Abstract
An emerging concern for lake ecosystems is the occurrence of compound extreme events i.e. situations where multiple within-lake extremes occur simultaneously. Of particular concern are the co-occurrence of lake heatwaves (anomalously warm temperatures) and high chlorophyll-a extremes, two important variables that influence the functioning of aquatic ecosystems. Here, using satellite observations, we provide the first assessment of univariate and compound extreme events in lakes worldwide. Our analysis suggests that the intensity of lake heatwaves and high chlorophyll-a extremes differ across lakes and are influenced primarily by the annual range in surface water temperature and chlorophyll-a concentrations. The intensity of lake heatwaves is even greater in smaller lakes and in those that are shallow and experience cooler average temperatures. Our analysis also suggests that, in most of the studied lakes, compound extremes occur more often than would be assumed from the product of their independent probabilities. We anticipate compound extreme events to have more severe impacts on lake ecosystems than those previously reported due to the occurrence of univariate extremes.
Highlights
Climatic extremes, in particular storms, heatwaves and droughts are becoming more frequent, a trend that has been linked to directional climate change (Fischer and Knutti 2015, Seneviratne et al 2021)
Our analysis suggests that the intensity of lake heatwaves and high chlorophyll-a extremes differ across lakes and are influenced primarily by the annual range in surface water temperature and chlorophyll-a concentrations
Our analysis suggests that the average intensity of these univariate extremes vary considerably across the global lake distribution
Summary
In particular storms, heatwaves and droughts are becoming more frequent, a trend that has been linked to directional climate change (Fischer and Knutti 2015, Seneviratne et al 2021). These extreme events frequently, but not exclusively, result in extreme within-lake conditions (Perga et al 2018, Stockwell et al 2020, Jennings et al 2021), including the occurrence of lake heatwaves (Woolway et al 2021a, 2021b), more severe hypoxia (Jankowski et al 2006), and the occurrence of high phytoplankton biomass (Jöhnk et al 2008, Posch et al 2012, Mastrotheodoros et al 2020). Given the expected increase in extremes across much of the globe with climate change, an evaluation of compound extreme events in lakes has taken on new and critical importance
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