Resolving the water budget of a complex carbonate basin in Central Italy with parsimonious modelling solutions

Placed at the center of the Mediterranean, the Apennines chains provide a critical water supply for people living in the Italian Peninsula. Yet, the quantification of water resources in this region is challenging given that the different components of the water cycles (i.e., snowmelt, evapotranspiration, and subsurface water recharge) are highly variable in space and time due to the specificity of the climate, the reforestation trend, and the complex landscapes and geology. In this study, we investigated the challenging hydrological river regime of a complex carbonate basin with significant external (and partially karst) groundwater contribution – the Upper Nera basin – affected by recent important seismic sequences.

When dealing with such type of basins, the generic approach to delineate the basin boundaries based on the geomorphology of the area can lead to questionable results potentially yielding significant water budget imbalances. Therefore, both (hydro)geological and hydrological features have to be considered for understanding the challenging hydrological behavior of these basins.Here we proposed a specific analysis of precipitation-runoff time series corroborated with hydro-geological survey to obtain information on basin response time and the true contribution area of the basin. We applied the extreme versatility of the
GEOframe-NewAge modeling system to simulate the significant fraction of external groundwater contribution by embodying hydrogeological information of the area obtained by surveys and the hydrological analysis in a conceptual reservoir approach. We validated the model against in situ discharge observations and with remote sensing information of evapotranspiration and snow.
We show that the model (tested with several hydrological signatures and a new conceptual evaluation based on an empiric probability function) performs relatively well in reproducing the different water balance components and that the upper river basin is significantly impacted carbonate rock river discharge (i.e., up to 85% in proportion to the total discharge for some stations) coming from outside the geomorphological boundary of the basin. Yet, the groundwater recharge effects on the river, gradually attenuates at the outlet of the basin (Visso station). You can access the preprint by clicking on the Figure above.