Modelling the impacts of climate and land use changes on water quality in the Guadiana basin and the adjacent coastal area

The increasing pressure on water resources and the management problems related to it, highlight the need of a multidisciplinary approach in the hydrological, social, economic and ecological field, applicable to every considered catchment. Changes in land use means changes in quantity and quality of water resources; this scenario could be more severe with the intensification of some chemical and physical processes, as a consequence of climate change. Based on this concept, the present work has been developed to support the use of information systems tools in the decision making process, from integrated river management to the integrated coastal management. For this purpose, it is used a hydrological model, using the Guadiana catchment as case study. The model has been calibrated and validated for river flow and nitrate load with satisfactory results, and then it was used for water quality simulation. Furthermore, simulations were done under two future Climate Change (CC, Representative Concentration Pathway — RCP 4.5 and RCP 8.5) scenarios, three Land Use Change (LUC) scenarios and the combination of both of them, to evaluate their contribution to the nutrient concentration that reaches the estuary. In this study, an extension of land use change from forest to olive groves would produce a greater contribution of nutrients under the most abrasive climate change scenario (RCP 8.5). Such scenario could be beneficial for the productivity of estuarine ecosystem. The same change in land use, instead, is not recommended under a climate change scenario RCP 4.5, as it would cause a net reduction in the supply of nutrients to the estuary. With this information as support, it can be sought solutions with policies and incentives that are considered convenient and that allow to control, prevent or correct the deterioration of water bodies and thereby accomplish with the quality levels required by European Directives.