought by attenuation. This study demonstrates that WRF-Hydro can be used to quantitatively determine the different types of drought events and their propagation, which could help policy makers manage drought risks. [ABSTRACT FROM AUTHOR]

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Summary: Drought may affect all components of the water cycle and covers commonly a large part of the catchment area. This paper examines drought propagation at the catchment scale using spatially aggregated drought characteristics and illustrates the importance of catchment processes in modifying the drought signal in both time and space. Analysis is conducted using monthly time series covering the period 1961–1997 for the Pang catchment, UK. The time series include observed rainfall and groundwater recharge, head and discharge simulated by physically-based soil water and groundwater models. Drought events derived separately for each unit area and variable are combined to yield catchment scale drought characteristics. The study reveals relatively large differences in the spatial and temporal characteristics of drought for the different variables. Meteorological droughts cover frequently the whole catchment; and they are more numerous and last for a short time (1–2months). In comparison, droughts in recharge and hydraulic head cover typically a smaller area and last longer (4–5months). Hydraulic head and groundwater discharge exhibit similar drought characteristics, which can be expected in a groundwater fed catchment. Deficit volume is considered a robust measure of the severity of a drought event over the catchment area for all variables; whereas, duration is less sensitive, particular for rainfall. Spatial variability in drought characteristics for groundwater recharge, head and discharge are primarily controlled by catchment properties. It is recommended not to use drought area separately as a measure of drought severity at the catchment scale, rather it should be used in combination with other drought characteristics like duration and deficit volume. [Copyright &y& Elsevier]

Droughts grow concurrently in space and time; however, their spatiotemporal propagation is still not fully studied. In this study, drought propagation and spatiotemporal characteristics were studied in northern, northeastern, and central Thailand (NNCT). The NNCT is an important agricultural exporter worldwide, and droughts here can lead to considerable pressure on the food supply. This study investigated meteorological drought and soil drought in northern Thailand and identified 70 meteorological drought events and 44 soil drought events over 1948–2014. Severe droughts (droughts with long trivariate return periods) mainly occurred after 1975 and were centered in northern and northeastern Thailand. Meteorological drought and soil drought that occurred during 1979–1980 had the longest trivariate return periods of 157 years and 179 years, respectively. The drought centers were mainly located in the Chao Phraya River basin and the Mun River basin. The mean propagation ratios of all drought parameters (duration, area, severity) were lower than 1, indicating that the underlying surface can serve as a buffer to alleviate water deficits. Most of the probability distribution coefficients and all drought propagation ratios of the three drought parameters were found to change significantly based on a moving-window method, indicating that the drought parameters and propagation from meteorological drought to soil drought were non-stationary. Significant increasing trends were detected in mean values of most drought parameters, ranging from 2.4%/decade to 16.6%/decade. Significant decreasing trends were detected in coefficients of skewness (Cs) of all drought parameters and coefficients of variation (Cv) of most drought parameters, ranging from −3.3 to −12.4%/decade, and from −5.5 to −19.4%/decade, respectively. The propagation ratios of all drought parameters showed significant increasing trends, indicating that the function of the underlying surface as a buffer has become weaker. The drought propagation ratios were found to be positively related to two climate indices, the phase index (PI) and the climate seasonality index (CSI). These findings will help to develop a better understanding and management of water resources in Thailand. [ABSTRACT FROM AUTHOR]

• Compound drought is evaluated via a framework from a drought propagation perspective. • The simultaneous occurrence of meteorological and hydrological drought is considered. • Gaussian-copula function was the best function for characterizing compound drought. • Reservoir regulation can reduce compound drought duration and severity. Compared with a single drought event, compound drought (i.e., two or more droughts occurring simultaneously) has more substantial effects on economic growth, water resources, and the ecological environment. A useful framework for assessing compound drought events from a drought propagation perspective was proposed. The framework includes the definition, identification, and risk assessment of compound drought. We defined compound drought as a drought event from a drought propagation perspective when meteorological drought and hydrological drought occur simultaneously. The Standardized Streamflow Index (SSI) and Standardized Precipitation Index (SPI) were used to represent hydrological and meteorological drought, respectively. By applying a certain truncation threshold of run theory, the compound drought events in the time series were identified and characterized according to their duration and severity. Five univariate distribution functions (i.e., Log-normal, Exponential, Gamma, Weibull, and Pareto) and four bivariate copula models (i.e., Gaussian, Clayton, Frank, and Gumbel) were used for fitting both the duration and severity of compound drought and their joint return periods. A 40-year monthly streamflow and precipitation dataset from the Dongjiang River Basin, which is located on the southern coast of China, was used as a case study. The characteristics of compound drought, including duration and severity, were captured by considering the time continuity of meteorological and hydrological droughts from a drought propagation perspective based on run theory. The most severe compound droughts in the study area were observed in 1963 and 2004–2005. The characteristics of compound drought duration and severity were related to the timescale of the drought index (i.e., SSI and SPI). For the study basin, the SPI at a 2–3-month timescale better matched the SSI on the monthly timescale compared with other timescales. The Gaussian-copula function better characterized the joint return periods between the duration and severity of compound drought compared with three other copula models. Although reservoir regulation played an important role in decreasing the duration (lower by 8.25%) and severity (lower by 9.27%) of compound drought, it had little effect on extreme compound drought events. Overall, the results indicated that the proposed method provides a useful tool for statistical assessments of compound drought from a drought propagation perspective. This framework could also be applied to other regions. [ABSTRACT FROM AUTHOR]

