Influence of groundwater on the propagation of meteorological drought to agricultural drought during crop growth periods: A case study in Huaibei Plain

Groundwater plays a key role in regulating the transition from meteorological droughts (MD) to agricultural droughts (AD), though its specific influence during crop growth remains unclear. In this study, daily effective root zone soil moisture and annual yield for winter wheat and summer maize were simulated using Aquacrop model under four scenarios: Scenario 1 (groundwater level at 1 m depth), Scenario 2 (groundwater level at 2 m depth), Scenario 3 (groundwater level at 3 m depth), and Scenario 4 (groundwater level at 4 m depth). Based on the simulated data, the propagation probabilities, propagation times (PT), translation rates of drought events, and changes in drought characteristics under the four scenarios were calculated, revealing the specific impact of groundwater levels on the propagation from MD to AD. The results indicated that (1) the probability of drought propagation increased with either a decrease in the groundwater level or an increase in the MD severity. Notably, a decrease in groundwater level from 1 m to 2 m depth results in a substantial rise in propagation probability, with an average increase of 114.0 % and 118.9 % for winter wheat and summer maize, respectively. (2) PT was shortened by 2-4 days for each 1 m drop in the groundwater level. When the severity of MD intensified from severe to extreme, the PT was shortened by an average of 8 days and 10 days during the phenological stages of summer maize and winter wheat, respectively. Both crops exhibited shorter PTs during the emergence, grouting, and maturity stages, and longer PTs during the tillering and heading stages. (3) Overall, the decline of groundwater levels accelerates the translation rate of drought events. In addition, longer and stronger drought characteristics were observed especially at low levels of groundwater. (4) The optimal groundwater level was found to be about 1 m and 2 m for winter wheat and summer maize in the Huaibei Plain, respectively. These findings provide valuable insights for enhancing drought resilience and optimizing irrigation and groundwater management in the Huaibei Plain.