Tropical cyclone rainfall changes in a warmer climate

Heavy precipitation and flooding associated with tropical cyclones (TCs) are responsible for a large number of fatalities and economic damage worldwide. Due to the societal and economic relevance of this hazard, studies have focused on the potential changes in heavy rainfall associated with TCs in a warmer climate. Despite the overall agreement about the tendency of TC rainfall to increase with greenhouse warming, the uncertainty of the projected changes is large, ranging from 3 to 37 %. Models project an increase in rainfall over land, both in terms of average and extremes, and a large spatial variability is associated with changes in projected rainfall amount. The goal of this study is to quantify the contribution of landfalling TCs to rainfall at different latitudes, as well as its dependence on different idealized climate change scenarios. Possible changes in the intensity of rainfall events associated with TCs are investigated under idealized forcing scenarios, with a special focus on landfalling storms. A new set of experiments designed within the US CLIVAR Hurricane Working Group allows disentangling the relative role of changes in atmospheric carbon dioxide from that played by sea surface temperature (SST) in changing the amount of rainfall associated with TCs in a warmer world. Compared to the present-day simulation, we found an increase in TC rainfall under the scenarios involving SST increases. On the other hand, in a CO2 doubling-only scenario, the changes in TC rainfall are small and we found that, on average, TC rainfall tends to decrease compared to the present-day climate. The results of this study highlight the contribution of landfalling TCs to the projected increase in the rainfall changes affecting the tropical coastal regions. Scenarios involving SST increases project a TC rainfall strengthening more evident over land than over ocean. This is linked to the increased lifting effect on the landfalling TCs, induced by a more moist air at low levels.