Impacts of 1.5°C and 2.0°C Global Warming on the Onset, Cessation, and Length of the Rainy Season in Global Land Monsoon Regions

Abstract The onset, cessation, and length of the rainy season are crucial for global water resources, agricultural practices, and food security. However, the response of precipitation seasonality to global warming remains uncertain. In this study, we analyze how global warming levels (GWLs) of 1.5°C and 2°C could affect the timing of rainfall onset (RODs), rainfall cessation (RCDs), and the overall duration of the rainy season (LRS) over global land monsoon (GLM) regions using simulations from CMIP6 under the SSP2-4.5 and SSP5-8.5 scenarios. With high model consensus, our results reveal that RODs are projected to occur later over Southern Africa, North Africa, and South America, but earlier over South Asia and Australia, in a warmer climate. The projected early RODs in Australia are more pronounced at the 2°C GWL under SSP5-8.5. On the other hand, early RCDs are projected over South America and East Asia, while late RCDs are projected over North Africa, with high inter-model agreement. These changes are associated with a future decrease in LRS in most GLM regions. Additionally, we found that continuous warming over 1.5°C will further reduce the length of the rainy season, especially over the South America, North Africa, and Southern Africa monsoon regions. The findings underscore the urgent need to mitigate global warming.