Change from nival to pluvial recharge of the aquifer leads to a warmer lake

Global warming is affecting aquatic ecosystems worldwide, with mountain areas particularly vulnerable. Climate models are predicting changes in winter precipitation patterns, particularly at mid-altitudes, with probable effects on lake functioning. Lake Tovel (1177 m above sea level), a deep (39 m) aquiferfed lake in the Brenta Dolomites (Italy), showed unusually high water temperatures in 2017 notwithstanding average air temperatures and precipitation. The years from 2000 to 2016, including the hot European year, 2003, and the locally warmest year, 2015, did not show comparable water temperature increases, as shown by a principal component analysis. Volume weighted mean water temperature from June to September 2017 was 1.9-2.6 °C higher than long-term temperatures (2000- 2016). We linked this strong temperature increase to the lack of snow during winter 2016/2017.