Assessment of agronomic adaptation strategies to climate change in a Mediterranean watershed with SWAT+

The Mediterranean region is considered a hotspot for climate change as it is expected to face more severe impacts compared to other regions of the world. To better understand these impacts and plan more effective adaptation strategies, integrated assessments should consider not only biophysical aspects, but also social, political, and economic ones. Plenty of models are available to simulate these various aspects, but certainly, the more models are included, the higher the complexity, which severely affects the reproducibility of the studies. Even when considering only biophysical aspects, related for example to water and food security, individual crop and/or hydrological models have intrinsic limitations. Integrated, distributed, agro-hydrological models such as the Soil and Water Assessment Tool (SWAT) might be the solution to overcome some of these drawbacks, including the point-scale nature of crop-growth models.

We applied the SWAT+ model in a medium-sized agricultural watershed in Central Italy, the Ombrone watershed, in order to comprehensively assess climate change impacts on crop production and water management and evaluate autonomous agronomic adaptation strategies. By forcing SWAT+ with five bias-corrected EURO-CORDEX climate models, we assessed future precipitation and temperature in the study area. Moreover, we simulated the fluxes of different water balance components and evaluated how they were affected by the increasing CO₂ concentration. Then, we simulated future crop yield and water footprint of three representative crops - durum wheat, sunflower and irrigated maize - and evaluated the adaptive capacity of the agricultural systems by simulating simple adaptation strategies such as shifting sowing dates and applying supplemental irrigation. Finally, we estimated the effects of these adaptation strategies on water balance components.

While the temperature was predicted to increase, future precipitation showed much more uncertainty. Furthermore, considering the CO₂ fertilization effect enhanced the uncertainty about future aridity conditions, with variables such as potential evapotranspiration that varied up to 50% when considering constant or increasing CO₂ concentration. Crop yield was negatively affected mainly by the reduction of crop cycle length caused by increased temperatures, but with adaptation strategies it was possible to reduce losses or even obtain higher production. Finally, management changes such as the inclusion of cover crops in the crop rotation have a significant impact on some water balance components that cannot be neglected. The results of this study show the increasing need to adapt to climate change impacts in the Mediterranean cultivated catchments.