• Impact of TGD construction on drought propagation process were quantified. • Propagation of drought duration and severity were aggravated after TGD operation. • Hydrological drought and soil moisture drought propagation speed was affected. • Potential influence factors were explored at different periods from 1981 to 2020. The construction of Three Gorges Dam (TGD) has exerted substantial effects on local hydrological regime and eco-system since its operation in 2003. Due to this significant anthropogenic activity, drought propagation processes from Meteorological drought to Hydrological (M-H) and Soil moisture (M-S) drought are inevitably modified. However, current studies are still insufficient to answer whether the TGD operation mitigated or exacerbated the drought propagation process due to its complex impacts. To explore this key issue, this study proposed an integrated framework to quantify the impact of TGD construction on drought propagation process in the Yangtze River Basin (YRB). The drought characteristics propagation models and propagation time were calculated to identify the modification of drought propagation process between different TGD operation scenarios. Trend and attribution analyses were also utilized to explore potential influence factors. Results demonstrated that TGD construction did significantly aggravate the drought characteristics propagation. Specifically, the slopes of hydrological drought duration and severity in linear propagation models increased 23.98% and 29.23% in average. While for M-S propagation, the slopes of duration and severity models increased 28.72% and 21.91%, respectively. This research also found that, after TGD operation, the M-H propagation speed had been slowed down but the M-S lag time became shorter. Additionally, the variations and trend patterns of six potential influence factors at four separate periods were full analyzed to provide implications for the drought propagation modifications. And TGD operation was confirmed to become a major factor inducing the variations of annual runoff, which accounted for 56.75% for the entire YRB. The above quantitative findings are expected to reveal the potential changes of drought propagation process caused by the construction of TGD in YRB. The proposed integrated framework is also beneficial to the drought early warning system and understanding of drought development not only in YRB, but also in other basins at the global scale. [ABSTRACT FROM AUTHOR]

• A diagnosis frame was proposed to assess the reservoir impacts on drought propagation. • Strong aggravating effect of reservoir on drought propagations was detected. • The mechanism of reservoir influencing drought propagation was analyzed. Human interventions (HI) are significantly affecting the land surface hydrological cycle, and thus altering the occurrence of hydrological drought. So far, however, how HI affect the propagation from meteorological to hydrological drought is still unclear. In this study, we proposed a quantitative diagnosis framework and assessed the impacts of HI on drought propagation across varying scales over the typical reservoir-dominant Daling River basin (DRB) in China, in which the Standardized Precipitation Index (SPI) and Standardized Streamflow Index (SSI) were utilized to identify the meteorological drought (MD) and hydrological drought (HD), respectively. Our results show that the in-situ streamflow records were found with an evident turning point around 2003, coincident with the operation of the largest reservoir in DRB. Under the influence of reservoir operation, the HD frequency saw an obvious intensification and the correlations between MD and HD exhibited a decreasing tendency, especially during the wet season. The seasonality of drought propagation changed significantly for both up-downstream and MD-HD, as indicated by the advance of drought events from autumn to summer and the aggravation of autumn drought. The reservoir operation changed the HD events characteristics by increasing the drought duration and severity. Our results highlight the strong aggravating effect of reservoirs on drought propagation. [ABSTRACT FROM AUTHOR]

