Annual trends in extreme hourly precipitation time series were examined at 50 first-order weather stations across the southeastern United States from 1960 to 2017. Results indicated that the magnitude of annual maximum 1-, 3-, 6-, 12-, and 18-h periods did not broadly change at the sites analyzed; however, the numerical value that defines a (station specific) 90th-percentile hourly accumulation significantly (p ≤ 0.05) increased at 36% (18/50) of the stations. No station had a significant decreasing trend in annual 90th-percentile hourly event magnitude. Stations in Texas observed the largest increase in annual 90th-percentile hourly event magnitude, where parameter estimates showed increases of 0.20%–0.26% per year. Annual average dry-spell duration, defined as the average number of hours between measurable precipitation events, significantly decreased at 18% (9/50) of sites analyzed. Parameter estimates from regression performed on average dry-spell-duration time series showed decreases of roughly 0.11%–0.19% per year for the stations across southern Florida. Six stations across Georgia showed significant decreasing trends in the annual maximum consecutive hourly period with measurable precipitation (duration), demonstrating that the longest precipitation events that occurred at these stations have decreased in duration since 1960.
The numerical value that defines a (station specific) 90th-percentile hourly accumulation significantly (p ≤ 0.05) increased at 36% (18/50) of the stations. Essentially, at some sites, the heaviest hourly events are getting slightly heavier through time.
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