Estimating the spatial and temporal distribution of snow in mountainous terrain

In-situ measurements and numerical models were used to quantify and improve understanding of the processes governing snowpack dynamics in mountainous terrain. Three studies were conducted in Sequoia National Park in the southern Sierra Nevada, California. The first two studies evaluated and simulate...

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Bibliographic Details
Main Author: Musselman, Keith Newton
Other Authors: Margulis, Steven A, Molotch, Noah P
Format: Other/Unknown Material
Language:English
Published: eScholarship, University of California 2012
Subjects:
Online Access:https://escholarship.org/uc/item/4p19x7bf
id ftcdlib:oai:escholarship.org/ark:/13030/qt4p19x7bf
record_format openpolar
institution Open Polar
collection University of California: eScholarship
op_collection_id ftcdlib
language English
topic Hydrologic sciences
Canopy
Distribution
Forest
Sierra Nevada
Snow
Variability
spellingShingle Hydrologic sciences
Canopy
Distribution
Forest
Sierra Nevada
Snow
Variability
Musselman, Keith Newton
Estimating the spatial and temporal distribution of snow in mountainous terrain
topic_facet Hydrologic sciences
Canopy
Distribution
Forest
Sierra Nevada
Snow
Variability
description In-situ measurements and numerical models were used to quantify and improve understanding of the processes governing snowpack dynamics in mountainous terrain. Three studies were conducted in Sequoia National Park in the southern Sierra Nevada, California. The first two studies evaluated and simulated the variability of observed melt rates at the point-scale in a mixed conifer forest. The third study evaluated the accuracy of a distributed snow model run over 1800 km2; a 3600 m elevation gradient that includes ecosystems ranging from semi-arid grasslands to massive sequoia stands to alpine tundra. In the first study, a network of 24 automated snow depth sensors and repeated monthly snow density surveys in a conifer forest were used to measure snow ablation rates for three years. A model was developed to estimate the direct beam solar radiation beneath the forest canopy from upward-looking hemispherical photos and above-canopy measurements. Sub-canopy solar beam irradiance and the bulk canopy metric sky view factor explained the most (58% and 87%, respectively) of the observed ablation rates in years with the least and most cloud cover, respectively; no single metric could explain > 41% of the melt rate variability for all years. In the second study, the time-varying photo-derived direct beam canopy transmissivity and the sky view factor canopy parameter were incorporated into a one-dimensional physically based snowmelt model. Compared to a bulk parameterization of canopy radiative transfer, when the model was modified to accept the time-varying canopy transmissivity, errors in the simulated snow disappearance date were reduced by one week and errors in the timing of soil water fluxes were reduced by 11 days, on average. In the third study, a distributed land surface model was used to simulate snow depth and SWE dynamics for three years. The model was evaluated against data from regional automated SWE measurement stations, repeated catchment-scale depth and density surveys, and airborne LiDAR snow depth data. In general, the model accurately simulated the seasonal maximum snow depth and SWE at lower and middle elevation forested areas. The model tended to overestimate SWE at upper elevations where no precipitation measurements were available. The SWE errors could largely be explained (R2 > 0.80, p<0.01) by distance of the SWE measurement from the nearest precipitation gauge. The results suggest that precipitation uncertainty is a critical limitation on snow model accuracy. Finally, an analysis of seasonal and inter-annual snowmelt patterns highlighted distinct melt differences between lower, middle, and upper elevations. Snowmelt was generally most frequent (70% - 95% of the snow-covered season) at the lower elevations where snow cover was ephemeral and seasonal mean melt rates computed on days when melt was simulated were generally low (< 3 mm day-1). At upper elevations, melt occurred during less than 65% of the snow-covered period, it occurred later in the season, and mean melt rates were the highest of the region (> 6 mm day-1). Middle elevations remained continuously snow covered throughout the winter and early spring, were prone to frequent but intermittent melt, and provided the most sustained period of seasonal mean snowmelt (~ 5 mm day-1). The melt dynamics (e.g. timing and melt rate) unique to these middle elevations may be critical to the local forest ecosystem. Furthermore, the three years evaluated in this study indicate a marked sensitivity of this elevation range to seasonal meteorology, suggesting that it could be highly sensitive to future changes in climate.
