Thermal regime, energy budget and lake evaporation at Paiku Co, a deep alpine lake in the central Himalayas

Abstract. Evaporation from hydrologically-closed lakes is one of the largest components of their lake water budget, however, its effects on seasonal lake level changes is less investigated due to lack of comprehensive observation of lake water budget. In this study, lake evaporation were determined through energy budget method at Paiku Co, a deep alpine lake in the central Himalayas, based on three years' in-situ observations of thermal structure and hydrometeorology (2015–2018). Results show that Paiku Co was thermally stratified between July and October and fully mixed between November and June. Between April and July when the lake gradually warmed, about 66.5 % of the net radiation was consumed to heat the lake water. Between October and January when the lake cooled, heat released from lake water was about 3 times larger than the net radiation. Changes in lake heat storage largely determined the seasonal pattern of lake evaporation. There was about a 5 month lag between the maximum lake evaporation and maximum net radiation due to the large heat capacity of lake water. Lake evaporation was estimated to be 975 ± 39 mm between May and December during the study period, with low values in spring and early summer, and high values in autumn and early winter. The seasonal pattern of lake evaporation at Paiku Co significantly affects lake level seasonality, that is, significant lake level decrease in post-monsoon season while slight in pre-monsoon. This study may have implications for the different amplitudes of seasonal lake level variations between deep and shallow lakes.