Drought Development Research Articles

Climatology and Composite Evolution of Flash Drought over Australia and Its Vegetation Impacts

Abstract This study describes flash drought (FD) inferred from the evaporative stress index (ESI) over Australia and its relationship to vegetation. During 1975–2020, FD occurrence ranges from less than 1 per decade in the central arid regions to 10 per decade toward the coasts. Although FD can occur in any season, its occurrence is more frequent in summer in the north, winter in the southern interior and southwest, and across a range of months in the far southeast and Tasmania. With a view toward real-time monitoring, FD “declaration” is defined as the date when the ESI declines to at least −1, i.e., drought conditions, after at least 2 weeks of rapid decline. Composite analysis shows that evaporative demand begins to increase about 5–6 weeks before declaration with an increase in solar radiation, while evapotranspiration initially increases with evaporative demand but then decreases in response to the soil moisture depletion. Solar radiation increases simultaneously with precipitation deficit, both reaching their peak around declaration. FD intensity peaks with soil moisture depletion, 2–3 weeks after declaration. The composite wind speed only shows a modest increase around declaration. The composite FD ends 4 weeks after rapid decreases in solar radiation and increases in precipitation. Satellite-derived vegetation health composites show pronounced decline in the nonforested regions, peaking about 4–8 weeks after FD declaration, followed by a recovery period lasting about 12 weeks after flash drought ends. The forest-dominated regions, however, are little impacted. Modeled pasture growth data show reduced values for up to 3 months after the declaration month covering the main agricultural areas of Australia. Significance Statement Flash drought describes a fast intensification or rapid development of drought conditions with potential severe impacts on agriculture and ecosystems. This study describes the climatology and typical evolution of flash drought over Australia for the period 1975–2020. An objective definition of flash drought, using high-resolution observational-based datasets, is proposed and its spatiotemporal variability is provided, as well as its relationship with vegetation health and pasture growth. This constitutes a guideline for understanding flash drought in Australia and its impacts on vegetation.

Spatio-temporal dynamic evaluation of agricultural drought based on a three-dimensional identification method in Northwest China

Drought evolution is a complex dynamic process, showing continuous characteristics in space-time. Currently, the researches on drought dynamics from multiple dimensions are limited and should be improved further. Therefore, a three-dimensional identification method was adopted to investigate the spatiotemporal patterns of classified drought events (namely two-month drought events, within-year drought events, and cross-year drought events) in northwest China during1961–2018. Furthermore, more spatial variables of drought event, such as start and end location, drought orientation and rotation, were extracted to describe the dynamic migration trajectories of drought events. Significantly, drought rotation helped to reveal the forcing mechanisms (such as the influence of climate and land surface) behind their spatial development. The results showed that a total of 169 drought events were identified over 1961–2018, and drought variables (duration, area, severity, and migration distance) represented fluctuating decreasing trend with the rate of − 0.135/10a, − 0.006/10a, − 0.16/10a, and − 5.67/10a. The dynamic migration process of individual drought event was objectively and effectively depicted from a three-dimensional perspective, which was consistent with the historical drought records in study area. Regarding the classified events, drought magnitude was more severe in 1961–1980 than that in 1981–2018, and three primary migration patterns (east-to-east, west-to-west, and south-to-south) were identified in northwest China. Within-year drought events mostly started in the first three quarters and finished in the second half year, whilst the situation was reversed for the cross-year drought events. Spatially, Alxa League of Inner Mongolia and northwest Qinghai Province were two main drought centers. Additionally, drought events characterized by clockwise rotation migration were mostly distributed in the plateau and southeast climate zones, and that was anticlockwise rotation in the westerly climate zone. Noticeably, the east-to-east pathways were mainly located in the east part of the study area, while the west-to-west and south-to-south trajectories were dominated in the west part.

