Exploring warm extremes in South America: insights into regional climate change projections through dry-bulb and wet-bulb temperatures

Abstract

This study addresses a regional research gap by analyzing summertime wet-bulb temperature (Tw) projections in South America (SA) and their implications for heatwaves in central-east Argentina (CEA). Tw emerges as a relevant variable to address the potential impact of humid and warm extremes under future climate conditions, while allowing comparison with more classical analyses based on dry-bulb temperature indices. The analyses presented in this work are based on outputs from Regional Climate Models provided by CORDEX (COordinated Regional climate Downscaling EXperiment) South America database. Tw increases in all SA stem from rising temperature and specific humidity at lower atmospheric layers. Projected Tw rise surpasses the expected maximum dry-bulb temperature (Tmax) increase across most of SA, exhibiting pronounced disparities in subtropical areas and intensifying further in CEA towards the century’s end. Projected trends in Tw and minimum dry-bulb temperature (Tmin) show similarities across SA, except for a limited area within CEA where relatively larger Tw increases are expected. The frequency and intensity of heat extremes are also anticipated to increase in the coming years in SA. Noteworthy findings encompass projected increases in hot days, hot nights, and wet days, with the tropical region standing out for its pronounced projections. Remarkably, the number of wet days would rise significantly, followed by less prominent increases in the number of hot nights and days. Moreover, heightened persistence is expected for wet days compared to hot days and nights. A bivariate statistical analysis of heatwave projections in CEA reveals a transition towards warmer and more humid spells. This underscores the critical need to integrate air humidity conditions for accurate assessments of future health risks. Despite inherent uncertainties in climate change projections, consensus emerges on the direction of the expected changes, as well as on the urgency of limiting greenhouse gas emissions to mitigate the imminent threat of humid heatwaves in CEA.