As a key component of the water cycle, evapotranspiration (ET) not only directly affects soil moisture, river runoff, and groundwater recharge, but also plays an important role in the formation and evolution of droughts. Against the background of global warming, accurately projecting ET changes is of great significance for understanding the mechanisms of regional drought occurrence and enhancing drought resilience. Based on ET, mean temperature, and precipitation data from multiple models of the Coupled Model Intercomparison Project Phase 6 (CMIP6), this study projects the variation trends of ET and its influencing factors in the arid-prone belt of northern China under three future emission scenarios (SSP1-2.6, SSP2-4.5, and SSP5-8.5). The results show that ET exhibits a significant increasing trend under all three emission scenarios, with trend rates of 1.6, 2.0, and 3.7 mm (10 a)-1, respectively. The variation trend of ET shows a significant response to greenhouse gas emission levels, with higher emission intensities leading to more pronounced increases in ET. ET reaches its intra?annual maximum in summer, followed by spring and autumn, and is at its minimum in winter. The precipitation increase is most obvious in spring, and this contributes substantially to the ET increment. Under different emission scenarios, temperature is the dominant driving factor for ET variations, while precipitation plays a secondary regulatory role. The driving intensity of hydrothermal factors increases with rising emission levels. Precipitation constraint on ET weakens during part of summer, and ET in winter and spring is more sensitive to temperature.
Revealing the temporal and spatial evolution patterns of drought during different growth stages of mulberry trees in Guangxi has practical significance for guiding drought-resistant cultivation and ensuring the security of the industry. Daily temperature and precipitation datasets covering Guangxi from 1961 to 2025 were utilized in this study, and the Standardized Precipitation Evapotranspiration Index (SPEI) was selected as the drought evaluation indicator, to investigate the spatiotemporal drought characteristics in different growth stages of mulberry in Guangxi using linear trend analysis, wavelet analysis and spatial interpolation methods. The main results are summarized as follows: (1) Interannual fluctuations were identified as the dominant variation characteristics of SPEI for all mulberry growth stages during 1961-2025, and no significant linear trends were detected. The significant short cycles of 2-4 years were captured during the germination and leaf expansion stages, and the significant short cycles of 3-4 years and 7 years were observed during the vigorous growth stage, the significant short cycles of 3 years and 5-6 years were found during the defoliation and dormancy stage. None of the global dominant cycles of each growth stage passed the significance test at the 0.05 level, which indicated that the drought evolution was dominated by significant short-period oscillations. (2) Light drought was verified as the primary drought type restricting mulberry production at all growth stages in Guangxi. The occurrence frequencies of moderate, severe and extreme drought decreased successively. The highest drought frequency was detected during the germination stage, with widespread light drought across the whole study area. Northwestern Guangxi was identified as the core high-frequency zone of light drought, and moderate drought presented a zonal high-value pattern across the central Guangxi. High-frequency areas of light drought were mainly distributed in eastern and western Guangxi during the leaf expansion stage, while high-incidence regions of moderate drought were shifted to northern, central and southeastern Guangxi. The maximum water consumption was required for mulberry during the vigorous growth stage, yet the spatial distribution of drought was relatively uniform, and local severe drought with certain frequencies was only prone to occur in central and eastern Guangxi. High-incidence zones of light drought were concentrated in central and eastern Guangxi during the defoliation and dormancy stage, and moderate drought exhibited an obvious spatial pattern with higher frequency in western Guangxi and lower frequency in eastern Guangxi.
Clarifying the spatial-temporal differentiation of drought in the Hexi Corridor and its surrounding regions can provide a scientific support basis for regional drought prevention and disaster reduction, sustainable management of oasis agriculture, and the maintenance of ecological security barriers. In this study, the Hexi Corridor and its surrounding areas were divided into three sub-regions: the northwestern Hexi region, the eastern Hexi region, and the Qilian Mountains. Monthly observation data from 17 meteorological stations during 1961-2020 were used. The Standardized Precipitation-Evapotranspiration Index (SPEI) was adopted as the drought indicator. Methods including the Mann-Kendall mutation test, run-length theory and spatial interpolation were employed to analyze regional climate fluctuation characteristics and the spatial-temporal evolution of drought. The results show that: (1) The climate of the Hexi Corridor and its surrounding areas generally exhibits an overall warming-wetting trend. The warming rates decrease in the order of the eastern Hexi region, the Qilian Mountains and the northwestern Hexi region, with values of 0.42, 0.38 and 0.32 ℃·(10 a)-1, respectively. Precipitation in the Qilian Mountains increases significantly at a rate of 9.1 mm·(10 a)-1 (p<0.05), whereas only slight increasing trends are observed in the other regions. (2) Multi-timescale drought analysis indicates that drought in the northwestern Hexi Corridor is characterized by a short-term response, whereas the Qilian Mountains and the eastern Hexi Corridor exhibit a cumulative response. Drought intensity across the study area exhibits an evolutionary feature of “the widespread occurrence of mild drought, the expansion of moderate drought, and the emergence of extreme drought”. Since the beginning of the 21st century, the frequencies of moderate and extreme drought events have increased markedly. (3) Significant spatial differences are observed among drought severity levels. The northwestern Hexi Corridor is dominated by mild drought over the long term,with relatively stable drought condition. The occurrence frequencies of severe and extreme drought increase obviously in the eastern Hexi Corridor and the Qilian Mountains. Drought characteristics in the Qilian Mountains shift from increasing occurrence frequency to intensifying severity, posing a growing threat to the regional water conservation function.