A combined index to characterize agricultural drought in Italy at municipality scale

Study regionItaly and in particular the provinces of Verona and Foggia. Study focusThe assessment of drought impacts at local scale requires adequately detailed spatio-temporal estimates of drought severity. Given the intrinsic uncertainty in drought severity estimates based on a single index, especially at high spatial resolution, the use of combined indices is preferable. However, the disagreement between the single indices needs to be addressed. We propose a methodology to combine the Standardized Precipitation-Evapotranspiration Index and the Soil Moisture Anomalies based on a double-entry matrix. The classification adopted to define five semi-quantitative severity classes is generalized by introducing an objective approach to assign values when the two base indices disagree. The methodology is tuned over two Italian provinces, Verona and Foggia, with focus on agricultural drought at the high spatial detail of single municipalities. New hydrological insights for the regionThe methodology is proved to be skillful (Heidke Skill Score of 0.75) in capturing the spatio-temporal evolution of the major agricultural droughts observed in the two case study regions (2012, 2015 and 2017), which are benchmarked using data from drought impact databases. The temporal dynamics modeled by this index align with the timeline of the drought events, suggesting that the index is suitable for near-real time agricultural drought monitoring. The simplicity of the double-entry matrix approach allows for upscaling to the entire country.

Drought in Shanxi Province Based on Remote Sensing Drought Index Analysis of Spatial and Temporal Variation Characteristics

Drought is a natural disaster with long duration and which causes great harm. Studying the characteristics of drought evolution in Shanxi Province can grasp the regularity of drought occurrence and provide a basis for drought prevention and resistance. This study utilizes MODIS products to analyze and quantify the extent of drought in a specific area. The study calculates several indices, including the Crop Water Stress Index (CWSI), Vegetation Supply Water Index (VSWI), and Temperature Vegetation Dryness Index (TVDI), using variables such as the Normalized Difference Vegetation Index (NDVI), Land Surface Temperature (LST), Evapotranspiration (ET), and Potential Evapotranspiration (PET). Additionally, three drought indices are analyzed for correlation with the self-calibrated Palmer Drought Severity Index (sc-PDSI), and the most suitable drought index is selected through validation with typical drought events. Finally, the selected indices are used to investigate the spatiotemporal characteristics of drought in the study area from 2001 to 2020. The results show: (1) CWSI and sc-PDSI have a strong correlation both in terms of time and spatial analysis. Furthermore, CWSI has been shown to be more effective in monitoring significant drought events. (2) The multi-year mean values of CWSI range from 0.71 to 0.85, with a significant degree of spatial heterogeneity. In the study area, the percentage of the area affected by different levels of drought is in the following order: moderate drought > severe drought > mild drought > no drought. (3) The trend of CWSI changes shows that the drought situation in Shanxi Province has been alleviated from 2001 to 2020, and the overall spatial distribution indicates that the degree of drought alleviation in the southern region is greater than that in the northern region. The turning point from drought to wetness in the study area was in 2011, showing the overall characteristic of “dry in the north and wet in the south”.

Analysis of the Variability Characteristics and Applicability of SPEI in Mainland China from 1985 to 2018

Drought is one of the most destructive natural disasters in China and can cause serious environmental and socio-economic impacts. Based on monthly precipitation and temperature data from 571 meteorological stations, the Standardized Precipitation Evapotranspiration Index (SPEI) was calculated on a 12-month scale (SPEI-12) from 1985 to 2018 in mainland China, and it was compared with the records of the Bulletin of Flood and Drought Disasters in China to verify its drought monitoring accuracy. Then, run theory was used to explore in depth the spatiotemporal distribution of drought characteristics and trends in various climatic sub-regions. The results showed that: (1) the comparison with the Bulletin of Flood and Drought Disasters in China indicated that the results of SPEI-12 monitoring drought had high accuracy and could identify drought events in mainland China. (2) About 70% of the regions in mainland China experienced droughts more than 50 times, and about 43% of the regions had drought durations of between 100 and 110 months. Nearly 11% of the regions had drought severities of more than 130, which were mainly located in the Northwest Desert (NWC), the southern part of Northeast China (NEC), and the western part of North China (NC). (3) In the past 34 years, the droughts in the Northwest Desert (NWC), the western part of Inner Mongolia (IM), and the Qinghai-Tibet Plateau (TP) showed an aridity trend, while the droughts in South China (SC) and eastern Central and South China (CSC) presented a mitigation tendency. (4) Specifically, the droughts in South China (SC) were more influenced by precipitation, while those in the Northwest Desert (NWC) and Northeast China (NEC) were influenced by temperature and potential evapotranspiration, and the evolution of drought in North China (NC) and the Qinghai-Tibet Plateau (TP) was mainly influenced by soil moisture. The study could provide scientific guidance and a reference for drought response and sustainable development in China.

