Three-dimensional spatio-temporal propagation dynamics from soil moisture to vegetation droughts across different eco-geographical regions of China

Abstract

Study region China. Study focus This study investigated the propagation from soil moisture drought (SD) to vegetation drought (VD) across China during 1981–2020 using a three-dimensional (3-D) spatio-temporal clustering framework. SD and VD events were identified based on the Standardized Soil Moisture Index (SSMI) and Standardized Vegetation Health Index (SVHI), respectively. A spatio-temporal matching algorithm was developed to pair SD and VD events, enabling a quantitative analysis of propagation characteristics (i.e., propagation time, rate, direction, distance, probability, and thresholds). The key contributors were identified using an integrated XGBoost-SHAP approach. New hydrological insights for the region This study identified 144 SD and 59 VD events, among which 24 were successfully matched as propagation events. The average propagation time from SD to VD was 3.76 months, exhibiting a distinct west-to-east gradient. The thresholds for triggering VD increased with drought severity, with SD duration thresholds ranging from 1 to 6 months across most regions. Regional contributors to drought propagation time varied across China: energy-related factors were primary in humid regions, precipitation (PRE) in arid zones, and temperature (TMP) and root-zone soil moisture (SMrz) in semi-arid areas. This study provides a comprehensive framework for understanding multi-dimensional drought propagation and offers scientific support for drought early warning and ecological risk management in China.