Climatology and Trends in Hourly Precipitation for the Southeast United States

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Investigator(s): Barry Keim, Alan Black, Vincent Brown
Research Dates: 2019 - 2021
Affiliate Organization(s): Louisiana State University • Southern Illinois University at Edwardsville

This research introduceds a climatology of hourly precipitation characteristics, investigated trends in precipitation hours (PH) and hourly accumulation, and used four different time series to determine if precipitation intensity is changing across the southeastern United States from 1960 to 2017. Results indicated hourly intensity significantly increased at 44% (22/50) of the stations, accompanied by an increase in average hourly accumulation at 40% of the sites analyzed (20/50). The average duration of precipitation events decreased at 82% (41/50) of the stations. However, the frequency of 90th percentile hourly events and events above station-specific average hourly totals did not show a broad increase similar to hourly intensity. It seems hourly events are becoming heavier on average, while the duration of the average precipitation event is decreasing. Geographically, heavy hourly events are more frequent along the Gulf Coast and decrease inland. PH significantly decreased across South Carolina, Georgia, and northern Florida, mainly due to significant decreases in winter (DJF) and spring (MAM). Decreases in PH during spring were contained to Georgia and South Carolina and were accompanied by a decrease in accumulation. Decreases in PH during winter were more widespread and did not exhibit a broad decrease in accumulation, suggesting winter precipitation across that portion of the region is becoming more intense.

We found an interesting pattern where nearly half the stations in the region observed a slight increase in hourly intensity. Also, parts of the region experienced significant decreases in precipitation frequency in winter and spring (Carolina, Georgia, northern Florida). Finally, a potential systematic bias was found in the HPD related to precipitation even duration.

For the final paper, click here.

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