Climate Matters: A warmer climate is also a wetter one

It's early May, but we're still holding on to April showers in Mid-Missouri, with several rounds of heavy rain on the way.

Rain is falling more heavily as the climate changes, especially in the Midwest. According to a Climate Central analysis of 144 U.S. cities, about 90% have recorded an increase in hourly rainfall intensity. These cities have seen hourly rainfall rates rise by an average of 15% over the past half-century.

"Rain is falling harder than it used to," says Shel Winkley, a meteorologist at Climate Central. "And while the rainfall rate has increased in every U.S. region, the largest increase is happening among cities in the Upper Midwest."

This is because warmer air can hold more moisture. In an idealized scenario, for every 1 °F increase in temperature, the atmosphere can hold 4% more moisture. But in reality, storms often produce much more.

St. Louis is a great example. The average temperature in St. Louis has risen by 4.4 °F since 1970, which should equate to an 18% increase in rainfall. However, average rainfall intensity has increased by roughly 23% in St. Louis over the same period, several points above the idealized rate and higher than the nation's average. That means a storm that would have produced 2 inches of rain decades ago would now drop almost 2 and a half inches of rain.

As climate change intensifies the water cycle, the wettest days are also getting wetter. The top 1% of wettest days in the Upper Midwest are now seeing 45% more precipitation compared to the 1960s.

Increasing rainfall also increases the risk of flooding, which is already the deadliest severe weather threat. And when heavy rains hit suddenly after a long drought, it can make the situation worse.

"Even drier parts of the country are seeing heavier downpours when the rain does fall," Shel says. "These intense bursts leave little time to act, threatening homes, infrastructures, and communities, risks that tend to fall hardest on the rural areas and across the South."

As the world continues to burn fossil fuels and drive up temperatures, rainfall will continue to get heavier. "Looking ahead with continued warming, 85% of over 3000 U.S. counties are projected to see at least a 10% increase in precipitation during their heaviest rain events."