• Correlation and propagation among meteorological, agricultural and groundwater droughts are firstly explored in the Yangtze River Basin and the Yellow River Basin. • The propagation time from meteorological to agricultural drought in the Yangtze River Basin is longer than that in the Yellow River Basin. • There is a weak linkage between groundwater drought and meteorological/agricultural drought in the two selected basins, especially in the Yellow River Basin. • Groundwater extraction is a noticeable factor triggering groundwater drought in the two basins. The propagation of meteorological drought in the hydrological cycle not only leads to the deficits of surface soil moisture, which results in agricultural drought, but also probably affects groundwater to trigger groundwater drought. Improving the understanding about the correlation and propagation among meteorological, agricultural and groundwater droughts is necessary to lessen the risks resulted from them. Moreover, the distinction of the correlation and propagation over the basins with different climate conditions is not yet sufficiently understood. As a case study of the humid and arid/semi-arid basins in China, the standardized precipitation index, the standardized soil moisture index and groundwater drought index based on GRACE (Gravity Recovery and Climate Experiment) are used to characterize meteorological, agricultural and groundwater drought respectively over the Yangtze River Basin with a humid climate condition and Yellow River Basin with an arid/semi-arid climate condition. The Spearman rank correlation coefficient is applied to investigate the correlation and propagation among the above three types of drought in the two basins. The results indicated that: (1) The meteorological, agricultural and groundwater droughts in the Yangtze River Basin and the meteorological and agricultural droughts in the Yellow River Basin are decreasing from April 2002 to March 2020, while the groundwater drought in the Yellow River Basin is aggravating in recent years. (2) There is a strong link between meteorological and agricultural droughts, and the propagation time from meteorological to agricultural drought in summer and autumn is shorter than that in winter and spring in the two basins. When comparing the propagation time in the two selected basins, it is longer in the Yangtze River Basin. (3) Groundwater extraction may be the main factor in the aggravation of groundwater drought in the two basins, which is different from the contributors to agricultural drought, which is mainly the propagation of meteorological drought. [ABSTRACT FROM AUTHOR]

• An observation-based natural and human-impacted catchment comparison method is proposed. • Human influence are quantified based on gridded socio-economic and land use data. • Climatic and anthropogenic influences on drought propagation are investigated. • Climate change accelerates the response of hydrological drought to meteorological drought. • Human activities delay the propagation from meteorological to hydrological drought. It is crucial to investigate how a precipitation deficit is transformed into hydrological drought and how climate change and human activities affect this transformation process, which is helpful to gain a deep understanding of drought propagation process in this changing environment. This study proposed an observation-based natural and human-impacted catchment comparison method to assess the impacts of climate change and human activities on propagation from meteorological drought to hydrological drought. The method mainly consists of the following three steps: (1) selection of natural catchments through analysis of trends and change points of hydro-meteorological data, as well as statistics analysis of human influence based on land use and socio-economic indicators data sets; (2) calculation of drought propagation characteristics (e.g., drought severity, duration, and propagation time) based on run theory and the Pearson correlation coefficient; and (3) comparison of drought propagation characteristics of natural catchments between undisturbed and disturbed periods to identify the impacts of climate change on drought propagation, and comparison of the propagation characteristics between natural and human-impacted catchments during the disturbed period to investigate human influence on drought propagation. The Laohahe basin (with eleven sub-catchments), located in northern China, was evaluated via the proposed procedure, and standardized precipitation index (SPI) and standardized runoff index (SRI) were used to characterize meteorological and hydrological droughts, respectively. The results demonstrate that the proposed method is suitable tool for distinguishing natural and human-impacted catchments, and separating the impacts of climate change and human activities on drought propagation. Furthermore, the comparison results of different schemes show that climate change accelerates the propagation from meteorological drought to hydrological drought in the Laohahe basin, shortening it by approximately 3 months. Human activities, however, disturb and then delay the natural propagation from meteorological drought to hydrological drought, retarding it by 11–12 months. Although the Laohahe basin was selected as a case study in this paper, the proposed method can be applied in other regions as well to improve drought prediction and water resources management. [ABSTRACT FROM AUTHOR]

