Balancing flood mitigation and water availability through smart afforestation

Strategic ecosystem restoration is central to achieving both climate resilience and biodiversity goals. The EU Biodiversity Strategy for 2030 calls for converting at least 10% of agricultural land into high-diversity landscape features. However, the hydrological implications of such vegetation-based transformations remain underexplored. At the same time, effective water policy requires actionable insights into how land-use interventions interact with a changing climate. Vegetation plays a pivotal role in hydro-meteorological extremes, influencing evapotranspiration, soil moisture dynamics, infiltration, and runoff generation. Here, we use a kilometre-scale hydrological model integrated with a machine learning optimisation algorithm to evaluate the impacts of afforestation on European water systems under both current and +2°C warming conditions. Three afforestation scenarios — ranging from a hypothetical full land conversion to smart, spatially targeted, biodiversity-aligned strategies — were tested for their effects on evapotranspiration, river discharge, and groundwater levels. Results reveal that smart afforestation reduces seasonal flood peaks by up to 15%, with the strongest effects observed in Central Europe during winter. It also improves groundwater resilience by tripling minimum storage during dry periods, despite a modest 5% decline in average levels. While climate warming results in a 16% reduction in water availability, afforestation leads to a smaller, consistent 6% decrease that remains stable across climate scenarios. Zones with 40–50% forest cover offer the most effective balance, maximising flood mitigation and buffering hydrological drought risk. These findings emphasise the importance of nature-based solutions, such as spatially targeted afforestation, as viable strategies to moderate hydro-meteorological extremes and enhance climate-adaptive water management.