Chinese ice-lake line shifts under climate change

Lake ice is a sensitive indicator of climate warming, yet a spatially explicit metric for where lakes freeze across China remains limited. Here we propose an ice lake line, defined as the lowest latitudinal connection of frozen lakes within each longitude band, to delineate the boundary below which lakes cease to freeze. We define the ice season as at least 10 consecutive days with lake surface water temperature below 1 °C and analyse 1,705 lakes that experienced ice cover during 1980 to 2021.

 

We found that the ice lake line for normally frozen lakes shifted north from 32.10° N in the 1980s to 32.42° N in the 2010s, equivalent to 0.32° or about 36 km over four decades. The boundary occurs at lower latitudes in western China and higher latitudes in the east, consistent with strong elevation control. Over the same period, ice on was delayed by 9.7 days, ice off advanced by 12.7 days, and ice duration shortened by 20.7 days as median changes, while about 39 lakes ceased to freeze by the 2010s. By 2090 to 2099, projections indicate 3, 77, 226 and 393 fewer winter freezing lakes than in the 2020s under SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5, respectively, with the ice lake line moving to 33.97° N, 34.72° N, 35.30° N and 35.75° N. The faster northward shift for completely frozen lakes indicates a growing prevalence of partially frozen conditions. These results establish the ice lake line as an intuitive indicator of rapid warming and show that emissions mitigation can markedly slow the reorganization of China’s lake ice regime.