The Paroxysmal Precipitation of the Desert: Flash Floods in the Southwestern United States. Issue 12 (6th December 2019)

• Record Type: Journal Article
• Authors: Smith, James A.; Baeck, Mary Lynn; Yang, Long; Signell, Julia; Morin, Efrat; Goodrich, David C.
• Is Part Of: Water resources research. Volume 55:Issue 12(2019)
• Page Start: 10218
• Page End: 10247
• Publication Date: 2019-12-06
• Subjects: Hydrology -- Periodicals; 333.91
• DOI: 10.1029/2019WR025480
• Languages: English
• ISSNs: 0043-1397

Abstract

Abstract: The 14 September 2015 Hildale, Utah, storm resulted in 20 flash flood fatalities, making it the most deadly natural disaster in Utah history; it is the quintessential example of the "paroxysmal precipitation of the desert". The measured peak discharge from Maxwell Canyon at a drainage area of 5.3 km 2 was 266 m 3 /s, a value that exceeds envelope curve peaks for Utah. The 14 September 2015 flash flood reflects features common to other major flash flood events in the region, as well as unique features. The flood was produced by a hailstorm that was moving rapidly from southwest to northeast and intensified as it interacted with complex terrain. Polarimetric radar observations show that the storm exhibited striking temporal variability, with the Maxwell Canyon tributary of Short Creek and a small portion of the East Fork Virgin River basin experiencing extreme precipitation. Periods of extreme rainfall rates for the 14 September 2015 storm are characterized by K D P signatures of extreme rainfall in polarimetric radar measurements. Similar K D P signatures characterized multiple storms that have produced record and near‐record flood peaks in Colorado Plateau watersheds. The climatology of monsoon thunderstorms that produce flash floods exhibits striking spatial heterogeneities in storm occurrence and motion. The hydroclimatology of flash flooding in arid/semiarid watersheds of the southwestern United States exhibits relatively weak dependence on drainage basin area. Large flood peaks over a broad range of basin scales can be produced by small thunderstorms like the 14 September 2015 Hildale Storm, which pass close to the outlet. Key Points: The 14 September 2015 Hildale storm was a hailstorm that produced catastrophic flooding in southern Utah The climatology of monsoon thunderstorms that produce flash floods in the southwestern United States exhibits large spatial heterogeneity Record flood peaks over a wide range of basin scales are produced by "small, " monsoon storms that pass close to the basin outlet