Daily data are critical to our understanding of precipitation, but its intermittent nature highlights the need to quantify other characteristics such as frequency, intensity, and duration, which do not operate at the daily scale ( Trenberth and Zhang 2017). These variables are condensed into one quantity and summed over a day, month, season, or year to define precipitation, primarily because most precipitation data are recorded daily ( Zolina et al. However, using accumulation alone omits a large portion of the precipitation story, such as cause, type, duration, and intensity. Total accumulation, which represents an aggregation of rainfall characteristics, is often used to quantify precipitation and is a vital metric for agriculture, freshwater resources, and water availability. This inherent variability has a large effect on the hydrologic cycle, and small shifts in precipitation totals, intensity, and duration impact runoff, soil moisture, and crop yields in the region ( Karl and Riebsame 1989).
For example, in 2007 an extreme drought struck parts of Georgia, Alabama, eastern Tennessee, and the Carolinas, followed by excessive rainfall and flooding in roughly the same area in 2009, both of which caused catastrophic economic loss ( Manuel 2008 Maxwell and Soulé 2009 Gotvald and McCallum 2010). Precipitation across the southeastern United States (hereafter SeUS) varies substantially from year to year.
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. Decreases in PH during spring were contained to Georgia and South Carolina and were accompanied by a decrease in accumulation. PH significantly decreased across South Carolina, Georgia, and northern Florida, mainly due to significant decreases in winter (DJF) and spring (MAM). Geographically, heavy hourly events are more frequent along the Gulf Coast and decrease inland. It seems hourly events are becoming heavier on average, while the duration of the average precipitation event is decreasing. 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.
The average duration of precipitation events decreased at 82% (41/50) of the stations. Results indicate 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).
#Precipitation totals by state series
This research introduces a climatology of hourly precipitation characteristics, investigates trends in precipitation hours (PH) and hourly accumulation, and uses four different time series to determine if precipitation intensity is changing across the southeastern United States from 1960 to 2017.
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