Why future hurricanes could bring flooding to millions more Americans
Hurricanes are bringing more rainfall than ever before, mainly due to climate change. With oceans absorbing an estimated 91% of the excess heat caused by greenhouse gas emissions, waters are warming at unprecedented levels. Hotter oceans provide energy that enables hurricanes to rapidly intensify and drop extreme amounts of precipitation.
Traditionally, hurricanes are examined by wind speed. The current hurricane warning system, known as the Saffir-Simpson Hurricane Scale, is a 1 to 5 rating that is based upon the maximum sustained wind of a storm. The scale is best used to predict property damage related to wind, but the scale does little to inform the public about potential flooding.
Warmer oceans can help hurricanes rapidly intensify as they approach land, meaning the wind can increase more than 35 mph in a 24-hour period, turning that storm from a Category 1 into something much higher. But hot oceans also feed moisture into the atmosphere, which increases the amount of precipitation that accompanies a storm. Current scientific modeling predicts rainfall rates will increase between 10-15% on average for most storms as the Earth approaches 2 degrees Celsius of warming.
Already, many hurricanes that have made landfall in the United States in the past 10 years have demonstrated rapid intensification and extreme levels of precipitation that have devastated communities. Hurricanes Harvey, Florence, and Ida produced catastrophic rainfall that caused record-level flooding, mainly inland:
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