GRACE-based dynamic assessment of hydrological drought trigger thresholds induced by meteorological drought and possible driving mechanisms

Determining the threshold at which meteorological drought triggers hydrological drought is critical for early warning and proper mitigation of drought. However, drought trigger thresholds are difficult to determine owing to the nonlinearity between meteorological and hydrological drought, and their dynamics have not been explored. To this end, we introduce a precipitation-driven drought trigger threshold framework. This framework considers the multiscale characteristics of cumulative precipitation anomalies and incorporates the drought severity index of terrestrial water storage anomalies to characterize hydrological drought. The dynamics of trigger thresholds over time and the main drivers of these variations are further explored over China. The results show that hydrological drought is more sensitive to meteorological drought in south China, with some regions showing weak or negative correlations mainly determined by the differences between climate change and human activities. The risk of drought outbreak in the central, northeastern and southern regions of China is high, with trigger thresholds showing a dynamic decreasing trend over time (corresponding to lower cumulative precipitation anomalies), indicating weakened resistance to meteorological drought. Rising temperature is the main factor affecting dynamic changes in the trigger threshold. The drought trigger threshold framework proposed in this study is also applicable for assessments in other regions around the world. This study provides valuable insights and new approaches for understanding the mechanisms of hydrological drought formation. Furthermore, these results are expected to severe as a scientific basis for government departments to reduce water supply stress on human and natural systems and to develop adaptive management strategies.