Vulnerability of Mediterranean hydrosystems to ... - agire - BRGM

Extended abstractThe Mediterranean region, that includes interconnected hydro-systems in which groundwater isimportant, is subjected to a contrasted climate and an increasing anthropogenic pressure.Global warming over Mediterranean region will probably cause more warm and dry summers and lessprecipitation during warmer winters and shorter rainy seasons. These predictions set out by the lastreport of the Intergovernmental Panel on Climate Change (IPCC AR4, 2007) are rather different thanthese released by the previous assessment report (IPCC TAR, 2001), in which more rainfall waspredicted during winter. Those changes are likely to have a negative impact on water resourcesthroughout the year and will certainly complicate the current water management strategies mainlyoriented to respond to the domestic and agricultural water demand.In the Languedoc-Roussillon region for instance, the population growth (on a mean range of 1,5% peryear) is likely to provoke a substantial increase in demand for water by a rate close to 20% in the next15 years, when alternatively, the extent of irrigation systems size will be slightly decreasing in thefuture. In addition, environment-protection policies will be enhanced in the future with theimplementation of the European Water Framework directive.Within this general framework, the VULCAIN project aims to implement of an integrated(transdisciplinary) modelling method to assess the impact of climatic and socio-economic drivingforces on the Mediterranean hydro-systems at mean (2020-2040) and longer term (2040-2060).The study zone is the Pyrénées Orientales department, chosen because it contains on the one hand,specific Mediterranean hydro-systems (coastal multi-layer aquifer, karstic systems with endogenousand exogenous recharge by rainfall and water losses and three river basins controlled by dams), andon the other hand, a socio-economic context that is close to the most critical of the Languedoc-Roussillon region in terms of water demand and available water resources.This paper presents the first-year results of the VULCAIN project. Non stationarity analyses wereperformed on temperature and precipitation data series over 35 years (1970-2005). Results show anincrease of mean annual temperatures of 1,5° C over the analysed period and a general decrease ofmonthly precipitation for all seasons, excluding autumn where an increase in both the rainfall eventsoccurrence and intensity was found in November. Climate scenarios were built both from thesimulation results of five global circulation models (GCM) (involved in the IPCC-AR4 simulationgroups) under the A1B greenhouse gases emission scenario of the IPCC. Those scenarios show ageneral increase of the mean monthly temperature of 1-2°C for 2020-40 and 1.7-3.3°C for 2040-60.Relatively large differences are found between the different GCM results concerning future monthlyprecipitation, but a general decreasing trend is found for all seasons notably for 2040-60.Two main different sorts of systems contain the water resources of the study area: the Agly, Têt andTech river basins where the water management uses dams and channels essentially for irrigationpurposes of around 15 000 ha of cultivated area and the plio-quaternary aquifer of the Roussillon plainexploited for drinking water purposes (60 Mi m 3 ). Both systems are closely linked by hydraulic devicesand present a notably strong dependence on dam management strategies. A baseline scenario is indevelopment, to describe the expected evolution of economic activities depending on the waterresources and on socio-economic and political drivers of the study area. Predicted climate changescenarios are likely to produce a general runoff, soil water content, aquifer recharge reduction and tocomplicate the filling of the dams. Consequently, the increasing demand in drinking water linked to thepopulation growth is likely to face important difficulties. The impact of the climate scenarios on theagricultural water management is uncertain, as the different driving socio-economic forces mayproduce opposed impacts in this sector that could result in a reduction of water demand.Assuming that climate does not change from present, the baseline scenario will be based on theterritory expertise (using participatory protocols and actor meetings) and the evolution of regionalsocio-economic driving forces. It also will be consistent with assumptions underlying the definition ofthe SRES scenarios at a global level. Together with the climate scenarios, it will be used to forcehydrological/hydrogeological models currently in development. Aiming to develop integrated tools andmethods to the operational assessment of the global change impacts, the Vulcain project will permitthe evaluation of the future vulnerability of the exploited hydro-systems and of the supplied territory inthe Mediterranean context.3