The GEOframe system deployment in the analysis of water availability and scarcity in the Po River Basin District and model calibration strategies

As observed in the last years, extreme events, floods and droughts, have been reported to be more likely due to climate change and environmental modifications, and Italy in particular, experienced more frequent and intense drought events, with an exceptionally severe drought in 2022.

To cope with this kind of phenomena and to update the existing numerical modelling for water resource management, in 2021 the Po River District Basin Authority (AdBPo) started the implementation of the GEOframe modelling system on the whole territory of the district, aiming to provide a better quantification and forecast of the spatial and temporal water availability in its territory.

The GEOframe modelling system (Abera et al. (2017)) is a completely open-source semi-distributed conceptual model, developed by a scientific international community led by the University of Trento, characterized by a high modularity and flexibility.

The model, after the meteorological data spatial interpolation, and the geomorphological analysis, enables the simulation of all the components of the hydrological balance (e.g.: evapotranspiration, snow accumulation, water storage and water discharge).

The reference time period is the 1991-2020 time range and all the simulations processes take place in the “Hydrological Reference Units” (HRU), namely the subbasins obtained from the geomorphological analysis.

In this case the average area of the subbasins is set at 10 km² (generating nearly 3000 HRUs), considered as a good compromise between the simulation precision and the computational space and time needed.

Consequently, the model parameters calibration was carried out according to a “zonal calibration” strategy in which the parameters are calibrated in different hydrometers. This is the most computational time-consuming phase of the model implementation, for this reason a 3 hydrological years period was selected, on the basis of water discharge data availability in the different regions of the district.

The calibration was carried out with the KGE method and consists in the research of the values of the characteristic model parameters which fit the discharge evolution recorded in the hydrometers in the best possible way, comparing the simulated discharge trend with the measured one.

The calibration of the model, as its implementation, has started in the Valle d’Aosta region, the most upstream part of the district, and proceeded going downstream, through Piemonte, Emilia-Romagna and Lombardia, for a total of about 150 calibrated hydrometers.

Due to the huge surface and the high complexity of the study area and of the hydrometers distribution, different actions and strategies have been tested to improve the calibration results and efficiency.

With the completion of the calibration phase, it was then analysed the impact of water scarcity on agriculture and taking a particular attention to the snow precipitation contribution.

In conclusion, thanks to the modularity of the GEOframe model, it was possible to work collaboratively on the calibration phase, lowering the time needed and improving the calibration efficiency, exchanging the results obtained and the strategy to calculate them and to carry out an analysis on water availability in the Po River Basin District up to Pontelagoscuro (FE).