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Rainfall Thresholds for Flow Generation in Desert Ephemeral Streams
Author(s) -
Kampf Stephanie K.,
Faulconer Joshua,
Shaw Jeremy R.,
Lefsky Michael,
Wagenbrenner Joseph W.,
Cooper David J.
Publication year - 2018
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2018wr023714
Subject(s) - hydrology (agriculture) , streamflow , streams , ephemeral key , surface runoff , environmental science , watershed , arid , drainage basin , drainage , geology , geography , ecology , computer network , paleontology , geotechnical engineering , cartography , machine learning , computer science , biology
Rainfall 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 10 2 km 2 . 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 km 2 ) 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‐km 2 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.