Subannual Streamflow Responses to Rainfall and Snowmelt Inputs in Snow‐Dominated Watersheds of the Western United States

Streamflow generation in mountain watersheds is strongly influenced by snow accumulation and melt, and multiple studies have found that snow loss leads to earlier snowmelt timing and declines in annual streamflow. However, hydrologic responses to snow loss are heterogeneous, and not all areas experi...

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Published in:Water resources research Vol. 56; no. 4
Main Authors: Hammond, John C., Kampf, Stephanie K.
Format: Journal Article
Language:English
Published: Washington John Wiley & Sons, Inc 01.04.2020
Subjects:
Annual precipitation
Annual variations
Base flow
Conservation
Digital filters
Geological surveys
hydrologic response
Hydrology
mountain hydrology
Mountains
Natural resources
natural resources conservation
Rain
Rainfall
Ratios
Resource conservation
Runoff
Snow
Snow accumulation
Snow-water equivalent
Snowmelt
Snowpack
spring
Stream discharge
Stream flow
streamflow
Surveying
Telemetry
United States Geological Survey
Watersheds
Winter
Western states
United States > US
ISSN:0043-1397, 1944-7973
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Summary:Streamflow generation in mountain watersheds is strongly influenced by snow accumulation and melt, and multiple studies have found that snow loss leads to earlier snowmelt timing and declines in annual streamflow. However, hydrologic responses to snow loss are heterogeneous, and not all areas experience streamflow declines. This research examines whether streamflow generation is different for rainfall versus snowmelt inputs. We compiled a sample of 57 small U.S. Geological Survey watersheds in the western United States containing a Natural Resource Conservation Service Snow Telemetry site and having ratios of mean annual peak snow water equivalent to precipitation ratios >0.25. Daily streamflow was separated into quickflow and baseflow using a digital filter, and quickflow was then divided into quickflow response intervals using thresholds in quickflow slope. Each quickflow response interval was categorized by its fraction of input from snowmelt. Most sites exhibited two streamflow generation peaks each year, with one peak in the winter when runoff efficiency is greatest, and the second in the spring during peak snowmelt input. On average, study watersheds were dominated by snowmelt inputs (70%), and snowmelt and mixed inputs usually generated greater streamflow than rainfall because of higher inputs and longer durations. However, rainfall produced high streamflow generation in winter, when watersheds have their highest runoff efficiency (81%) across all input types. We demonstrate that while snowmelt is important for streamflow generation due to high input over long periods, increases in rain and mixed input during wet winter periods can countervail tendencies for reduced streamflow with declining snowpacks. Key Points Quickflow response intervals (QRIs) are subannual hydrograph responses suitable for analyzing both snowmelt and rainfall‐dominated streamflow Snowmelt contributions to streamflow in western watersheds are lower than previous estimates, with most QRIs originating from mixed rain and snow input Snowmelt and mixed rain and snow QRIs produce more streamflow than rainfall‐dominated QRIs in most watersheds, except those with high winter rain and snowmelt input
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ISSN:0043-1397
1944-7973
DOI:10.1029/2019WR026132