Participatory modeling of small reservoirs in the Orcia watershed, Italy

The Central Italian landscape is characterized by the presence of thousands of small reservoirs. The majority was dug in the 80s after strong incentives linked to agricultural production. Nowadays, most of them are not used due to various problems, either specific to reservoirs (e.g. siltation) or general (e.g. abandonment of rural areas and lower incentives for production). Concerns about the changing climate, with impelling water shortages due to increased evapotranspiration and altered rainfall patterns, raised the interest in the reutilization of these reservoirs for irrigation purposes. Indeed, typical rainfed crops such as vineyards and olive groves now often need to be irrigated in the drier seasons to obtain satisfactory productions, both in terms of quality and quantity.

Within the AG-WaMED project, we aim to understand the current situation regarding this type of non-conventional water considering economic, hydrological and governance aspects. A fundamental methodology in the project is the application of the Soil and Water Assessment Tool + (SWAT+) agro-hydrological model to simulate hydrological fluxes.

In the Orcia watershed, more than 1000 small reservoirs are present. To have a model with a reasonable simulation run time, we included in the setup of the model only those larger than 5000 m², which correspond to 54 small reservoirs. With this model setup, we run sensitivity analysis, calibration and validation using monthly actual evapotranspiration at the basin scale from the MODIS remote sensing product. We obtained more than satisfactory performances for calibration and validation (NSE > 0.8 and PBIAS < 2% for calibration, NSE > 0.6 and PBIAS = -10.1% for validation).

The inclusion of a high number of reservoirs and the good values for the model performances are promising for the application of the SWAT+ model to study non-conventional waters at the basin scale but maintaining a high level of detail. Further steps are the calibration and validation with additional variables (e.g. soil moisture, streamflow), a refinement of the model setup and the simulation of alternative management strategies and scenarios. These aspects will be discussed in future workshops together with key stakeholders (farmers, experts, decision-makers and academics) in an iterative and participatory approach. In this way, we aim to obtain an improved and more representative model and to maximize the applicability of its outputs. 

This research was carried out within the AG-WaMED project, funded by the Partnership for Research and Innovation in the Mediterranean Area Programme (PRIMA), an Art.185 initiative supported and funded under Horizon 2020, the European Union’s Framework Programme for Research and Innovation, Grant Agreement Number No. [Italy: 391 del 20/10/2022, Egypt: 45878, Tunisia: 0005874-004-18-2022-3, Greece: ΓΓP21-0474657, Spain: PCI2022-132929].

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