Rarest rainfall events have greatest relative increase under climate change

Future rainfall extremes are expected to increase due to global warming based on both theoretical considerations and climate model outcomes. Common (yearly) extremes and rare (decennial or centennial) extremes may be affected differently. Here we show that the rarer the event, the more it is relatively expected to increase in a future climate. For the mitigation scenario SSP1-2.6 and the high emission scenario SSP5-8.5 daily land rainfall extremes will increase by 10.5 % and 28.2 %, respectively, for yearly events and by 13.5 % and 38.3, respectively, for 100-year events by the end of this century. These numbers are based on frequency and extreme value analyses applied to 25 different CMIP6 earth system models, weighted for independence and performance. The findings are consistent and statistically significant across all 25 earth system models, 102 different model runs, and four different possible climate futures. Our results show distinct regional differences, with some regions disproportionally affected relative to others. This has important implications for engineering design standards, which need to be raised more for systems designed for the rarest events.