Delayed Response of Soil Moisture and Hydrological Droughts to Meteorological Drought Over East Asia

The frequency and severity of meteorological drought across Eastern Asia (EA) are observed and projected to increase with ongoing global climate change. However, the temporal and spatial responses of land surface elements including soil moisture and runoff to meteorological drought remain insufficiently understood and characterised, especially in terms of quantifying the differentiated lag time of soil moisture and hydrological drought responses. In this study, we investigate the spatiotemporal response of soil moisture and hydrological droughts to meteorological drought across EA, using the Standardised Precipitation Index (SPI; a measure of precipitation deficit), Standardised Soil Moisture Drought Index (SSMDI; quantifying soil moisture anomalies) and Standardised Streamflow Index (SSI; assessing streamflow deviations) at short- (1-3), medium- (6-9) and long-scales (12-24 months). The results show that in northern EA, soil moisture droughts indicate weak negative correlations with meteorological droughts at 1-6 month time scales, while in southern regions, stronger positive correlations are observed at 9-24 month time scales. Hydrological droughts exhibit consistently strong positive correlations with meteorological droughts across all time scales, especially in the southern regions of EA. Northern regions exhibit longer lag times of up to 8 months of soil moisture droughts in response to meteorological drought, whereas southern regions exhibit rapid responses (1 month). In all time scales, hydrological droughts in northern regions of EA have a delayed lag times extending up to 10 months. As climate change and land use changes may amplify drought impacts, long-term forecasting and adaptive management are essential to mitigate water shortages and ecological stress across the EA region.