Ocean warming will create increased hurricane rain risk

The world has been told to brace for more intense hurricane and cyclones with a new study finding a 1°C increase in ocean temperatures will have a significant effect on the rate of rainfall.

The study by Ireland’s 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.

Researchers said the study 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 nine US States. In 2017 Hurricane Harvey caused more than $100 billion mostly flood related damages in the US  and in 2022 Hurricane Ian caused flood losses estimated at between $8 bilion-18 billion of which, around 50% are uninsured.

Lead author of the paper, Dr Samantha Hallam, of the ICARUS Climate Research Centre at Maynooth University, and the National Oceanography Centre, UK, explained: “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 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, policy makers and insurers,” the study explained.

“Research undertaken at ICARUS aims to advance fundamental understanding of past, present and future climate variability and change, and to provide cutting edge analysis of future impacts, vulnerabilities and adaptation in line with strategic national and international priorities,” added Hallam.