River ecosystem assessmenttowards water security and environmental governance

Laburpena

Water security is key to human well-being and is one of the greatest challenges of environmental governance. It is necessary to guarantee the protection of water systems against risks such as floods or impacts that deteriorate water quality, based on comprehensive water governance policies. The research carried out in this doctoral thesis aims to develop strategies that guarantee water security in different territories of Galicia and Northern Portugal. In order to achieve this objective, firstly, an evaluation of the cause-effect interactions between the main conditioning factors that affect water quality in all the hydrological basins that make up the Galicia-Costa Demarcation is proposed. In this way, a holistic view of the various threats affecting ecological integrity is achieved using the partial least squares path modelling method (PLS-PM). The model obtained incorporates information about anthropogenic pressure as well as the positive impact of riparian vegetation on water quality. In addition, two of the main effects affecting water security in Galicia-Costa, the eutrophication process and the risk of flooding, have been evaluated for a case study (Umia River, Caldas de Reis, Pontevedra). The eutrophication process was evaluated through modelling using PLS-PM, including information on climatic conditions (temperature, precipitation). In addition, different trophic scenarios were tested, adapted to the temperature increase predicted for the study area. On the other hand, flood risk was calculated through hydrological modelling using the Hydrologic Modelling System (HEC-HMS) software. Land cover changes were detected through Sentinel-2 images and the associated flood risk was analysed. In this case, different simulations were carried out based on the use of reforestation as a management tool, taking into account that it is one of the nature-based solutions (NbS) that can best reduce flood risk. These simulations were planned in different areas of the basin to assess their contribution to water retention as well as to the reduction of peak flows. Finally, the effects of management plans carried out in a case study (Olo River, Northern Portugal) over 10 years have been evaluated. This has allowed us to obtain a comprehensive view of the conservation and improvement actions carried out, analysing their successes and failures. In conclusion, this doctoral thesis has evaluated the use of different tools with the potential to improve hydrological-forest management. It has been shown how the models carried out and the use of satellite images, together with the use of other instruments such as predictive scenario analysis, would facilitate the decision making that corresponds to water management and integrated organisational management at the river basin level. These tools have proven to be effective in assessing the status of water bodies, as well as in providing information on possible changes that will affect water security, such as climate change and anthropogenic pressures. The use of these models constitutes a promising tool for the competent administration, allowing multi-objective optimisation of possible solutions to be taken, as well as encouraging the development of complex and multidisciplinary measures.