Vulnerability of reed beds to climate change in the Occitanie region

International audienceReed beds communities play important structural and functional roles in wetland ecosystems, as they work as efficient filters for pollutants and provide habitat for fauna species and avifauna in particular. In the Mediterranean (GIGANTE et al., 2014), a decline of these ecosystems has been observed during the last decades, resulting mainly from eutrophication together with anoxic conditions. Intrusions of seawater by coastal flooding during storms can radically transform the balance of the environments making them, for a certain period, unsuitable for the development of the reed beds and the species they shelter. The reed beds are so vulnerable to climate change in the near future (ADENA, 2022). This study aims at assessing the vulnerability to climate change of reed beds ecosystems along the Mediterranean coast of Occitanie by comparing the topography of 29 reed beds, approximated as accurately as possible by recent topographic datasets, with marine flooding scenarios calculated for two periods: 2030-2050, 2100 and 2100+ (pessimistic scenario). A simplified static approach is used without considering duration of flooding nor the speed of water propagation. Three different scenarios are proposed at each time scale: permanent flooding, recurrent (flooding once a year without storm event) and exceptional (100y return period storm event). Water levels are defined using hypotheses of the 4 th IPCC report together with the previous studies of extreme water levels and regional storm characteristics. The first finding from the analysis is that 50% (16) of the regional reed beds will be already impacted by 2030-2050 permanently (most of the year) and seven recurrently, corresponding to a sea level rise of between +40 cm and +70 cm NGF. Most of the regional reed beds areas are impacted by the less severe scenarios, pointing out the important vulnerability of these coastal ecosystems