POURING IT ON: How Climate Change Intensifies Heavy Rain Events

https://www.climatecentral.org/news/report-pouring-it-on-climate-change-intensifies-heavy-rain-events

May 15, 2019

In the spring of 2019, floodwaters overwhelmed levees across the Midwest, drenching towns and causing billions of dollars in infrastructure and crop damage. Record downpours in Tennessee provoked a state of emergency and led to mudslides. In California, heavy precipitation damaged thousands of buildings. Extreme rain events have devastated communities around the nation — and the frequency and severity of such events are expected to worsen in a warming world.

Human-caused climate change intensifies the heaviest downpours. More than 70% of the planet’s surface is water, and as the world warms, more water evaporates from oceans, lakes, and soils. Every 1°F rise also allows the atmosphere to hold 4% more water vapor. So when weather patterns lead to heavy rain, there is even more moisture available for stronger downpours, increasing the risk and severity of flooding.

Floods often happen on the rainiest day of the year — the single calendar day with the most precipitation. Climate Central tracked how these wet days are trending over time, analyzing data for 244 cities around the country. In most areas, rainfall extremes have intensified as the climate has warmed.

•••••

In addition to getting stronger, extreme downpours are happening more frequently than in the past. In 80% of the cities analyzed, the top 1% of rain events have been recorded disproportionately recently.

•••••

Finally, most cities have recently observed more storms with an inch of rain or more, causing threats of flooding to spike upward. The national frequency of 1”, 2”, and 3” storms has markedly increased since 1950.

•••••

The U.S. government’s Climate Science Special Report provides a clear example. If greenhouse emissions continue unchecked, the frequency of a once-in-five-years rain event could increase two-to-threefold by late century. But if the world makes significant emissions cuts — roughly in line with the pledges from the Paris Agreement — the increase in frequency could be cut in half. In a waterlogged world, that difference would be critical.