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Rainfall thresholds for flow generation in desert ephemeral streamsAuthor(s): Stephanie K. Kampf; Joshua Faulconer; Jeremy R. Shaw; Michael Lefsky; Joseph W. Wagenbrenner; David J. Cooper
Source: Water Resources Research. 54: 9935-9950
Publication Series: Scientific Journal (JRNL)
Station: Pacific Southwest Research Station
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DescriptionRainfall thresholds for streamflow generation are commonly mentioned in the literature, but studies rarely include methods for quantifying and comparing thresholds. This paper quantifies thresholds in ephemeral streams and evaluates how they are affected by rainfall and watershed properties. The study sites are in southern Arizona, USA; one is hyperarid and the other is semiarid. At both sites rainfall and streamflow were monitored in watersheds ranging from 10−3 to 102 km2. Streams flowed an average of 0–5 times per year in hyperarid watersheds and 3–11 times per year in semiarid watersheds. Although hyperarid sites had fewer flow events, their flow frequency (fraction of rain events causing flow) was higher than in semiarid sites for small (<1 km2) watersheds. At both locations flow frequency decreased with drainage area, but the decrease was steeper in hyperarid watersheds. Watershed mean 60‐min intensity thresholds ranged from 3–13 mm/hr in hyperarid watersheds and 7–16 mm/hr in semiarid watersheds. Higher runoff thresholds and lower flow frequencies in small semiarid watersheds likely relate to greater ground cover and soil development compared to the desert pavement and bedrock surfaces in hyperarid sites. The choice of rain data strongly influenced threshold values; single rain gauges were only adequate for threshold prediction in <1‐km2 watersheds, and incomplete rainfall data led to increases in thresholds with drainage area. We recommend using mean rainfall intensity over the drainage area for threshold analysis because this reduces apparent scale dependence in thresholds caused by incomplete rainfall information.
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CitationKampf, Stephanie K.; Faulconer, Joshua; Shaw, Jeremy R.; Lefsky, Michael; Wagenbrenner, Joseph W.; Cooper, David J. 2018. Rainfall thresholds for flow generation in desert ephemeral streams. Water Resources Research. 54: 9935-9950. https://doi.org/10.1029/2018WR023714.
Keywordsephemeral stream, rainfall‐runoff threshold, radar precipitation, desert hydrology, desert pavement, overland flow
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