Impacts of Climate Change on Freshwater Bodies: Quantitative Aspects

In this chapter we present the results of the impact assessment on freshwater bodies in the Mediterranean region. Starting from the characterization of the general features of Mediterranean hydrology, main focus is given on large river basins discharging into the Mediterranean sea as well as to small and medium scale catchments representing almost half of the entire discharging basin. Groundwater representing a fundamental water resource for Mediterranean countries was also considered. Climate change impacts on the hydrological behavior of large river basins is investigated through the IRIS computational tool which was proved to be a versatile instrument for both climate studies and the assessment of model ability to simulate the hydrological cycle at catchment scale, taking advantage of the available observed discharge series to evaluate the reliability of future discharge projections. The results regarding some representative Mediterranean rivers using multiple climate models developed inside Circe have highlighted an open spread among twenty- fi rst century projections. The problem of the effective information content of climate model simulations with respect to small scale impact studies is developed at the scale of medium and small catchments. Particularly at the space-time scales needed to describe the terrestrial water cycle in Mediterranean environments this is recognized among the most dif fi cult problems facing both science and society. Therefore downscaling and bias-correction requirements have been treated in this chapter through speci fi c methodologies which integrate dynamical downscaling with statistical downscaling always adopting ground based observation of climate variables as a powerful means to obtain more robust climate forcing for hydrological models. The assessment of climate change impacts on small and medium size catchments is developed through some representative case studies in which downscaling methodologies have been applied thanks to the availability of dense climate measurement networks. The impact assessment of water resources in the Apulia region (southern Italy) revealed a marked increase in the variability of hydrologic regimes as consequence of the increased rainfall variability predicted for the twenty- fi rst century. Conversely only slight decreasing trends were detected in the annual water balance components. Similar results were found on a carbonate aquifer in Southern Italy in which a large Apennine spring have been selected as a signi fi cant hydrogeological systems with minimal anthropogenic pressures in the recharge areas. Finally a speci fi c session is dedicated to the role of arti fi cial dams in reducing the possible impacts of climate change. In particular, methodologies for the assessment of optimal dam dimensioning under climate change are presented as well as a reliability assessment based on water supply and demand imbalances.