Attribution of Lake Surface Water Temperature Change in Large Lakes Across China Over Past Four Decades.

Lake surface water temperature (LSWT) is a key parameter in lake energy budget and is highly vulnerable to climate change. However, the long‐term trends in LSWT across China and their driving factors remain uncertain. Here, we used a calibrated lake model to simulate LSWT over 1979–2018 for 91 large lakes (>100 km2) across China. Simulations reveal an overall LSWT warming trend (0.040°C yr−1, p < 0.05), but with large spatial variations. The majority of these lakes show significant warming trends (84%, 0.053°C yr−1), while a significant cooling trend is found in the seven lakes in the northwestern Tibetan Plateau (−0.064°C yr−1). LSWT of approximately 42% of the lakes increases more rapidly than the corresponding ambient air temperature. Regionally, the warming trend is highest for lakes in the Eastern Plain (0.049°C yr−1) and the lowest in the Yunnan‐Guizhou Plateau (0.016°C yr−1). The increases in simulated LSWT also vary across seasons, with a higher rate in winter and spring than in summer and autumn. Changes in air temperature, downward longwave radiation, and wind speed are the most important climatic drivers for LSWT changes. Lake surface warming could be more rapid under future global warming, necessitating greater attention to lake‐atmosphere interactions. Plain Language Summary: Lake surface water temperature (LSWT) is an essential factor in regulating heat and water exchange between lake surface and air. Previous studies have relied on satellite or in situ data to study changes in LSWT at various scales. However, the spatiotemporal variations in LSWT at a national scale and their driving factors are still poorly understood for large countries such as China. Here, we used a one‐dimensional lake model (FLake) to simulate the spatiotemporal variability of LSWT for 91 large lakes (>100 km2) across China from 1979 to 2018. Our simulations reveal a significant warming trend for most lakes, although a few lakes in the northwestern Tibetan Plateau show a cooling trend. Interestingly, 42% (38 of 91) of these lakes showed faster warming rates than nearby air temperatures. LSWT increased faster in spring and winter than in summer and autumn. Lake surface warming is mainly explained by locally rising air temperature, increasing downward longwave radiation, and weakened wind speed. Under the projected warmer climate in the future, lake surface warming is expected to continue, with important implications for lake management and climate change mitigation. Key Points: Lake model revealed a significant annual increase of 0.040°C (p < 0.05) in the surface water temperature of large lakes across China from 1979 to 2018The simulated surface water temperature warmed faster than the local surface air temperature in approximately 42% of the studied lakesChanges in air temperature, downward longwave radiation, and wind speed are the primary contributors to the trends in lake surface water temperature [ABSTRACT FROM AUTHOR]