Unravelling the Transfer Mechanisms and Time Lags between Meteorological, Agricultural and Hydrological Droughts Varying with Aquifer Vertical Heterogeneity

Drought is a complex natural hazard that propagates through the hydrological cycle, often evolving from meteorological anomalies to agricultural water deficit and eventually hydrological stress. Understanding spatiotemporal dynamics and the propagation between these different drought types is crucial for effective water resource management, yet the quantitative characterization of the specific transition rates and time lags remains challenging, particularly when considering the vertical heterogeneity of aquifers.

This study investigates the evolution and propagation of drought in the Aa of Weerijs catchment, Netherlands, over the period 1993–2024. We employed a multi-index approach, utilizing the Standardized Precipitation (Evapotranspiration) Index (SPI/SPEI) to characterize meteorological drought, the Palmer Drought Severity Index (PDSI) as a proxy for agricultural water deficits, and the Standardized Groundwater Index (SGI) for groundwater drought at various depths, reflecting the response of different aquifer systems. By applying run theory for drought event detection and event coincidence analysis for matching different types of drought events, we quantified both the propagation time lags and transition probabilities. The lagged correlation analysis was further employed to examine the statistical relationships across varying temporal delays.

Our preliminary results reveal that, 1) Significant intensification of drought severity is observed in the recent decade for some monitoring wells; 2) Depth-dependent propagation characteristics were confirmed, with deeper monitoring points generally showing higher correlation coefficients and varied propagation rates, though not all stations exhibited a simple “deeper equals longer lag” pattern; 3) SPEI-based propagation was consistently weaker than SPI-based in both correlation and propagation rate, suggesting evapotranspiration may reduce the efficiency or detectability of meteorological drought propagation into groundwater; 4) PDSI showed the strongest coupling with SGI across nearly all stations and depths, often with the highest propagation rate.

This research highlights the critical role of aquifer depth in modulating drought propagation and emphasizes the non-linear transfer behaviours within the hydrological cycle. The findings provide scientific evidence for developing depth-specific drought early warning systems and optimizing regional water allocation strategies under a changing climate.