Identifying spatiotemporal propagation of droughts in the agro-pastoral ecotone of northern China with long-term WRF simulations

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.

Integrating multiple comparison methods for attributing hydrological drought evolution and drought propagation: The impact of climate change cannot be ignored

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 (PTS), peak point (PTP), and end point (PTE); (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.

Construction of a Time-Variant Integrated Drought Index Based on the GAMLSS Approach and Copula Function

Construction of an integrated drought index is a fundamental task to conducting drought disaster risk management and developing drought resistance planning strategies. Given the evident non-consistent features during the drought evolution process, firstly, the GAMLSS approach was utilized to construct multiple combination scenarios of time-variant parameters and corresponding probability distribution functions. Then, the time-variant comprehensive drought index integrating the variable characteristics of precipitation and soil moisture was established by means of the copula function. Finally, the reliability of the time-variant comprehensive drought index was verified through its application in frequency analysis and return period determination of drought hazard system in Huaibei Plain, China. The application results demonstrated that: (1) The variation of the time-variant integrated drought indicator presented strong consistency with both soil moisture and precipitation during historical years in Huaibei Plain. (2) The overall variation of the drought hazard system characterized by drought duration and severity presented a gradual mitigation trend from west to east and north to south in Huaibei Plain, which agrees with the geographic differences and water resources availability distribution features. (3) Drought recognition results, including the frequency of drought events and typical drought processes with extreme grades, are in agreement with the practical statistics and observed data series. On the whole, the proposed time-variant integrated drought indicator is capable of extracting complex variation characteristics within the drought hazard evolution process, and can be further applied in drought monitoring, recognition and assessment research fields.

The future of Iberian droughts: a deeper analysis based on multi-scenario and a multi-model ensemble approach

As a result of warming and precipitation deficits, the increasing shortage of water resources, droughts have become one of the main drivers of desertification, land degradation and food insecurity with direct impacts on ecosystems and society, especially in fragile communities. Over the Iberian Peninsula, a known climate change hotspot, the occurrence of droughts varies in intensity and severity, being its assessment under present and future conditions an important tool for adaptation measures. Here, for the first time, we present a comprehensive analysis of different plausible evolutions of droughts throughout the twenty-first century over Iberia on a monthly basis, featuring three different emission scenarios (RCP2.6, RCP4.5, RCP8.5). A multi-variable, multi-model EURO-CORDEX weighted ensemble is used to assess future drought conditions using the SPI (Standardized Precipitation Index) and SPEI (Standardized Precipitation Evapotranspiration Index). All indexes were computed by considering the full period, from 1971 to 2000 merged with 2011–2100 from each RCP scenario. The results clearly show that the Iberian Peninsula is highly vulnerable to climate change, indicating a significant increase in the intensity and severity of drought occurrences, even for the low-end RCP2.6 scenario. For the RCP4.5 and RCP8.5 scenarios, the increases are more pronounced and enhanced throughout the twenty-first century, from 3 up to 12 more severe droughts for the shorter timescales with increases in mean duration above 30 months for the longer accumulation periods. The use of all the RCPs data pooled together with a multi-variable weighted ensemble approach allows not only a more accurate and robust projection of future droughts but also ensures comparability among the projections from the three RCP scenarios. The future drought evolution aspires to assist the new Portuguese national roadmap for adaptation for the twenty-first century, bridging the water sector challenges from mitigation to adaptation in a dynamic way.