• We propose a copula-based model for linking meteorological drought and soil moisture drought. • Seasonal cumulative water deficit and initial soil moisture condition have different effects on drought propagation globally. • South America is more vulnerable to agricultural drought under the condition of meteorological drought. With a copula-based probabilistic model, this study presents a global view on the propagation of meteorological to soil moisture drought. Meta-Gaussian and three-dimensional vine copulas were employed to construct the bivariate and trivariate conditional joint drought distributions, respectively, using the time series of standardized precipitation evapotranspiration index (SPEI) and standardized soil moisture index (SMI) derived from the Global Land Data Assimilation System (GLDAS) simulations. Three different cases, including the probability and magnitude of soil moisture drought (SMI) conditioned on 1-month meteorological drought (SPEI1), seasonal meteorological drought (SPEI3), and the joint effects of SPEI1 and antecedent soil moisture conditions (SMI lag-1), were analyzed. Then, the duration of soil moisture drought in response to meteorological drought, and potentially affected cropland area were analyzed to assess potential agricultural impacts. Results showed that the likelihood of soil moisture drought conditioned on SPEI1 in the Amazon rainforest, southern and eastern China, Southeast Asia, southeastern United States, and west Africa was generally higher than in other regions. Under the impact of seasonal meteorological drought, except for the Qinghai-Tibet Plateau in China, northern Russia, and North Africa, the probability of soil moisture drought occurrence overall increased with significant increments in Europe and North America. The antecedent soil moisture condition also influenced the probability of drought propagation, and this effect was particularly significant for Northern China, Russia, the U.S. Midwest, Canada, and Australia. Spatially, the western U.S., northern Canada, South Africa, eastern Europe, North China, northern Russia, and most parts of Australia present longer duration of soil moisture drought in response to meteorological drought. Comprehensive considerations of the conditional probability, duration, and potentially affected area of soil moisture drought for croplands revealed that among five continents, South America was more vulnerable to agricultural drought under the condition of meteorological drought. [ABSTRACT FROM AUTHOR]

• Recovery of hydrological droughts can be 4 times longer than that of meteorological ones. • Recovery time is longest and more severe in dry regions and regions with high water use. • A multi-indicator approach is key to the proper characterization of drought development and propagation. Meteorological droughts propagate through the hydrological cycle causing hydrological droughts and societal impacts. However, the effects of climate and basin characteristics on hydrologic drought propagation vary regionally and remain largely unclear. In this paper, we characterize meteorological and hydrological droughts in 457 basins in Brazil. Using the Standardized Precipitation Evapotranspiration Index (SPEI) and Standardized Streamflow Index (SSI), we investigate hydrologic drought propagation based on differences in drought onset, the center of mass, and time to peak. Additionally, we estimate the recovery time of meteorological and hydrologic drought events. The results indicate that hydrological droughts are usually more long-lasting, severe, and with a slower recovery time compared to meteorological droughts. While the most severe meteorological droughts are observed in humid regions (e.g., Amazon and Southern Brazil), the most severe and long-lasting hydrological droughts are found in the driest region (i.e., Northeast Brazil) or mostly impacted by human activities (i.e., Southeast Brazil). Hydrological droughts in dry regions can take four times longer to recover than meteorological ones. For most regions, the propagation time was slightly different considering the different approaches. Our results highlight the importance of a multi-indicator approach to fully characterize the mechanisms controlling the development and propagation of droughts through the water cycle. [ABSTRACT FROM AUTHOR]

Agricultural drought is generally defined as a deficit in soil moisture, and can affect plant growth and crop yields. Accurate prediction of agricultural drought with sufficient lead time can aid agricultural planning and reduce losses in agricultural production. In this study, the meta-Gaussian model was employed to predict agricultural drought (standardized soil moisture index, or SSI) during spring and summer in China based on the initial soil moisture conditions, antecedent meteorological drought (standardized precipitation index, or SPI) and large-scale drivers (El Niño-Southern Oscillation, or ENSO). Monthly precipitation and soil moisture data from Global Land Data Assimilation System, version 2 (GLDAS-2.0) were used to compute the meteorological and agricultural drought indicators. The conditional distribution of agricultural drought given multiple predictors was used for the statistical prediction. The autocorrelation of agricultural drought, the correlation between meteorological drought and agricultural drought, and the correlation between ENSO and agricultural drought were first evaluated to understand the predictors from soil moisture persistence, drought propagation, and large-scale drivers. We then employed the conditional distribution to predict agricultural drought over the period from 1948 to 2014, in which contributions of antecedent meteorological drought and large-scale drivers to the prediction performance were evaluated. Results showed that the prediction method performed well in semi-arid and sub-humid regions during spring, but did not perform well in humid regions during summer. In addition, the incorporation of ENSO provided useful predictability for long lead time prediction in certain regions (with significant influence of ENSO). The results obtained from this study can provide useful information for early agricultural drought warning across China. • Predict agricultural drought in China based on meta-Gaussian model. • Evaluate multiple predictors during spring and summer. • Quantify impacts of drought propagation and large-scale drivers on prediction performance. [ABSTRACT FROM AUTHOR]