Calibration of a Large-Scale Water Balance Model in a Semi-Arid Ungauged Catchment of Southern Italy

Despite the simplified representation of basic hydrological processes, large-scale hydrological models are increasingly adopted for studying catchment water balance and developing water resources scenarios under changing climate conditions. In this work, we analyzed the results of the BIGBANG model developed by ISPRA and available over the entire Italian territory with a spatial resolution of 1x1 km and monthly time-scale. We considered its application in an ungauged semi-arid basin of Puglia (Southern Italy) by comparison with output of a distributed model, validated at regional level and suitable for representing both the surface and sub-surface water balance at daily scale. Dealing with the application of BIGBANG monthly model in ungauged basins, we performed the validation of the daily rainfall-runoff model through the use of semi-quantitative information related to past flood events, acquired from newspaper reports, and seasonality of hydrological regime based on local knowledge. Among the parameters of the daily model, recession time of sub-surface reservoirs, together with storage capacity, were the most relevant for the likely reconstruction of hydrologic response in terms of simulated daily streamflow. Besides the monthly sum-up of daily flowrates, the comparison with the BIGBANG output allowed to investigate dynamics in the groundwater basin area in representing the baseflow component of the simulated streamflow, based on the known conceptual model of the hydrogeological setting. This example application discusses the effectiveness of the proposed approach for the exploitation of large-scale models in ungauged semi-arid basins.