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

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 the Coupled Model Intercomparison Project Phase 6 (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 South Africa (SAF), North Africa (NAF), and South America (SAM) but earlier over South Asia (SAS) and Australia (AUS) in a warmer climate. The projected early RODs in AUS are more pronounced at 2°C GWL under the SSP5–8.5 scenario. On the other hand, early RCDs are projected over SAM and East Asia, while late RCDs are projected over NAF 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 SAM, NAF, and SAF monsoon regions. The findings underscore the urgent need to mitigate global warming.