When it rains, it pours! This old adage was proven to be true last month. With national weather data dating back to 1895, May 2019 was the second wettest month ever recorded in the contiguous United States. Only May 2015 was wetter.
According to NOAA, an average of 4.41 inches of rain fell across the lower 48 states, which is 1.50 inches above average. Heavy precipitation was reported from the West Coast through the Mid-West, and into parts of the Northeast. Kansas, Nebraska, and Missouri each experienced their wettest May on record.
This relentless rain caused deadly and destructive flooding in several states along the Arkansas, Missouri, and Mississippi Rivers.
While there were a number of factors that contributed to May’s excessive rainfall, including El Nino, climate change also likely played a part. As the National Climate Assessment points out, heavy precipitation events are increasing in both frequency and intensity across the United States as the atmosphere warms.
As greenhouse gases heat the atmosphere, the air is able to hold more water vapor. More specifically, according to the Clausius–Clapeyron relation, for every increase of 1°F, the saturation level of the atmosphere increases by about 4%. In other words, warmer temperatures lead to more evaporation from oceans, rivers, and lakes, and therefore more water vapor is available to condense and fall as precipitation.
Sadly, with our global temperature continuing to rise, experts say we should expect to see more extreme rain and flooding events in the future.