Cumulative intensity heatwave index as assessment tool of the climate change effects on shallow lakes

Abstract

Although lakes represent only 0.26% of the total freshwater on Earth, society makes use of them for essential environmental services, such as public supply and irrigation. To maintain these services, one of the parameters typically used in lake management is water temperature, as it drives its physical, chemical and biological processes. To explore the effects of climate change in Lake Mangueira, a subtropical coastal shallow lake, we assess the occurrence of heatwaves from lake surface water temperature data and from cumulative intensity index, which associates the duration of heatwaves with their respective mean intensity. The Air2Water water temperature estimation model was calibrated using an observed time-series with daily air temperature data, and with water surface temperature data obtained via remote sensing. Based on climate projections obtained via 26 global climate models, Air2Water was used to generate a time-series of water temperature in the historical period and in the future scenarios SSP1-2.6, SSP2-4.5, and SSP5-8.5. We find that at least 75% of the projections indicate lake heatwaves with a cumulative intensity higher than 50°C day in the SSP5-8.5 scenario, against 18°C day of the historical period. Even in the least critical future scenario (SSP1-2.6), 75% of the projected average cumulative intensity values equal or exceed all the projections of the historical period. These findings indicate a particularly worrying change in the thermal dynamics of Lake Mangueira, which will be subject to more intense and/or longer-lasting heatwaves, implying potentially serious effects on the aquatic communities living in this environment. The cumulative intensity index can thus be used to monitoring extreme events in these ecosystems, aiming to manage them properly.

Keywords: Aquatic ecosystems, lake heatwaves, limnology.