In midsummer 2022, the southern Sichuan Basin (hereinafter referred to as Southern Sichuan) experienced the most severe high-temperature and drought event since meteorological records began in 1961, causing serious impacts on local agricultural production, particularly the ratooning rice industry. To reveal the regional characteristics of this extreme high-temperature and drought event and its potential impacts on ratooning rice production, this study analyzed the spatiotemporal evolution characteristics and extremity of high temperatures in midsummer 2022 based on data from 22 national meteorological observation stations in Southern Sichuan, evaluated the spatiotemporal dynamic changes of drought using the Meteorological Drought Composite Index (MCI), quantified the number of compound stress days combining high temperature and drought, and further investigated the causes of the extreme high temperatures from the perspectives of atmospheric circulation anomalies and land-atmosphere feedback effects using ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts. The results show that: (1) The regional average temperature in Southern Sichuan in midsummer 2022 was 31.9 ℃, 4.6 ℃ above the climatological mean, making it the highest on record for the same period. The regional average precipitation was only 101.4 mm, 69% less than the climatological mean, also the lowest on record for the same period. (2) The high-temperature event comprised two episodes: the first lasted 12 days and the second lasted 35 days, both covering the entire region. The number of days with temperatures exceeding 40 ℃ ranged from 6 to 31 days, with the longest duration (31 days) recorded at Hejiang. Among the 22 stations, 18 broke their historical maximum temperature records, with the highest value of 44.3 ℃ observed at Xuyong. The daily duration of high temperatures increased significantly, reaching up to 20 hours at some stations. Drought began in early July and peaked in late August, with Longchang experiencing the most severe conditions (53 days of severe drought and 10 days of extreme drought). During the second high-temperature episode, the average number of compound stress days (daily maximum temperature ≥35 ℃ combined with moderate drought or above) was 20 days, and the compound stress days was more than 33 d at stations such as Longchang and Gulin, indicating that the eastern and northern parts of the region are high-risk areas for compound stress on ratooning rice. (3) The western Pacific subtropical high area index anomaly reached 0.15×105 km2, which was the highest since 1990, and Southern Sichuan was controlled by persistent subsiding airflow with enhanced clear-sky radiation. Soil moisture anomaly dropped to its lowest value (-0.08 m3·m-3), while surface sensible heat flux anomaly rose to its highest value of 12.15 W·m-2, forming a positive “high temperature-drought” feedback mechanism that simultaneously amplified both the high-temperature and the drought.
Drought is one of the major natural hazards worldwide, severely impacting ecosystems and agricultural production. The southwestern region of China has complex terrain and variable climate, and drought poses an especially significant threat to the vegetation ecosystem. This study characterized drought processes using multi-scale Standardized Precipitation Evapotranspiration Index (SPEI) and monitored vegetation growth with Kernel Normalized Difference Vegetation Index (kNDVI) and Enhanced Vegetation Index (EVI) derived from MODIS imagery. The kNDVI, based on kernel methods, effectively mitigates the saturation problem of traditional Normalized Difference Vegetation Index (NDVI) in high-cover areas, enhancing sensitivity and noise resistance in dense vegetation environments. Together with EVI, it provides more robust monitoring of vegetation responses. Pixel-scale correlation analysis was employed to reveal the relationship between drought and vegetation, and run theory and multiple linear regression were applied to systematically analyze the duration, severity, and intensity of drought events from 2001 to 2022, and assessed vegetation change trends, further elucidated the cumulative impacts of drought on vegetation. The results indicate that: 1) Drought in southwest China exhibits significant spatial heterogeneity, with high frequency, long duration, and high intensity in northeastern Yunnan and the Sichuan Basin, and notable drought risks in the Hengduan Mountains and the Zoige Plateau, while the Yunnan-Guizhou Plateau and Guangxi Hills experience relatively low drought risk. 2) Drought characteristics vary with time scales: short-term drought (SPEI-1) affects a wide area but with short duration and low severity. In contrast, medium- to long-term droughts (SPEI-6 and SPEI-12) display stronger cumulative effects, with significantly increased duration and intensity, exerting more persistent impacts on vegetation. 3) Vegetation response to drought shows clear spatiotemporal heterogeneity. Both kNDVI and EVI reveal that vegetation growth is predominantly influenced by the cumulative effects of medium-short-term (3, 6 months) droughts, with approximately 50% of the vegetation area being most sensitive to this time scale. The high consistency of the two indices strengthens the robustness of the findings, while their local sensitivity differences help uncover the multi-path response mechanisms of vegetation from short-term physiological stress to long-term biomass accumulation.