Reconstructing a long-term water storage-based drought index in the Yangtze River Basin

Drought is a prolonged dry period in the natural climate cycle, and is one of the most costly weather events. The Gravity Recovery and Climate Experiment (GRACE) derived terrestrial water storage anomalies (TWSA) have been widely used to assess drought severity. However, the relatively short cover period of GRACE and GRACE Follow-On limit our knowledge about the characterization and evolution of drought over decades time scale. This study proposes a standardized GRACE reconstructed TWSA index (SGRTI) to assess the drought severity based on a statistical reconstruction method calibrated by GRACE observations. Results show that the SGRTI correlates well with 6-month scale SPI and SPEI, with correlation coefficients reaching 0.79 and 0.81 in the YRB from 1981 to 2019. Soil moisture can capture drought condition like the SGRTI, while cannot further reflect deeper water storage depletion. The SGRTI is also comparable to the SRI and in-situ water level. As a case study for the Yangtze River Basin, its three sub-basins experience more frequent droughts, shorter drought duration, and lower severity drought, as identified by SGRTI during 1992–2019 relative to 1963–1991. The presented SGRTI in this study can provide a valuable supplement to the drought index before the GRACE era.

Dynamic evolution of recent droughts in Central Asia based on microwave remote sensing satellite products

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.

Spatiotemporal Features and Time-Lagged Effects of Drought on Terrestrial Ecosystem in Southwest China

With global warming, the increase in the frequency and intensity of droughts have severely affected the balance of terrestrial ecosystems. Although the immediate effects of drought on vegetation growth have been widely studied, the time-lagged effects have been neglected, particularly in ecologically fragile karst areas. We examined the vegetation growth trends and abrupt changes in southwest China from 1990 to 2018 by reconstructing the normalized difference vegetation index (NDVI); we then used the standardized precipitation and evapotranspiration index (SPEI) to explore the drought evolution characteristics and the time-lagged effect of drought on vegetation growth. The results showed that 97% of the study area exhibited a greening trend, which accelerated after 1995. Spring drought increased noticeably. We demonstrated that drought had a time-lagged effect on vegetation growth; 27.28% of the vegetation lands had a lag time of less than 3 months, and the mean lagged time in karst areas was shorter than that in non-karst areas. Compared to other vegetation types, the cultivated vegetation had weaker drought resistance, while the mixed-forest had stronger tolerance to drought. This study contributes to a further understanding of the drought–vegetation relationship and has important implications for optimizing vegetation conservation strategies in southwest China while coping with climate change.

The Forest Resistance to Droughts Differentiated by Tree Height in Central Europe

AbstractMore frequent droughts are altering the dynamics and function of the European forest ecosystem, which is deeply connected to the global carbon cycle. Tree height is an important structural feature of forests; however, how it regulates the response of forests to droughts remains controversial. By comprehensively examining the variations of satellite‐based vegetation greenness with drought evolution and the legacy effect of drought indicated by radial growth, we observed apparent height‐dependence forests' resistance to drought. Short forests showed lower resistance to drought than taller forests, demonstrating earlier and larger negative vegetation greenness anomalies. Additionally, larger reductions in radial growth after the drought year were also observed for shorter trees, implying an apparent legacy effect of drought on tree growth. The observed resistance differences can be attributed to the differences in the capacity for water absorption and regulation among forests of different heights. Our results provide an integrated explanation of tree‐level function that will be critical in understanding the response of forests and vegetation‐climate feedbacks in more widespread, prolonged, and extreme drought in the future.

Using the Global Navigation Satellite System and Precipitation Data to Establish the Propagation Characteristics of Meteorological and Hydrological Drought in Yunnan, China

AbstractAnalyzing the spatiotemporal characteristics and evolution of meteorological and hydrological droughts can reproduce the process of drought propagation, which helps reduce the impact of droughts and improve water resources management. While emerging studies have attempted to build drought severity index based on the cutting‐edge space geodetic observations, few have focused the propagation characteristics of meteorological to hydrological drought using geodetic data. In this paper, using global navigation satellite systems (GNSS) observations together with precipitation data, we systematically investigated drought propagation in the Yunnan province, Southwest China. We first identified seven meteorological and seven hydrological droughts in Yunnan from January 2011 to May 2021, and the meteorological drought was mainly concentrated in northern Yunnan lasting for 1–11 months. By contrast, hydrological droughts were more severe and larger than meteorological droughts, lasting for 2–16 months. The drought propagation time was 2–7 months, short in the southwest but long in the northeast. Water vapor, precipitation, and water storage demonstrated a spatiotemporal pattern of uneven distribution, with the red river fault (RRF) as the boundary, and their phase difference also presented notable regional differences, indicating that the RRF not only influences spatial variation of water resources but also affects drought propagation.

