Hydrological Response Mechanism of Aquifer Dynamic Storage during the Dry and Wet Seasons

Streamflow recession usually exists between rainfall events, and the recession can be expressed as the power relationship between the streamflow and the recession rate. Under the assumption that groundwater drainage from the aquifer to the river channel, this method can inversely evaluate the basin-scale groundwater storage using observed streamflow. It has often been used to explore regional groundwater storage conditions and storage-discharge relationships, and even to estimate hydrogeological parameters. However, the groundwater storage generating the streamflow is only a component of the dynamic storage that includes streamflow and evapotranspiration dynamic, or other forms of mobile groundwater. In order to understand the mechanism of the aquifer dynamic storage responses under environmental changes (included climate change, human activities, etc.), this study used the analytic streamflow distribution model to optimize the estimation of recession parameters during the dry and wet seasons, and explored the parameters change over time and the relationship with seasonal evapotranspiration and basin wetness conditions. Combining the water balance methods, we also quantified the dynamic storage relevant to groundwater drainage and vegetation available water (i.e. storage insensitive to streamflow), respectively, to explore the hydrological response mechanism of aquifer dynamic storage in two seasons. The results showed that the difference in recession parameters in the dry and wet seasons is related to the basin wetness condition, and the evapotranspiration effect is relatively limited. In addition, the parameters change over time also indicated that the environmental change has gradually changed the streamflow recession mechanism. By comparing the response of dynamic storage components to rainfall events and evapotranspiration, this study also demonstrated that the variability in different forms of dynamic storages during each season, which is helpful for understanding the store and loss process of groundwater storage at the basin scale and improving the possibility for predicting the different environmental impacts on groundwater storage.