Artificial groundwater recharge for adapting to drought risk in large agricultural areas

Artificial groundwater recharge is a promising adaptation measure to face the increasing drought risk on freshwater availability. Its efficiency strongly depends on the climatic and hydrogeological conditions of the area of interest. In particular the structure of the underlying aquifer plays a key role. In fact, many open questions remain about the effectiveness of recharge for multi-layer aquifers, due to the complexity of their hydrogeological behaviour. In this study we perform a series of simulations aimed at assessing the effectiveness of winter/spring artificial groundwater recharge on a portion of alluvial fans in the Emilia-Romagna region (Italy). This area is a large agricultural plain which heavily relies on groundwater for irrigation. Here, aquifers are located mainly in fluvial sediment deposits of several hundred meters thickness, and in underlying marine sediment deposits. A numerical groundwater flow model has been developed in MODFLOW 6. This model is based on a previous application of MODFLOW to the whole Emilia-Romagna area by the Regional Agency for Environmental Protection (ARPAE), and extends over a wide area east of the River Secchia. Input data cover a multi-year simulation period, therefore representing seasonal variations of hydrometeorology. Calibration has been implemented by comparing observed and simulated water table levels during the period 2002-2018. Simulations are generated for various boundary conditions, mainly for different hypotheses of groundwater recharge. In particular, we assume that winter/spring recharge is increased by an assigned multiplier that is homogeneous in space over the recharge area, in order to simulate a spatially distributed artificial recharge which may be provided by winter irrigation. The results show that the effectiveness of recharge depends on the initial conditions of the aquifer and the precipitation regime during the winter season. During drought conditions artificial recharge seems to be an interesting option for risk mitigation.