Abstract
Abstract. Many forested watersheds with a substantial fraction of precipitation delivered as snow have the potential for landscape disturbance by wildfire. Little is known about the immediate effects of wildfire on snowmelt and near-surface hydrologic responses, including soil-water storage. Montane systems at the rain-snow transition have soil-water dynamics that are further complicated during the snowmelt period by strong aspect controls on snowmelt and soil thawing. Here we present data from field measurements of snow hydrology and subsurface hydrologic and temperature responses during the first winter and spring after the September 2010 Fourmile Canyon Fire in Colorado, USA. Our observations of soil-water content and soil temperature show sharp contrasts in hydrologic and thermal conditions between north- and south-facing slopes. South-facing burned soils were ∼1–2 °C warmer on average than north-facing burned soils and ∼1.5 °C warmer than south-facing unburned soils, which affected soil thawing during the snowmelt period. Soil-water dynamics also differed by aspect: in response to soil thawing, soil-water content increased approximately one month earlier on south-facing burned slopes than on north-facing burned slopes. While aspect and wildfire affect soil-water dynamics during snowmelt, soil-water storage at the end of the snowmelt period reached the value at field capacity for each plot, suggesting that post-snowmelt unsaturated storage was not substantially influenced by aspect in wildfire-affected areas. Our data and analysis indicate that the amount of snowmelt-driven groundwater recharge may be larger in wildfire-impacted areas, especially on south-facing slopes, because of earlier soil thaw and longer durations of soil-water contents above field capacity in those areas.
Highlights
1.1 Motivation and previous researchMountainous regions are important sources of surface and groundwater to downgradient population centers
Snow depths and air temperatures were measured at the northfacing midslope (NFM) plot with a Judd Communications ultrasonic depth sensor (Judd Communications, Salt Lake City, USA) using 3min temporal resolution and a 1-h running mean of the data to smooth out noise, as recommended by Brazenec (2005)
The decline in snow-water equivalent (SWE) coupled with increases in snow density at the north-facing plots (NFM and north-facing ridge (NFR)) led to snowpack disappearance on 10 March, reflecting microtopographic and shading influences on snow accumulation and melt between the ultrasonic sensor and SWE plots (Figs. 3 and 4a, b)
Summary
1.1 Motivation and previous researchMountainous regions are important sources of surface and groundwater to downgradient population centers. In the USA over 60 million people depend on water from mountain river basins (Bales et al, 2006). Much of the precipitation in mountain areas falls as snow such that snowmelt contributes the majority of regional water supplies In the previous 30 yr, wildfire incidence and the duration of fire-prone conditions has increased in the mountainous western USA, which can be partially attributed to earlier snowmelt (Westerling et al, 2006). The increasing pressure of wildfire and its potential impact on much-needed mountain water supplies Ice et al, 2004) creates an imperative that we increase our understanding of wildfire interactions with snowmelt-driven hydrologic response The increasing pressure of wildfire and its potential impact on much-needed mountain water supplies (e.g. Ice et al, 2004) creates an imperative that we increase our understanding of wildfire interactions with snowmelt-driven hydrologic response
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