AUSTIN (KXAN) — Climate change is playing a critical role in enhancing extreme weather including rainfall patterns, intensity and flooding across the country.

As the globe continues to warm (from greenhouse gas emissions) our atmosphere can hold more and more moisture. The air can hold an extra 4% of moisture for every 1°F of warming. This increased warming is enhancing these intense rainfall and flooding events.

Warmer air holds more moisture

Our partners over at Climate Central analyzed 150 cities in the United States and found that of those 150, 136 of them experienced an increase in rainfall intensity since 1970. This comes out to 91% of the analyzed cities experiencing an increase.

Impacts of increased intensity of rain and downpours:

  • More flash flooding events
  • More landslides
  • Negative impacts to agriculture including crops
  • Damage to infrastructure
  • Exposure to more hazardous debris
  • Displaced contaminants including chemicals and sewage
  • Increased water-borne diseases

Their study shows that even in the driest of locations across the country, short bursts of extreme rainfall are also increasing.

The heaviest rainfall extremes are increasing the most in the Southwest and Central portions of the country. Austin has seen an increase of more than 1 and half hundredths of an inch in average hourly rainfall since 1970.

Simple Hourly Rainfall Intensity Index

Climate Central calculated the ‘Simple Hourly Rainfall Intensity Index’ for each of their analyzed cities. This is the calculation of the total annual rainfall divided by the total annual hours with rainfall.

According to Climate Central, “an increase in the Simple Hourly Rainfall Intensity Index indicates an increase in hourly rainfall intensity”. This means an increase in this value is equal to MORE rain falling in an hour. A decrease in this value is equal to less rainfall in an hour. This is only calculated to include days when rain falls.

Even if a city experiences a decreasing yearly rainfall average, you technically could still see an increasing intensity index.

The average change in the Simple Hourly Rainfall Intensity Index across all 150 locations from 1970 to 2022 was +13%. 

TOP 5 CITIES: Change in Simple Hourly Rainfall Intensity Index (1970-2022)

Fairbanks, Alaska44%
El Paso, Texas41%
Wichita Area, Kan.39%
Reno, Nev.37%
Rapid City, S.D.35%
Change in Simple Hourly Rainfall Intensity Index (1970-2022)
Change in annual average hourly rainfall since 1970

While much of the country saw an increase in rainfall intensity, as much as 61% of the cities saw an increase in hourly rainfall intensity of more than 10%.