The Loess Plateau frequently endures droughts, and the propagation process has grown more intricate due to the interplay of climate change and human activities. This study developed the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Soil Moisture Index (SSMI) on a 3-month scale and examined the spatiotemporal characteristics and driving mechanisms of drought propagation from meteorological to agricultural drought utilizing cross-wavelet analysis, grey relational analysis, and the optimal parameter-based geographical detector (OPGD) model. The results demonstrate a substantial seasonal correlation between meteorological and agricultural droughts in spring, summer, and autumn, as evidenced by cross-wavelet coherence analysis (wavelet coherence > 0.8, p < 0.05). Lag analysis utilizing grey relational degree (>0.8) indicates that drought propagation generally manifests with a temporal delay of 1–3 months, with the shortest lag observed in spring (average 1.2 months) and the longest in winter (average 3.1 months). Distinct spatial heterogeneity is seen within geomorphological divisions: the loess wide valley hills and loess beam hills divisions exhibit the highest propagation rates (0.64 and 0.59), whereas the loess tableland and soil–stone hills divisions have lower propagation (around 0.50). The OPGD results reveal that precipitation, soil moisture, and temperature are the principal contributing factors, although their effects differ among geomorphological types. Interactions among components exhibit synergistic enhancement effects. This study improves our comprehension of seasonal and geomorphological heterogeneity in drought propagation from meteorological to agricultural droughts and provides quantitative evidence to support early drought warnings across various divisions, agricultural risk assessment, and water security strategies in the Loess Plateau.

The hydrological series in the Loess Plateau region has exhibited shifts in trend, mean, and/or variance as the environmental conditions have changed, indicating a departure from the assumption of stationarity. As the variations accumulate, the compound effects caused by the driving variables on runoff variations grow complex and interactive, posing a substantial risk to water security and the promotion of high-quality development in regions or river basins. This study focuses on the Tuwei River Basin in the Loess Plateau, which experiences significant changes in vegetation coverage and minimal human disturbance, and examines the cross-driving relationship between the runoff change and its driving variables (including hydrometeorological and environmental variables). A quantitative statistical analysis method based on the GAMLSS is then developed to estimate the interacting effects of changes in the driving variables and their contribution to runoff changes. Finally, various anticipated scenarios are used to simulate the changes in driving variables and runoff disturbances. The findings indicate the following: (1) The developed GU, LO, and NO distribution-based GAMLSSs provide a notable advantage in effectively capturing the variations in groundwater storage variables, actual evapotranspiration, and underlying surface parameters, as well as accurately estimating the impacts of other relevant variables. (2) The precipitation and groundwater storage variables showed predominantly positive contributions to the runoff change, but actual evapotranspiration had an adverse effect. The changes in underlying surface parameters, particularly since 2000, increase actual evapotranspiration, while decreasing groundwater storage, resulting in a progressive decrease in runoff as their contribution grows. (3) The scenario simulation results reveal that alterations to the underlying surface have a substantial influence on the evolution of runoff in the Tuwei River Basin. Additionally, there are cross-effects between the impact of various driving variables on runoff, potentially compounding the complexity of inconsistent changes in runoff sequences.

During severe drought conditions, water supply risks tend to be concentrated at critical water intake nodes and vulnerable river segments, while the conventional total balance method is inadequate for depicting the spatial evolution of these risks. This study developed a node-based water supply security assessment framework for the Feng River Basin, a representative watershed in the piedmont transition zone. The framework coupled SWAT-simulated runoff with a supply–demand balance model and evaluated water supply reliability at both the node and basin scales. Two scenarios were compared: an artificial water system scenario and an artificial water system with an engineering-based water resource allocation scenario. Dry (P = 75%) and extremely dry (P = 95%) conditions were considered to examine the performance of artificial regulation under drought stress. The results showed that basin-scale water supply reliability remained relatively stable, ranging from 0.833 to 0.853 under different scenarios. However, the node-scale results revealed strong spatial heterogeneity. Nodes 1 and 3 maintained full or nearly full reliability, whereas Nodes 4, 6, and 7 showed relatively low reliability and higher water shortage risk. Under the P = 75% scenario, engineering-based water resource allocation increased basin-scale reliability from 0.848 to 0.853, indicating a slight improvement in supply–demand balance. In contrast, under the P = 95% scenario, reliability decreased from 0.839 to 0.833 after introducing water resource allocation, suggesting that transfer-based interventions may have limited effectiveness when natural inflow is severely reduced. In particular, Node 7 showed a marked decline in reliability under the allocation scenario, indicating that water supply risks may be redistributed and concentrated at specific intake nodes under extreme drought conditions. The scenario comparison further indicates that water diversion strategies may produce a dual effect of local improvement and global reconfiguration. Insufficient supply intensity may result in engineering interventions that cause downstream water reduction impacts, leading to a spatial redistribution and shifting of risks rather than their systemic eradication. This study seeks to transition the evaluation paradigm from “total safety” to “node safety,” establishing a scientific foundation for enhancing the emergency response system in critical areas of the basin.