Trigger thresholds and drivers of meteorological to agricultural drought propagation in the Hanjiang basin under climate change

Climate change is redefining meteorological triggers of agricultural drought in the upper–middle Hanjiang River Basin (UMHRB), threatening water and food security. We coupled a calibrated VIC model with bias-corrected NEX-GDDP-CMIP6 forcings to reconstruct (1980–2020) and project (2021–2100) root zone soil moisture. Copula–Bayesian conditional probability yields agricultural drought trigger thresholds (ADTTs) from mild to extreme events, while the Lindeman–Merenda–Gold (LMG) metric, proportional marginal variance decomposition (PMVD), and relative weight analysis (RWA) apportion the influence of temperature, precipitation, and evaporation. Under SSP2-4.5 and SSP5-8.5, annual and seasonal ADTTs rise basin-wide; moderate thresholds increase most – so by 2100, a one-class weaker meteorological drought (SPI-3 ≈ −1.0) can trigger agricultural drought. Converging thresholds across severity classes foreshadow more frequent, short, extreme soil-moisture deficits. Temperature dominates annual ADTT inflation, whereas precipitation and evaporation govern most seasonal responses. These dynamic, driver-specific thresholds provide actionable metrics for early warning, crop-insurance triggers, and adaptive water allocation, and the framework is transferable to other monsoon-influenced basins. The results inform management of two national inter-basin water transfer schemes traversing the UMHRB.