Lake Cold Spells Are Declining Worldwide.

Extremes in lake surface water temperature can have profound impacts on ecosystems. Although extensive research has been conducted on lake heatwaves, little is known about cold‐water extremes, referred to as lake cold spells. Here, we employ a numerical lake model to investigate global lake cold spell dynamics from 1979 to 2100. From 1979 to 2022, lake cold spells have become shorter‐lasting and weaker. Change rates in the occurrence (i.e., total days) and intensity of lake cold spells are −3.96 days decade−1 and 0.26°C decade−1, respectively. In Europe, the decline in lake cold spells is due to increases in the mean of surface water temperatures, whereas in North America, the reduction is due to decreases in the variance of surface water temperature. In the future, lake cold spells will shorten by 19.3 days and weaken by 1.97°C in the end of the 21st century under the high‐greenhouse‐gas‐emission scenario, underscoring a shift in the surface temperature regime that may have an important influence on lake ecosystems. Plain Language Summary: There is a universal warming trend in lake surface water temperature (LSWT), which is causing an increase in lake heatwaves. However, it is unclear how extreme cold‐water events (i.e., lake cold spells) varies in the worldwide. Here, we found that lake cold spells have shortened and weakened in recent decades, and this trajectory are expected to continue under the influence of climate change. We discovered that the statistical features of LSWT, specifically the mean and variance, have a great influence in driving changes in lake cold spells. Our research provides a systematic view of cold extremes in lake surface water, highlighting the vulnerability of lake ecosystems to climate change. Key Points: Lake cold spells have declined from 1979 to 2022Mean and variance of surface water temperature drive the changes in lake cold spellsContinued shortening and weakening of lake cold spells are expected in the late of 21st century [ABSTRACT FROM AUTHOR]