Hourly rainfall intensity continues to increase
AUSTIN (KXAN) -- Heavy downpours are becoming more intense in the United States as climate change supercharges the water cycle, leading to an increase in rainfall rates.
Rainfall rates are a measurement of the amount of rain that falls in a given area in a specific time, and it is calculated in inches.
Grade-school students often learn about the water cycle in their science/weather classes. The water cycle involves the continuous movement of water on, above and below the surface of the Earth, and there are four stages—evaporation, condensation, precipitation, and collection.
It's the precipitation part of the cycle that our partners at Climate Central have been studying since 1970.
Hourly rainfall rates have been rising in much of the United States over time, and Climate Central studied 144 cities, including Austin, to see how the rainfall rates have changed.
The calculation used to determine the change is the total annual rainfall divided by the total hours of rainfall each year.
Climate Central determined the increase in the hourly rainfall intensity shows a rise in the hourly rain rate, or more rain falling per hour, but does this happen every time it rains? Of course, not. Much of the rain last week (March 24 to 28) was light in intensity.
The calculation revealed this statistic: For every 1° the atmosphere will get greedier by holding on to 4% more moisture, leading to the potential of heavier rainfall events.
For 144 U.S. cities, Climate Central found 88% (126 of 144) have seen hourly rainfall rates increase since 1970. The average increase is 15%.
In Austin, the increase was a little higher than the national average. Our city saw a 19% increase in these heavy rain events. It ranked 94 of the 144 cities (65%) with an increase in rain intensity of 10% or higher.
Wichita, Kansas, is the city with the highest rain rate increase at 38%. El Paso tied for second at 37% with Fairbanks, AK, and Reno, NV. San Antonio tied for fifth at 29% with Sioux City, IA.
What happens when heavy rains occur? Flash flooding and flooding in general. The National Weather Service's study of storm reports shows that floods have cost just under $160 billion and taken the lives of at least 2000 between 1996 and 2020.
It is projected that as we go forward in our warming climate that the frequency and the heavy rain intensities will continue to increase.
Finally, it should be noted that May is Central Texas's wettest month with a monthly total of 5.04". We see fewer cold fronts in May, allowing for a significant increase in moisture from the Gulf of Mexico.