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The Tibetan Plateau (TP) plays a significant role in the Earth's climate system. This letter examines the nighttime lake surface water temperature (LSWT) of 374 lakes (>= 10 km(2) each) over the TP for the past 15 years (2001-2015). An overall warming trend (0.037 degrees C/year) is found and it is consistent with the warming air temperature (0.036 degrees C/year) over the TP, with the vast majority of the lakes (70%, with 28% of which are significant) showing warming (0.076 degrees C/year) and the rest (30%, with 37% of which are significant) showing cooling (-0.053 degrees C/year). This astonishing contrast was controlled by different water sources recharging these lakes: (1) warming LSWT due to increased precipitation (central and northern TP) or permafrost degradation (northwestern TP) and (2) cooling LSWT due to increased glacier meltwater (southwestern TP), revealing LSWT a sensitive indicator to climate change that triggered different regional responses in precipitation, permafrost, and glacier changes over the TP. This study helps improve our understanding of high-altitude lakes and their changing mechanisms under the warming climate.

Plain Language Summary The Tibetan Plateau (TP), a vast highland area in Asia, plays a significant role in the Earth's climate system. Here we examine the nighttime lake surface water temperature (LSWT) of 374 TP lakes (>= 10 km(2) each) over the past 15 years (2001-2015). An overall warmin trend (0.037 degrees C/year), consistent with the warming air temperature (0.036 degrees C/year) over the TP, is found, with the vast majority of the lakes (70%) showing fast warming (0.076 degrees C/year) and the rest (30%) showing fast cooling (-0.053 degrees C/year). This astonishing contrast was controlled by different water sources recharging these lakes: (1) warming LSWT due to increased precipitation (central and northern TP) or permafrost degradation (northwestern TP) and (2) cooling LSWT due to increased glacier meltwater (southwestern TP). Although there are clear regional differences in precipitation, permafrost degradation, and glacier melt, these changes were all due to the warming air temperature over the TP. This study reveals that LSWT is a sensitive indicator of the climate change that triggered different regional responses in precipitation, permafrost, and glacier changes over the TP. This study helps improve our understanding of high-altitude lakes and their changing mechanisms under the warming climate.