[Relationship between meteorological, soil, and hydrological drought propagation at different levels in Inner...

Understanding the meteorological-soil-hydrological drought propagation characteristics can provide technical supports for the formulation of drought mitigation measures. Taking Inner Mongolia as the research area, we utilized the ERA5-Land soil moisture and surface runoff dataset from the European Centre for Medium-Range Weather Forecasts from 1980 to 2022, coupled with observation data from 115 meteorological stations, to calculate standardized precipitation evapotranspiration index (SPEI), standardized soil moisture index (SSI), and standar-dized runoff index (SRI) at different temporal scales. Then, we used run theory, Theil-Sen median trend analysis, the Mann-Kendall test, and Pearson correlation analysis to investigate the lag effects across different types of droughts and the spatiotemporal distribution of propagation time. The results showed that over 85% of the region showed an intensifying trend for meteorological, soil, and hydrological droughts, with areas showing significant wetting covering less than 1% of the study area. Meteorological drought events were characterized by high frequency, low severity, and short duration, whereas soil drought events exhibited low frequency, high severity, and long duration. Hydrological droughts were dominated by high frequency, low severity, and short-duration events. The response between soil and hydrological drought was stronger than that between meteorological and hydrological drought, implicating that soil moisture deficit induced by soil drought was the primary trigger for hydrological drought. The propagation time for various levels of droughts was predominantly concentrated between two to six months, with higher-grade drought events showing more efficient transition and propagation. The continuity of meteo-rological, soil, and hydrological drought events in central and western Inner Mongolia and soil-hydrological drought events in eastern Inner Mongolia were relatively weak. This research would be of great significance in revealing the mechanisms of regional drought formation and constructing drought propagation models.