6. Current and Future Impacts of Extreme Flood Events

Inadequate timber extraction management of forests, cattle farming, abusive recreational practices, and rapid urban expansion are all factors that create significant problems in the Cantabrian area watershed for the sustainable management of the hydrological ecosystem services. These problems, added to the consequences of climate change, are already causing tangible and intangible damage to human and natural systems. Particularly for this coastal area, it is necessary to analyse flooding on a local scale. Therefore, the impact of climate change on extreme precipitation and its influence on discharge is researched in the Atlantic climate basin in the context of short, fast-flowing rivers. In this chapter, ENSEMBLES RT3 climate model outputs are analysed and calibrated with local observation data recorded daily. The hydrological/hydraulic coupling model (MikeShe-Mike11) is applied by forcing the validated model output. In order for results to remain spatially representative, basin and urban scales are studied. According to the results, under the medium greenhouse emission scenario (A1B), the Regional Climate Models HIRHAM (2001–2050) and RACMO (2051–2100) show an increase in extreme precipitation. The expected changes show spatial variability depending on local characteristics (topography, proximity to the coast, vegetation, etc.) and ranging between 6–26 % for HIRHAM and 11–12 % for RACMO. These changes in precipitation affect the river flow. An increase of 22 ± 2 % is expected in the HIRHAM climatic model for upstream peak discharge with a return period exceeding 50 years. The change in precipitation also causes an increase in flood damage. This is a result of the expected change in the river’s peak flow by 2,050 leading to an expansion of 3 % in the flood area as well as impacting the intensity of flooding. In this context, it has been necessary to define and assess the different adaptation options.