Quantifying groundwater resources is an important issue for effective water resource planning and management at river basin scale and it has to take into account all the natural and anthropogenic components of the water balance, i.e.: rainfall and runoff processes, as well as mutual interactions between surface water and groundwater, but also artificial groundwater recharges (i.e. from irrigation) and groundwater extractions.

Here, a DEM-based methodology is applied to the case study of northern Etna groundwater system and Alcantara river basin. This method, also known as reverse hydrogeological balance method, allows us to estimate the active mean annual recharge based on precipitation, temperature and potential evapotranspiration in the area.

The main objective of this study is to quantify how the DEM resolution influences the groundwater resource estimation through the above-mentioned methodology and how this is also influenced by the method for potential evapotranspiration assessment.

Groundwater and surface flow for our case study have been evaluated for 5 different DEM resolutions (20, 60, 100, 300, 500 meters) and with 3 different theoretical approaches for evapotranspiration calculation (Turc Method, Modified-Turc Method, and Budyko Method).

Results are validated against isochronous recorded data of river discharge at Moio Alcantara cross-section and show how the reverse hydrogeological balance method shows better performances if implemented with the Budyko Method for estimating evapotranspiration and by using a DEM with 60x60m grid resolution.