Evaluating the Water Level Variation of a High-Altitude Lake in Response to Environmental Changes on the Southern Tibetan Plateau

Lakes are sensitive to environmental changes, and an example of this change is the decreased water level in the Yamzho Yumco Lake (YYL, in southern Tibetan Plateau), which is opposite of the reported expansion in most other lakes of the Tibetan Plateau. In this study, we report a high-resolution dataset of daily monitored water levels from 1974 to 2010 in the YYL, which was used to elucidate annual and seasonal variations of the lake water level. These data are coupled to the stable isotope signals in the lake water and to a water balance model to provide an overall picture of factors and processes affecting the lake. The data revealed an annual average rate of 0.12 m per year lowering of the lake water level, but there was a relative increase in the summer and autumn seasons. It was found that a large amount of precipitation and low evaporation were primary reasons for increasing periods of the lake water level. The extensive glacier melting process driven by a sharp rise in temperature is another key factor for the increasing period between 1997 and 2004. The annual general water level decline before 1996 is attributed to the slow glacier melting rate and reduced precipitation, while a drastic decline of the water level after 2005 could be related to water leakage at the lake bottom, enhanced by a thawing of the permafrost. This process is driven by increasing soil temperatures and human activity. Finding out the causes of the YYL shrinkage trend provides vital implications for the management of water resources in the Tibetan plateau cold regions.