Lake Trasimeno - Italy

Because of small extension of the cathment basin relatively to the lake area, the water balance of the lake is strongly affected by the pluviometric regime and annual water inflows are frequently lower than evaporation losses. The strict dependence of the water balance on meteorological conditions has caused dramatic floods and droughts over the centuries and human interventions have been made in order to regulate the lake level since Etruscan or Roman times. Starting from the Middle Ages, there is a fair amount of documentation on works regarding the hydraulic regulation of the lake. The outlet restructuring, completed at the end of the 19th century, gave inception to a progressive lowering of the lake level which led to a dramatic crisis of the 1950s, to which contributed several variations of the artificial outlet threshold. The enlargement of the catchment basin performed in 1957-62, allowed the lake to rapidly recover from drought. The decreasing trend of precipitation and the increasing trend of temperature recorded in Central Italy during the last decades caused a new phase of low level. This hydrological change has been accompanied by significant modifications of the general environmental conditions: a progressive accumulation of dissolved salts, a significant increase of the total alkalinity and a reduction in the water transparency have been observed in the lake during the drought phases experienced in the last fifty years. Details and data about changes in meteorological and water quality variables can be found in Ludovisi & Gaino (2010).