Evidence of Increased Lake Heatwave Indices in a Subtropical Coastal Shallow Lake Estimated From Climate Change Scenarios

Abstract 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 impacts of climate change scenarios on the structure and functioning of lake systems. Within this context, this study used the concept of lake heatwaves to assess these 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 (1985–2014) and according to three future (2081–2100) scenarios — SSP1-2.6, SSP2-4.5, and SSP5-8.5 — based on data from 26 global climate models (GCMs). The results were expressed in terms of heatwave indices, which were initially proposed for marine environments and have since been applied to lake ecosystems. Most of the projections obtained indicated positive anomalies for all lake heatwave indices, especially for the average duration and cumulative intensity and in the SSP5-8.5 scenario, compared to the historical period. In addition to the total duration, two of the five indices evaluated were presented for each year associated with the historical period and future scenarios. This analysis revealed an increase in the mean values of these indices in the three future scenarios compared to the historical period, again with SSP5-8.5 standing out. Finally, lake heatwaves lasting more than one season were projected for Lake Mangueira, with some projections indicating the permanent occurrence of these extreme events. Properly studying these events is of paramount importance in the management of lake systems and their associated environmental services. Keywords: lake ecosystems, water temperature, modeling, remote sensing, extreme events, climate change.