Assessment of alternative water storage strategies in a Mediterranean catchment in a changing climate

Droughts and water scarcity are increasingly challenging agricultural production and increasing water storage is a common solution. In the Orcia catchment – Tuscany region, Central Italy – the main type of storage is represented by Small Agricultural Reservoirs (SmARs), which were largely realized in the 20th century to boost agricultural production of herbaceous crops. Recently, the underutilized SmARs (>1000 with an average area of 0.15 hectares) received renewed interest due to the challenges posed by climate change. Rising temperatures and erratic precipitation patterns threaten the high-quality productions of the Orcia catchment, which now often requires supplemental irrigation during summer. At the same time, as a response to recent droughts, institutions are promoting the realization of a large reservoir (17 million m³) in the Orcia catchment. In this study, we aim to simulate the two types of water storage and assess climate change consequences on the future water stored. To represent them, we use the flexible and integrated Soil and Water Assessment Tool Plus (SWAT+). The model is calibrated and validated for monthly streamflow and basin actual evapotranspiration through an unusual approach of finding the best parameters in a “simplified” model set-up, and then transferring them to the so-called “complex” model (which requires very long simulation run time and includes the SmARs). We set up alternative models to represent the conditions without any type of water storage, both combined and only the SmARs or the large dam. Then, we use five General Circulation Models under the Business as Usual emission scenario to simulate the implication of climate change on future water stored in the Orcia catchment until 2100. In response to the decreasing precipitation and increased temperature, the outputs of the validated SWAT+ model show a decline in water flowing into the reservoirs (-30%) and a surge in evaporation from the reservoirs (8.7%). This will have consequences on the future water stored that is expected to decrease (-6.2%) by the end of the century. Additionally, infiltration from the bottom of the reservoirs will also decline (-10%), hence reducing aquifer recharge. While the trends assessed with the Mann-Kendall test are often significant, these are strongest when considering only the summer season or only the SmARs. Therefore, preliminary results show that SmARs might be more susceptible to climate change compared to large dams. As SmARs remain a crucial adaptation strategy to climate change, these aspects should be considered in sustainable water management and planning in the Orcia catchment.

Acknowledgments

This research was carried out within the AG-WaMED project, funded by PRIMA, an initiative supported and funded under Horizon 2020, Grant Agreement Number No. [Italy: 391 del 20/10/2022, Egypt: 45878, Tunisia: 0005874-004-18-2022-3, Greece: ΓΓP21-0474657, Spain: PCI2022-132929, Algeria: N° 04/PRIMA_section 2/2021], and the RETURN Extended Partnership funded by the EU Next-GenerationEU (NRRP, Mission 4, Component 2, Investment 1.3 – D.D. 1243 2/8/2022, PE0000005). The content of this abstract reflects the views only of the authors, and the Commission cannot be held responsible for any use that may be made of the information contained therein.