Evaluating the Effects of Different Adaptation Strategies to Climate and Land Use Change upon Water Fluxes in the Ave Watershed, Portugal

The increasing variability and extremes of hydrological cycles driven by climate change present critical challenges to water resource availability, raising the likelihood of floods and droughts. Understanding the potential impacts of changing climate patterns on future water resources is essential for developing effective adaptation strategies. Within the framework of the DISTENDER project (EU Horizon-ID 101056836), we focus on assessing the resilience of European watersheds to climate stressors by modeling future water scenarios and identifying sustainable water management practices.

This research comprehensively examines the impact of climate and future land use changes on extreme events in Ave Watershed in Northern Portugal using the MIKE SHE hydrological model. Future climate change projections (2021 to 2050) and Shared Socioeconomic Pathways (SSPs) were obtained from CMIP6 and were statistically downscaled. Annual 1-day and 3-day high runoff were used as a proxy for the extreme high runoff characteristics. We then evaluate three adaptive strategies for those impacts:

• Nature-based solutions: Restoring wetlands identified in the "Extended Wetland Ecosystem data," implementing sustainable agricultural practices, and adopting low-impact development methods like green and sponge cities.
• Technical solutions: Introducing new reservoirs in sub-watersheds lacking reservoirs to simulate cumulative effects of rainwater retention, check dams, or other storage infrastructures.
• Hybrid approach: Combining nature-based and technical solutions to maximize the benefits of water resources management.

The climate effects show an increase in the future 1-day and 3-day flood magnitudes across all gauges and return periods. The 100-year 1-day flood in Ave River is projected to range between 496 m³/s (33% increase in SSP 3-7.0) and 721 m³/s (94% in SSP 5-8.5), compared to 372 m³/s during the reference period (1980-2020). Future land use maps for 2020–2050 were generated using the CORINE land cover and the iCLUE model based on different SSPs. Incorporating these maps into the hydrological model shows further intensification of extreme events. For instance, using the 2050 land use map, the 100-year 1-day flood is expected to range 664 m³/s (77% in SSP 3-7.0) and 866 m³/s (133 % in SSP 5-8.5) compared to the reference period. Simulations of the adaptation strategies show that nature-based solutions can reduce flood peaks by 22–32%, while technical solutions achieve 20–46% reductions, depending on the SSP. The hybrid approach demonstrates the most efficient adaptation solution, reducing flood peaks by 37–67%. For SSPs 2-4.5 and SSP 3-7.0, the hybrid approach brings flood peaks close to those observed during the reference period.

By analyzing these strategies individually and collectively, the study identifies the hybrid approach as the most effective for enhancing resilience to extreme events and ensuring the sustainability of water resources. Efficacy analyses of adaptation options are essential to guide a stakeholder dialog and facilitate the necessary transformation. DISTENDER provides a methodological framework to identify and develop climate adaptation and mitigation strategies by integrating these results into a decision-support system.

Keywords: Adaptation strategies, Climate change, Land use, CMIP6 Climate Model, MIKE SHE, Ave catchment