Drought is one of the most prominent natural disasters in the Loess Plateau. Its spatiotemporal evolution has direct effects on the stability of regional ecosystems, the security of agricultural production, and the high-quality development in the Yellow River Basin. Based on the daily observed meteorological data of 218 stations from 1961 to 2020, the reference crop evapotranspiration (ET0) was firstly calculated with the Penman-Monteith formula. Then, the daily water balance sequence was calculated based on daily precipitation and ET0. Lastly, this study calculated the 30-day sliding cumulative daily standardized precipitation evaporation index (SPEI-30). Based on SPEI-30, this study investigated the spatiotemporal evolution of droughts’ lasting days, droughts’ frequency, and the serious levels of droughts in the Loess Plateau in the last 60 years. This study also adopted random forest regression models to quantify the relative contributions of meteorological factors to the evolution of drought. The results show that the daily SPEI-30 can effectively identify the occurrence and lasting days of drought, catch droughts’ fluctuation at the 30-day scale, and reflect the dynamic evolution process of drought in the Loess Plateau. There were significant interdecadal fluctuations and seasonal differences on droughts’ lasting days and its frequency. In specific, droughts’ lasting days were relative more from 1961 to 1980 and from 2001 to 2020, but less from 1981 to 2000. The lasting days and frequency of drought in spring and winter showed a downward trend but an upward trend in summer and autumn. The effects of meteorological factors on the variation of the duration of drought were different among seasons. Precipitation was the dominated factor for spring and autumn droughts (contributions reaching 43% and 42%, respectively). Summer and winter droughts were dominated by ET0 (contributions of 36% and 30%, respectively). In summary, the spatiotemporal evolution of drought showed significant seasonal differences in the Loess Plateau, and meteorological factors were the main factors affecting the duration of regional drought.
Understanding the spatiotemporal evolution of multi-type drought and its responses to temperature and precipitation is crucial for drought risk assessment and water resources management under a warming climate. This study is based on global multi-source observational and reanalysis datasets covering the period 1982 to 2022. The Self-Calibrating Palmer Drought Severity Index (scPDSI), Standardized Soil Moisture Index (SSMI), Standardized Runoff Index (SRI) and Standardized Vegetation Health Index (SVHI) are constructed to characterize meteorological, agricultural, hydrological, and ecological droughts, respectively. Using linear trend analysis and multiple regression methods, this study investigates the long-term trends and variability of multi-type droughts across global climate zones and quantifies the contributions of temperature and precipitation to these changes. The results indicate a significant global intensification of meteorological, hydrological, and ecological droughts, whereas agricultural drought shows a contrasting hemispheric pattern, with alleviation in the Northern Hemisphere and intensification in the Southern Hemisphere. Meteorological drought variability decreased markedly, whereas the variability of agricultural, hydrological droughts generally increased. In arid regions, the responses of different drought indexes are inconsistent. The mitigation trend in agricultural drought is opposite to the aggravation trends in meteorological, hydrological, and ecological droughts. Moreover, the changes in variability of meteorological and ecological droughts are more pronounced in arid regions compared with other regions. In humid regions, multi-type droughts intensified consistently, with hydrological drought showing particularly pronounced aggravation. Temperature contributes significantly more than precipitation to multi-type droughts. Warming generally exacerbates these droughts, with its contribution being particularly pronounced for meteorological, hydrological, and ecological droughts in arid regions. By contrast, increased precipitation tends to alleviate meteorological, agricultural, and hydrological droughts.
