Rainfall disasters under the changing climate: a case study for the Rio de Janeiro mountainous region

Climate change impacts the erosive power of rain, influencing mountainous landscapes’ vulnerability to natural disasters. This study evaluated the spatiotemporal projections of daily rainfall erosivity (Rday), an efficient warning index for rainfall disasters, under climate change. The objectives of this study were to project spatially Rday across the Mountain Region of the Rio de Janeiro State (MRRJ), one of the most vulnerable regions to rainfall disasters in Brazil, and to analyze the frequencies of Rday values throughout the twenty-first century. Two greenhouse gas emission scenarios (RCP 4.5 and 8.5), approximating the current status in South America, and a high-resolution climate model (the HadGEM2-ES physically downscaled to 5 km resolution by the Eta/CPTEC model) were applied to estimate daily rainfall values over the MRRJ. The mapping of the maximum Rday values in 30 years (Rmaxday) showed that the entire MRRJ is highly susceptible to rainfall disasters throughout the twenty-first century, with intensification around 2040–2071. Urban areas, where fatalities have been recorded, have been the most vulnerable due to the high frequency of heavy rainfall. The projections for the twenty-first century indicated that 17 (under RCP4.5) and 15 (under RCP8.5) events like the “mega-disaster” could hit the study region. Thus, public policy efforts should focus on effective stormwater management actions to mitigate the impacts caused by such disastrous events in this century.