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Dec 2020

Winter Inputs Buffer Streamflow Sensitivity to Snowpack Losses in the Salt River Watershed in the Lo

Marcos D. Robles, John C. Hammond, Stephanie K. Kampf, Joel A. Biederman and Eleonora M. C. Demaria
Arizona, Colorado River Basin
Climate Change
Forest, Riparian-aquatic
USGS
Abstract

Recent streamflow declines in the Upper Colorado River Basin raise concerns about the sensitivity of water supply for 40 million people to rising temperatures. Yet, other studies in western US river basins present a paradox: streamflow has not consistently declined with warming and snow loss. A potential explanation for this lack of consistency is warming-induced production of winter runoff when potential evaporative losses are low. This mechanism is more likely in basins at lower elevations or latitudes with relatively warm winter temperatures and intermittent snowpacks. We test whether this accounts for streamflow patterns in the Salt River and its tributaries, which is a sub-basin in the Lower Colorado River Basin (LCRB). Despite significant warming from 1968–2011 and snow loss in many of the Salt basins, annual and seasonal streamflow did not decline. Between 25% and 50% of annual streamflow is generated in winter when runoff ratios are generally higher and potential evapotranspiration losses are one-third of potential losses in spring. Short term streamflow responses to winter inputs were larger and more efficient than spring and summer responses and their frequencies and magnitudes increased in 1968–2011 compared to 1929–1967. In total, 75% of the largest winter events were associated with atmospheric rivers, which can produce large cool-season streamflow peaks. We conclude that temperature-induced snow loss in this LCRB sub-basin was moderated by enhanced winter hydrological inputs and streamflow production.

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(ALL RIGHTS GRANTED TNC) View of Escudilla Mountain. Fall colors heighten the natural beauty of forest and meadow in the White Mountains, one of Arizona’s last wide-open spaces and where TNC works to protect the headwaters of three major Arizona rivers: the Salt, Gila, and Little Colorado and their greenbelts – riparian habitats critical for wildlife and water quality – as well as restore healthy forests within the largest ponderosa pine community in the world, save rare and unique wildlife and plant species, and control non-native, invasive species, such as crayfish, Arizona. © Betsy D. Warner/TNC
Aerial view of the Parks West restoration site overseen by TNC. Taken March 16, 2020.
Conservancy staffers, Dale Turner and Amanda Rebore, helping to map the Sabn Pedro River in Arizona. They use a GPS unit to denote the end of the water flow on the LowerSan Pedro River. They hiked through the Conservancy’s San Pedro Preserve.

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