Assessing the Role of Irrigation in Groundwater Recharge in the Po Valley

The Po Valley, Italy's largest and most economically significant region, heavily relies on intensive irrigation to sustain its very productive agriculture and meet the demand of a variety of high-value food productions. Historically, the region's agricultural success has been driven by widespread traditional surface irrigation systems, which primarily draw water from rivers and deliver it to fields through an extensive network of irrigation canals. These systems, that in many areas have been operational for centuries, not only enhance agricultural productivity but also contribute to groundwater recharge, helping to mitigate river droughts and seasonal fluctuations in surface water availability. In recent years, however, declining surface water availability and increasing reliance on groundwater extraction have already been observed, because of a higher variability of summer precipitation and decreasing winter snow accumulation in the Alps caused by climate change. Consequently, accurately estimating groundwater recharge from irrigation excess has become crucial. Despite its importance, the impact of irrigation on groundwater recharge across the Po Valley remains poorly investigated. This is mainly due to the complexity of the region's hydrological systems characterized by strong interactions between groundwater and surface water, and to the lack of reliable data covering the entire Po Valley. In the context of MidAS-Po project, a methodological approach has been developed for the preliminary estimation of groundwater recharge through percolation from irrigated areas and seepage from irrigation channels over the whole Po Valley. This approach involves two main steps. First, the application of a distributed agro-hydrological model, IdrAgra-Po, simulating daily soil water balance terms, including percolation from the agricultural soil layer (1 meter deep) in irrigated fields. The model was implemented over the period 2010–2022, with a spatial resolution of 0.25 km², and incorporates several input datasets: i) agro-meteorological conditions from the E-OBS dataset, produced by the Copernicus Land Monitoring Service of the European Environment Agency; ii) soil hydro-pedological data sourced from four regional databases, processed and harmonized over the study area; iii) land use data provided by the CORINE project and integrated with local information; and iv) depth of the shallow groundwater table. The second step is the estimation of groundwater recharge due to seepage from the irrigation network using a simplified methodology that relies on the data of the national agricultural information system SIGRIAN. This approach estimates channel seepage as the ratio between the measured water volumes allocated upstream of the irrigation districts into which SIGRIAN splits the Po Valley and the irrigation requirements determined by the IdrAgra-Po model for the same districts. The resulting preliminary estimate of groundwater recharge linked to irrigation practices represents a significant step toward understanding the role of irrigation in the aquifer recharge in Po Valley. However, further investigations should be conducted to improve the quality of the input data, mainly, information on local irrigation methods and practices, land use and irrigation volumes diverted from rivers and withdrawn from aquifers. Acknowledgment This contribution is presented in the framework of the MidAS-Po project, funded by Italy's Development and Cohesion Fund - FSC 2014-2020.