Study Confirms Higher Rainfall Rates Across U.S.

A new analysis is warning that a warming atmosphere is responsible for the higher incidence of flooding and the resulting damage. Here is a deeper look at what the data revealed.

Data Confirms Higher Hourly Rainfall Rates

A study that looked at 60 years of rainfall records across the U.S. paints an interesting picture. While precipitation totals have remained steady over the last decade, heavy downpours and higher hourly rates of rain are increasing the threats of flooding. So, while it is not raining more, the moisture that does fall is coming down faster and heavier.

The data was extracted from a vast database, looking at rainfall across 44 distinct climate zones in the U.S. The national composite of the dozens of zones did not show any upward trend in annual precipitation rates. However, hourly rainfall rates and heavy-rainfall days both have increased since the middle of the 20th century. The largest increases have happened over the past three decades.

The trend toward higher rainfall rates without the addition of overall greater participation totals increases the risk of flooding events exponentially. Rain that is spread out over time is not as likely to overwhelm storm drainage systems, culverts, and waterways.

The researchers looked at daily totals from precipitation events ranging from light rain showers to extreme downpours, totaling how many hours brought more than an inch of rain annually. What the researchers found was a steady increase in rainfall intensity.

The instances of days with at least three-quarters of an inch of rain have jumped by approximately 10% over the last three decades, despite overall national rainfall totals remaining flat. In addition, daily rainfall events of 4 inches or more have doubled since the 1960s. The hours each year featuring rainfall of one inch or more have tripled since 1950. Lastly, daily rain events of at least four inches have also doubled since the 1960s.