Impacts of future climate change on water ecosystem services in the watershed of river Homem (Northwest Portugal)

Abstract

Se pronostica que el cambio climático afecte los recursos hídricos y cause graves impactos en las cuencas hidrográficas, reduciendo la capacidad de los ecosistemas para proporcionar servicios ecosistémicos hídricos. El objetivo de este estudio realizado en la cuenca del rio Homem (noroeste de Portugal) fue evaluar cómo el cambio climático futuro puede influir en los recursos hídricos. El modelo SOIL and Water Assesment Tool (SWAT), un modelo hidrológico calibrado y validado para las condiciones locales de la cuenca (en comparación con el caudal diario/mensual y los volúmenes mensuales del reservorio). Las proyecciones climáticas futuras (2020-2050) fueron aplicadas en el SWAT basadas en cuatro modelos climáticos regionales y dos escenarios de cambio climático (RCP 4.5 y 8.5). Nuestros resultados confirmaron que SWAT tiene un buen desempeño de cuantificación de los servicios ecosistémicos hídricos locales. El cambio climático afectaría la provisión hídrica al reducir la cantidad de agua en un 7% según RCP 8.5. Estos resultados son de gran relevancia para la elaboración de estrategias de adaptación de para reducir los impactos del cambio climático y enfatizan la necesidad de evaluar los impactos del cambio a nivel local para apoyar estrategias para el manejo sostenible de cuencas.

The watershed of river Homem, in northwest Portugal, is an important water source for hydropower production, agricultural and urban use, and tourism activities, as well as for biodiversity conservation. Climate change is expected to alter the water cycle. In fact, climate models project an increase in temperature and a decrease in precipitation, affecting water resources and the provision of ecosystem services, in particular at the local level. The general objective of this study, performed in the watershed of river Homem, was to evaluate how future climate change may influence water resources, in order to support decision-making for watershed management. Two specific objectives were addressed: (i) to assess and map the baseline status of water ecosystem services provision; and (ii) to simulate how future climate change will potentially affect the provision of ecosystem services. Modelling exercises can be useful tools to forecast climate change impacts on ecosystem services provision. The Soil and Water Assessment Tool (SWAT) was calibrated and validated for the local conditions of Homem watershed (against daily and monthly discharge and monthly reservoir volumes). Future climate projections (2020-2050) were forced in SWAT, based on four regional climate models and two climate change scenarios (RCP 4.5 and 8.5), to be compared with the historical reference period (1970-2000). Our results confirmed that SWAT has a good performance in quantifying local water dynamics to support estimates of water ecosystem services. Climate change can affect the provision of water services in the focal watershed by reducing the quantity of water by 7% under RCP 8.5, also decreasing the high and low flows during wet and dry months, respectively. Reservoir volume may decrease and severely reduce hydropower production potential, mainly in summer. Soil erosion may increase by 76% (0.26 t/ha year), although still below the threshold of 1t/ha year established as tolerable rate (i.e. compensated by soil formation). These results are of high relevance for building adaptation strategies to reduce climate changes impacts, especially taking into consideration the current European Union focus on nature-based solutions. Overall, our results emphasize the need to evaluate the impacts of climate change at the local level to support strategies for sustainable watershed management.