Cumulative intensity heatwave index as an assessment tool for climate change effects on shallow lakes

Resumen

Although lakes represent only 0.26% of the total freshwater on Earth, they provide essential environmental services, such as public water supply and irrigation. Water temperature, which drives the lake’s physical, chemical, and biological processes, is a parameter typically used for lake management plans. To explore the effects of climate change on Lake Mangueira, a subtropical coastal shallow lake, we assessed the cumulative intensity index, which links heatwave duration to mean intensity. The Air2Water model was calibrated using time series of observed daily air temperature data and water surface temperature data obtained via remote sensing. Based on climate projections obtained from 26 global climate models, the Air2Water model was used to generate water temperature time series for a historical period and future scenarios, including SSP1-2.6, SSP2-4.5, and SSP5-8.5. We found that at least 75% of the projections indicated lake heatwaves with a cumulative intensity exceeding 50 °C days under the SSP5-8.5 scenario, compared to 18 °C days in the historical period. Even in the least severe future scenario (SSP1-2.6), 75% of the projected average cumulative intensities were equal to or exceeded every value from the historical period. These findings highlight a concerning shift in the thermal dynamics of Lake Mangueira. The lake is expected to experience more intense and/or longer-lasting heatwaves that have the potential to significantly affect its aquatic communities. The cumulative intensity index can therefore be used to monitor extreme events in these ecosystems, which will help to properly manage them.