Rising temperatures increase evaporation from the ocean, which increases the amount of water vapor in the atmosphere. This additional water vapor can be pulled into large storm systems, leading to increased rainfall and even flooding.
Storms also organize the winds around them. The large-scale circulation of winds in a storm influences how much moisture comes in, how much it spirals upward and cools, and how much falls out as precipitation. And changes in the winds that steer storms can alter the storms’ tracks, potentially moving storms that would otherwise stay out at sea closer to coastal communities, or sending a storm from one region to another.
Some storms, like hurricanes and nor’easters, also draw energy from the temperature difference between the ocean surface and the cooler atmosphere above. When ocean waters are warmer, hurricanes and nor’easters can potentially grow larger, last longer and dump more rain.
The influence of warming oceans is compounded by other aspects of climate change. Increased rainfall rates mean a given amount of rain falls in a shorter amount of time. So even if the total rainfall of a storm is not greatly increased, more rain coming down all at once can still cause flooding.
On top of this, sea levels are rising as a result of the thermal expansion of warming ocean water and runoff from land-based ice melt, which can contribute to flooding from coastal storms.
