Research from the National Oceanography Centre (NOC) and Maynooth University in Ireland has shown a 40% rise in hurricane rainfall rate and a 140% increase in total annual rainfall over land for a 1°C rise in ocean temperatures in the North Atlantic.
The study, published in the peer-reviewed scientific journal Environmental Research Communications, provides an analysis of how hurricane rainfall rate and total annual rainfall change for a 1°C rise in ocean temperatures in the main hurricane development region of the North Atlantic, during the study period 1998 to 2017.
The study was led by Dr Samantha Hallam from Maynooth University, while she was a PhD student at NOC. Dr Hallam said, “In this study, we found a 40% rise in tropical cyclone rainfall rate and 140% increase in total annual 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 a thermos-dynamic and a dynamic response to anomalously warm ocean temperatures, meaning hurricanes are making landfall with higher wind speeds when ocean temperatures are warmer.”
The research found that the 140% increase in total annual rainfall, for a 1°C 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 wind speed and the number of landfalling tracks, which also rises with warmer ocean temperatures as highlighted in the study.
Dr Joel Hirschi, associate head of marine systems modeling at NOC and a senior author on the study, said, “Through this study, we’re confident that the connection between ocean temperatures and rainfall will help improve hurricane forecasts, which will prove a vital resource for vulnerable areas that suffer costly flood-related damages during intense hurricane seasons.”
Overall, this research provides useful insights for seasonal to decadal flood prediction from Atlantic tropical cyclones (hurricanes) and the associated flood risk, which is helpful for homeowners, policymakers and insurers.
These findings are the result of a statistical analysis of IBTrACS and TRMM data sets. 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, the National Oceanography Centre at the University of Southampton, and University of Reading.
In recent years, there have been increasing losses from freshwater flooding associated with US 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 US$100bn of mostly flood-related damages in the USA. In 2022, Hurricane Ian caused flood losses estimated at between US$8-18bn of which, around 50% are uninsured.