High resolution monitoring and probabilistic prediction of meteorological drought in a Mediterranean environment

Drought remains a costly natural disaster, with strong socio-economic and environmental impacts. Skilful seasonal drought forecasts can help to make early decisions. Here we assess the quality of a prototype seasonal forecasting system for a Mediterranean region (peninsular Spain + Balearic Islands) to predict meteorological drought as measured by the standardised precipitation index (SPI). We first show that there is a high agreement between the official data provided by the Spanish Meteorological Agency and the state-of-the art ERA5 reanalysis, building confidence in using these datasets. Thus, since the ERA5 data are provided in near-real time as it is updated on a monthly basis, it can be used to monitor drought evolution. Then, we demonstrate that it is possible to obtain skilful and reliable seasonal drought predictions several months in advance by applying an ensemble-based streamflow prediction system (ESP, an ensemble based on the rearrangement of historical data) using ERA5 data as initial conditions. The results indicate that a statistical persistence-based model could lead to an actionable seasonal drought forecasting skill thus providing the basis for a cheap and fast prototype for drought early warning.

Spatiotemporal Evolution and Hysteresis Analysis of Drought Based on Rainfed-Irrigated Arable Land

Drought poses a serious threat to agricultural production and food security in the context of global climate change. Few studies have explored the response mechanism and lag time of agricultural drought to meteorological drought from the perspective of cultivated land types. This paper analyzes the spatiotemporal evolution patterns and hysteresis relationship of meteorological and agricultural droughts in the middle and lower reaches of the Yangtze River in China. Here, the Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation index products and surface temperature products were selected to calculate the Temperature Vegetation Dryness Index (TVDI) from 2010 to 2015. Furthermore, we obtained the Standardized Precipitation Evapotranspiration Index (SPEI) and the Palmer Drought Severity Index (PDSI) for the same period. Based on these indices, we analyzed the correlation and the hysteresis relationship between agricultural and meteorological drought in rainfed and irrigated arable land. The results showed that, (1) compared with SPEI, the high spatial resolution PDSI data were deemed more suitable for the subsequent accurate and scientific analysis of the relationship between meteorological and agricultural droughts. (2) When meteorological drought occurs, irrigated arable land is the first to experience agricultural drought, and then alleviates when the drought is most severe in rainfed arable land, indicating that irrigated arable land is more sensitive to drought events when exposed to the same degree of drought risk. However, rainfed arable land is actually more susceptible to agricultural drought due to the intervention of irrigation measures. (3) According to the cross-wavelet transform analysis, agricultural droughts significantly lag behind meteorological droughts by about 33 days during the development process of drought events. (4) The spatial distribution of the correlation coefficient between the PDSI and TVDI shows that the area with negative correlations of rainfed croplands and the area with positive correlations of irrigated croplands account for 77.55% and 68.04% of cropland areas, respectively. This study clarifies and distinguishes the details of the meteorological-to-agricultural drought relationship in rainfed and irrigated arable land, noting that an accurate lag time can provide useful guidance for drought monitoring management and irrigation project planning in the middle and lower reaches of the Yangtze River.

The spatiotemporal evolution of socioeconomic drought in the Arid Area of Northwest China based on the Water Poverty Index

The Arid Area of Northwest China (AANC) has the most resource-based water scarcity in China. It also has engineering-, structural-, and management-based water scarcity, all of which seriously restricts the AANC's socioeconomic development. This paper uses the Water Poverty Index's (WPI) characterization of socioeconomic drought to analyze WPI change trends and spatiotemporal patterns in the AANC from 2001 to 2020. Further, the paper comprehensively analyzes the relative water scarcity degree across different zones, using the Structural Equation Model (SEM) to identify the main factors affecting the WPI and the contribution rate of each factor. The results show that the average value of the WPI in the AANC from 2001 to 2020 was 45.6, indicating severe drought. However, from 2016 onward, the degree of socioeconomic drought eased and then transitioned to moderate drought. Significant differences in the spatial distribution of the WPI occur in the AANC, with the WPI in the Hexi Corridor (47.17) being higher than the regional average (45.32), the WPI in northern Xinjiang (45.74) being the same as the regional average, and the WPI in southern Xinjiang (43.05) being lower. There are different types of water scarcity problems across the region, with Alashan, Kezhou and Zhangye experiencing water scarcity that is resource-, engineering-, and management-based, respectively. Numerous factors affect the socioeconomic drought in the AANC. Potential water resources are the main factor, with a contribution rate of 36.58%. Water supply facilities, utilization capacity, use efficiency, and the environment have a relatively small impact on the WPI, with contribution rates of 18.29%, 15.36%, 15.52%, and 14.25%, respectively. This study can provide a reference framework for the construction of a regional socioeconomic index system for drought evaluation. It can also provide scientific and technological support for regional water resources management and industrial structure planning.

