Climate Change Effects on a Subtropical Coastal Shallow Lake from Heatwave Indexes

Water temperature is a driver of chemical, physical, and biological processes in lake systems. Given that these ecosystems are vulnerable to extreme temperature events, it is crucial to assess the potential effects of climate change on the structure and functioning of lake ecosystems. Thus, this study applied the concept of heatwaves to assess its impacts in Lake Mangueira, a subtropical coastal shallow lake located in the Extreme South of Brazil. The Air2Water model was calibrated and used to estimate daily time-series water temperatures using daily time-series air temperatures as the input. The occurrence of lake heatwaves in Lake Mangueira was assessed over a historical period (1995–2014) and under three future (2081–2100) scenarios (SSP1- 2.6, SSP2-4.5, and SSP5-8.5) based on data from 26 global climate models. The results were expressed in terms of five heatwave indexes, and most of the projections obtained indicated positive anomalies for all lake heatwave indexes, especially for the average duration and cumulative intensity and in the SSP5-8.5 scenario. Analysis of average duration, average intensity, and total duration reveled an increase in the annual mean values for the three future scenarios compared to the historical period, with SSP5-8.5 once again standing out. In addition, lake heatwaves lasting more than one season were observed for Lake Mangueira, with some projections indicating a permanent state of occurrence of these extreme events. Properly studying lake heatwaves is of paramount importance in the management of these ecosystems and their associated environmental services.