Impact of climate change on the hydrology of the shallow Lake Trasimeno (Umbria, Italy): history, forecasting and management

Lake Trasimeno is the largest lake of the Italian Peninsula. Because of the small extent of its watershed, meteorological conditions have caused dramatic floods and droughts over the centuries. Although numerous attempts have been made to regulate the lake level since Etruscan or Roman times, the problems related to water level changes remain unsolved, and the recently adaptive management strategies seem to be ineffective in the current climatic conditions. This study evaluates past and future management scenarios with the aim of identifying effective strategies to limit the lake level fluctuations. A lumped hydrological model, which incorporates climate forcing and water regulation policies adopted currently and in the past, is calibrated and validated using a fifty-year data series. Future scenarios (present2090) of water level change are simulated on the basis of IPCC (Intergovernmental Panel on Climate Change) regional projections for precipitation and temperature. Possible mitigation measures, such as those involving the enlargement of the catchment basin, the water diversion from nearby dams and the adoption of more restrictive rules on abstractions are also considered. The model indicates that critical prospects emerge if the intermediate or the maximum rates of change estimated by global climate models are assumed. Under these circumstances, currently feasible mitigation measures seem effective in preventing severe water shortage in the next decades, but ineffective in preventing the drainage of the lake in the second half of the century. We recommend that plans for water resource management should be put in place as a matter of urgency to ensure the conservation of the hydrologically vulnerable Lake Trasimeno.