Spatio-Temporal Evolution and Propagation of Meteoro-Hydrological Drought in Yalong River Basin

Based on the meteorological and hydrological data of the Yalong River Basin from 1960 to 2019, meteorological and hydrological droughts were analyzed using the standardized precipitation evapotranspiration index (SPEI) and standardized runoff index (SRI); then, the spatio-temporal evolution and propagation characteristics of the droughts were studied on multiple time scales. The results showed that, firstly, on the annual scale, the frequencies of meteorological and hydrological droughts in the basin were 28.3% and 34.0%, respectively, in the past 60 years. From upstream to downstream, the longer the alternating period of dry and wet periods, the more significant the frequency of droughts. Secondly, on a seasonal scale, the frequency of meteorological droughts is high in autumn, and the frequency of hydrological drought is high in autumn and winter. The frequency of drought in different seasons decreases from the upper reaches to the lower reaches of the basin. Thirdly, on a monthly scale, the severe and exceptional meteorological drought frequencies are high from March to May, and the severe and exceptional hydrological drought frequencies are high in January, March, October, and December. The frequency of hydrological droughts is much higher than that of meteorological droughts, especially with respect to severe and exceptional drought. Meteorological and hydrological droughts spread in the same period without lag, but they tend to expand. The propagation time of drought is short in summer and autumn, but long in spring and winter. The conclusions can serve as a decision-making basis for the water diversion planning of the west route of China’s South-to-North Water Diversion Project and the cascade hydropower operation of the basin.

Higher atmospheric evapotranspiration demand intensified drought in semi‐arid sandy lands, northern China

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

A new integrated index for drought stress monitoring based on decomposed vegetation response factors

Drought is a complex process that usually stems from aberrant climatic conditions such as precipitation deficits and temperature anomalies. Drought can pose a serious threat to vegetation growth, which in turn regulates the process of drought evolution. An in-depth understanding of the interaction between drought and vegetation is crucial not only for drought monitoring but also for drought mitigation. To this end, this study divided the drought process into two sub-processes: (1) from physical dry conditions to drought stress and (2) from drought stress to vegetation destruction, and introduced vegetation response factors to quantitatively depict the vegetation contributions in each sub-process. Response factors of different vegetation types were decomposed respectively from Temperature Condition Index (TCI), Soil Moisture Condition Index (SMCI), and Precipitation Condition Index (PCI) in the first sub-process, and from Vegetation Condition Index (VCI) in the second sub-process. Further, this study proposed a novel integrated drought index named Type Response-Aided Drought Index (TRADI) based on the response factors of different vegetation types. Vegetation response factors were applied to fine-tune several commonly used single drought indices to verify their effectiveness and the proposed TRADI was evaluated by comparing it with several combined indices, including Vegetation Health Index (VHI), Scaled Drought Condition Index (SDCI), Microwave Integrated Drought Index (MIDI), and Integrated Drought Monitoring Index (IDMI). Moreover, the TRADI was qualitatively evaluated with the maps from U.S. Drought Monitor (USDM) in the 2011 and 2012 drought events across the CONtinental United States (CONUS). Our results showed that adjusted by vegetation response factors, single drought indices as well as combined drought indices showed a closer correlation with the Palmer Drought Severity Index (PDSI) than their original forms, indicating the strength of response factors in modifying existing indices. Furthermore, the proposed TRADI performed better than VHI, SDCI, MIDI, and IDMI, and was consistent with USDM in typical drought events. This study provides a new perspective on understanding the process of drought affecting vegetation and highlights the importance of considering vegetation response in drought index establishment.