Shanshui Yuan

Although soil moisture-atmosphere feedback (SAF) has been widely recognized as a key driver of temperature extremes, its distinct impacts on dry and humid heatwaves remain insufficiently understood, largely due to previous studies focusing predominantly on dry heatwaves alone. In this study, we combine SAF perturbation experiments from CMIP6 with partial differential analysis to construct a global map of SAF’s influence on both humid and dry heatwaves during 1985-2014 and to elucidate the underlying mechanisms. Unlike the homogeneously amplifying effect of SAF on dry heatwaves, SAF reduces the duration and severity of humid heatwaves by 20-40% in low-to-mid latitude regions with strong soil moisture-atmosphere coupling. In contrast, it increases their duration and severity by ≥50% in high latitude regions. These spatially divergent responses are primarily attributed to the competition between SAF-induced thermal warming and moisture depletion, which respectively raise or lower wet-bulb temperatures. Our findings reveal a dual regulatory mechanism by which SAF influences heat extremes through temperature-humidity coupling, providing scientific insights for region-specific adaptation strategies to both dry and humid heatwaves.

Drought–flood abrupt alternation (DFAA) events, characterized by their complex compound nature and profound impacts on ecosystems and human societies, have emerged as critical hydrometeorological risks in the middle and lower reaches of the Yangtze River basin (MLYRB), China. The concentrated and unstable characteristics of precipitation during the mei-yu season provide a typical climatic background for DFAA events. By using satellite precipitation data from 2001 to 2023, this study analyzes the spatiotemporal characteristics of DFAA occurrences and investigates how rain belt migration and mei-yu anomalies influence DFAA formation and regional differentiation. Results show that over 40% of annual DFAA events are concentrated in summer, mainly in eastern subregions with high precipitation variability. During the mei-yu season, northward migration of the rain belt reshapes the precipitation distribution and produces a distinct north–south opposition, with flood-to-drought (FTD) transitions prevailing in the south and drought-to-flood (DTF) events dominating the north. The average DFAA-affected area reaches 19.5% of the basin, with nearly equal shares of the two alternation types. Mechanistically, DFAA events are generally found to follow a chain-driven process initiated by anomalies of the western Pacific subtropical high (WPSH), which restructure moisture transport pathways and rain belt position, then lead to regional drought and flood anomalies, and finally trigger DFAA events. Meanwhile, a weakened South China Sea summer monsoon (SCSM) further enhances the north–south opposition. This study highlights the critical role of the rain belt movement and mei-yu variability in shaping DFAA patterns and provides insight into their physical drivers and regional differentiation. Significance Statement: Drought–flood abrupt alternation (DFAA) events in the middle and lower Yangtze River basin pose significant challenges for regional water management and disaster preparedness. This study clarifies the spatiotemporal distribution of these events and examines how monsoons, moisture transport, and the western Pacific subtropical high (WPSH) interact during the mei-yu season to shift the rain belt and lead to sudden hydroclimatic extremes. By uncovering how these factors combine to drive severe DFAA events, this work enhances understanding of compound hydrometeorological hazards and provides insights to support early warning systems and climate resilience planning across East Asia and other monsoon-affected regions worldwide.

Soil moisture (SM) plays a crucial role in the hydrological and ecological processes of the Yellow River Basin (YRB), with its spatiotemporal distribution and variability serving as key factors for understanding ecosystem responses to environmental changes. However, previous research has often overlooked the spatiotemporal variation of SM across different soil layers and the complex bidirectional interactions between SM and vegetation, particularly as indicated by the Normalized Difference Vegetation Index (NDVI), within different vegetation zones and soil layers. Widely used in fields such as agriculture and water cycle research, the GLDAS dataset has been applied to analyze the spatiotemporal patterns of SM at four different depths (0–10 cm, 10–40 cm, 40–100 cm, and 100–200 cm) in the YRB from 1948 to 2022, revealing a continuous increase in SM over time, with more pronounced changes after identified breakpoints (1985 for the 10–40 cm layer, and 1986 for the other layers). Granger causality tests show that the bidirectional interaction between NDVI and SM dominates across all soil layers and regions, far surpassing the unidirectional effects of SM on NDVI or vice versa. Regardless of whether SM or NDVI is the primary variable, the Temperate Evergreen Broadleaf Forest (TEBF) region consistently exhibits the strongest lag effects across all layers, followed by the Qinghai-Tibet Plateau Alpine Vegetation (QTPAV) and the Temperate Desert Region (TDR). The Subtropical Warm Temperate Deciduous Forest (SWTDF) and Temperate Grassland Region (TGR) show the weakest lag effects. This research offers new insights into the mutual feedback between vegetation and hydrology in the YRB and provides a scientific basis for more effective water resource management.

The intensification of global climate change and human activities has made drought one of the most severe global challenges, bringing unprecedented challenges to the hydrological and water resource system. Although several studies have been conducted on hydrological droughts, few have examined the response relationship between hydrological droughts and water and energy balance. This study uses multi-year drought detection and the Budyko framework to investigate the impact of climate change and human activities on runoff changes, with a focus on the differences between drought and non-drought conditions. The results indicate that (1) the sensitivity of runoff to precipitation (εPR), potential evapotranspiration (PET) (εPET), and the watershed characteristic parameter n (εn) varies over time, initially increasing and then decreasing, and peaking between 1995 and 2006. Runoff is most sensitive to precipitation (PR) and least sensitive to potential evapotranspiration (PET). (2) The dominant contribution shifted from climate change during 1977–1985 to human activities during 1986–2014. (3) Multi-year drought in the Yellow River Basin (YRB) significantly altered n, εPR, εPET, and εn, changing from (1.50, 2.19, −1.19, −5.66) in non-drought periods to (1.84, 2.57, −1.57, −9.93) in drought periods, with greater absolute values during drought periods. (4) Compared to non-drought periods, the contribution scores of human activities (δh) are significantly higher. The growing contribution of human activities to runoff can exacerbate the occurrence of hydrological droughts.