Optimized afforestation reduces flood risk and limits water loss in Europe

Abstract Afforestation is a nature-based solution with significant potential for mitigating climate change. The European Union’s Biodiversity Strategy for 2030 targets converting at least 10% of agricultural land into forest. However, large-scale afforestation can increase evapotranspiration, potentially exacerbating water scarcity. In this paper, we introduce a data-driven method to select optimal sites for afforestation to minimize negative effects on hydrology. We benchmark this optimized strategy against a non-optimized approach that increases forest cover randomly. Data-driven optimized afforestation reduces peak river discharges up to 43%, while evapotranspiration losses are 60% lower. The non-optimized strategy only reduces peak discharge marginally, and groundwater losses are up to three times higher. A +2°C warming scenario affects both strategies equally negatively. These findings emphasize that an optimized spatial distribution of afforestation can have a positive hydrological impact. Climate and land-use policies should employ optimized afforestation in planning to ensure benefits for both climate mitigation and water sustainability.