Impact of climatic changes on hydrological systems: the case of lake Trasimeno (central Italy)

According to various Authors, a negative trend in rainfall and a slight increasing trend in temperature have been taking place in Central Italy since the end of the last century. These climatic trends can be traced to the increase in temperature seen on a global scale (i.e. "Global Change"). A decrease in rainfall of up to 20-30% can be expected for the next 50 years in the Western Mediterranean area and the Italian peninsula, should the detected trends continue. Lake Trasimeno has an average surface area of about 121 km^2 and a maximum depth of about 5 m; it has one artificial outlet and is a natural protected area. The lake level is highly variable, on both a seasonal and a pluriannual scale, and this is closely related to local rainfall. At present a stage of low levels is occurring, caused at least in part by the decrease in rainfall in the area. In this work a monthly lake level simulation model was developed. Once calibrated, the model was used to simulate the effects of different climatic situations on lake levels. The results show that, should the detected climatic trends continue, a considerable decrease in the average level is to be expected during the next few decades. This would cause a large decrease of the volume of water stored in the lake and, therefore, a deterioration of the water quality. According to these results, in order to minimize the impact of climatic changes, a better lake management is necessary, with interventions such as artificial enlargement of the catchment basin and restrictions regarding the amount of water being taken from the lake and the basin for irrigation.