Tom Knutson, senior scientist at NOAA’s Geophysical Fluid Dynamics Laboratory, is a leading scientist on hurricanes and climate change. He notes that “even if hurricanes themselves don’t change [due to climate change], the flooding from storm surge events will be made worse by sea level rise.” In addition, he says models show increases in a hurricane’s rainfall rate by 2100. This means that hurricanes are likely to cause more intense rain when they come ashore.
Scientists have long predicted that climate change would increase extreme rainfall events. In a warmer world, there is simply more moisture in the air in the form of gaseous water vapor. Think of heating up a pot of water on the stove. Once the liquid water becomes hot enough, it boils and creates steam (or hot water vapor). This process is called “evaporation,” or when a liquid changes to a gas.
A similar process happens at Earth’s surface. As surface temperatures rise, more liquid water evaporates from the land and ocean. Evaporation adds moisture to the air. How much water vapor the air can hold is based on its temperature. Warmer air temperatures can hold more water vapor. The increased moisture in the air leads to more intense rainfall, especially during extreme events.
In a hurricane, spiraling winds draw moist air toward the center, fueling the towering thunderstorms that surround it. As the air continues to warm due to climate change, hurricanes can hold more water vapor, producing more intense rainfall rates in a storm.
Moreover, according to Knutson, most models show that climate change brings a slight increase in hurricane wind intensity. This change is likely related to warming ocean temperatures and more moisture in the air, both of which fuel hurricanes. While most models show either no change or a decrease in hurricane frequency in a warmer climate, a greater proportion of the storms that form will reach very intense (Category 4 or 5) levels. In other words, while there may be fewer storms, the ones that form have a greater chance of becoming stronger