The effect of rising mean sea levels will be felt most profoundly during extreme storm conditions when strong winds and falling pressure bring about a temporary and localised increase in sea level known as a storm surge. Storm surges occurring on higher mean sea levels will enable inundation and damaging waves to penetrate further inland increasing flooding, erosion and the subsequent detrimental impacts on built infrastructure and natural ecosystems. In the tropics storm surges are caused by tropical cyclones while elsewhere mid-latitude storms and their associated cold fronts are the main cause of storm surges.
Sea level rise also increases the vulnerability of coastal areas to flooding during storms for several reasons. First, a given storm surge from a hurricane or northeaster builds on top of a higher base of water. Considering only this effect, it is estimated that existing development in the U.S. Coastal Zone would experience a 36-58 percent increase in annual damages for a 30 cm rise in sea level, and a 102-200 percent increase for a 1 m rise. Shore erosion also increases vulnerability to storms, by removing the beaches and dunes that would otherwise protect coastal property from storm waves (FEMA 2000). Sea level rise also increases coastal flooding from rainstorms, because low areas drain more slowly as sea level rises.
Other impacts of climate change may further enhance or mitigate coastal flooding. Flooding from rainstorms may become worse if higher temperatures lead to increasing rainfall intensity during severe storms. An increase in the intensity of tropical storms would increase flood and wind damages.