New research at Maynooth University’s ICARUS Climate Research Centre shows a 40% rise in hurricane rainfall rate and 140% increase in total rainfall over land when ocean temperatures in the North Atlantic are 1°C warmer than normal.
The study, published this week in the peer-reviewed scientific journal Environmental Research Communications, provides an analysis of how hurricane rainfall rate and total rainfall increase for a 1-degree rise in ocean temperatures in the main hurricane development region of the North Atlantic, during the period 1998 – 2017.
In recent years, there have been increasing losses from freshwater flooding associated with United States landfalling hurricanes. Hurricanes produce intense rainfall which causes flash flooding, and this study looks at the impact across 9 US States. In 2017 Hurricane Harvey caused more than $100bn mostly flood-related damages in the US and in 2022 Hurricane Ian caused flood losses estimated at between $8-18bn of which, around 50% are uninsured.
The lead author of the paper, Dr Samantha Hallam, of the ICARUS Climate Research Centre at Maynooth University in Ireland, and the National Oceanography Centre, UK, said:
“In this study, we find a 40% rise in tropical cyclone rainfall rate and 140% increase in total rainfall over land when ocean temperatures are 1°C warmer than normal in the main hurricane development region in the North Atlantic, between 1998-2017.”
“The 40% rise in tropical cyclone rainfall rate over land contrasts with the 6% increase in the rainfall rate observed over the Atlantic Ocean and appears to indicate both a thermo-dynamic and a dynamic response to anomalously warm ocean temperatures, meaning hurricanes are making landfall with higher windspeeds when ocean temperatures are warmer.”
The 140% increase in total rainfall, for a 1-degree rise in ocean temperatures, is not only linked to the thermodynamic response associated with the Clausius-Clapeyron relationship (which says that rainfall intensity increases by about 7% for each degree of warming), but to the increase in windspeed and the number of landfalling tracks which also rises with warmer ocean temperatures as highlighted in the study.
Overall, this research provides useful insights for seasonal to decadal flood prediction from Atlantic tropical cyclones (hurricanes) and the associated flood risk, helpful for homeowners, policymakers and insurers.
These findings are the result of a statistical analysis of the IBTrACS and TRMM datasets. The research was supported by the Marine Institute and funded by the Irish Government under the JPI Climate and JPI Ocean joint call and the Natural Environmental Research Council, and involved collaboration between ICARUS Climate Research Centre at Maynooth University in Ireland, University of Reading, University of Southampton, UK, and National Oceanography Centre, UK.