author2 Margulis, Steven A
Molotch, Noah P
format Other/Unknown Material
author Musselman, Keith Newton
author_facet Musselman, Keith Newton
author_sort Musselman, Keith Newton
title Estimating the spatial and temporal distribution of snow in mountainous terrain
title_short Estimating the spatial and temporal distribution of snow in mountainous terrain
title_full Estimating the spatial and temporal distribution of snow in mountainous terrain
title_fullStr Estimating the spatial and temporal distribution of snow in mountainous terrain
title_full_unstemmed Estimating the spatial and temporal distribution of snow in mountainous terrain
title_sort estimating the spatial and temporal distribution of snow in mountainous terrain
publisher eScholarship, University of California
publishDate 2012
url https://escholarship.org/uc/item/4p19x7bf
genre Tundra
genre_facet Tundra
op_relation qt4p19x7bf
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op_rights public
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spelling ftcdlib:oai:escholarship.org/ark:/13030/qt4p19x7bf 2023-05-15T18:40:49+02:00 Estimating the spatial and temporal distribution of snow in mountainous terrain Musselman, Keith Newton Margulis, Steven A Molotch, Noah P 2012-01-01 application/pdf https://escholarship.org/uc/item/4p19x7bf en eng eScholarship, University of California qt4p19x7bf https://escholarship.org/uc/item/4p19x7bf public Hydrologic sciences Canopy Distribution Forest Sierra Nevada Snow Variability etd 2012 ftcdlib 2019-12-06T23:53:14Z In-situ measurements and numerical models were used to quantify and improve understanding of the processes governing snowpack dynamics in mountainous terrain. Three studies were conducted in Sequoia National Park in the southern Sierra Nevada, California. The first two studies evaluated and simulated the variability of observed melt rates at the point-scale in a mixed conifer forest. The third study evaluated the accuracy of a distributed snow model run over 1800 km2; a 3600 m elevation gradient that includes ecosystems ranging from semi-arid grasslands to massive sequoia stands to alpine tundra. In the first study, a network of 24 automated snow depth sensors and repeated monthly snow density surveys in a conifer forest were used to measure snow ablation rates for three years. A model was developed to estimate the direct beam solar radiation beneath the forest canopy from upward-looking hemispherical photos and above-canopy measurements. Sub-canopy solar beam irradiance and the bulk canopy metric sky view factor explained the most (58% and 87%, respectively) of the observed ablation rates in years with the least and most cloud cover, respectively; no single metric could explain > 41% of the melt rate variability for all years. In the second study, the time-varying photo-derived direct beam canopy transmissivity and the sky view factor canopy parameter were incorporated into a one-dimensional physically based snowmelt model. Compared to a bulk parameterization of canopy radiative transfer, when the model was modified to accept the time-varying canopy transmissivity, errors in the simulated snow disappearance date were reduced by one week and errors in the timing of soil water fluxes were reduced by 11 days, on average. In the third study, a distributed land surface model was used to simulate snow depth and SWE dynamics for three years. The model was evaluated against data from regional automated SWE measurement stations, repeated catchment-scale depth and density surveys, and airborne LiDAR snow depth data. In general, the model accurately simulated the seasonal maximum snow depth and SWE at lower and middle elevation forested areas. The model tended to overestimate SWE at upper elevations where no precipitation measurements were available. The SWE errors could largely be explained (R2 > 0.80, p<0.01) by distance of the SWE measurement from the nearest precipitation gauge. The results suggest that precipitation uncertainty is a critical limitation on snow model accuracy. Finally, an analysis of seasonal and inter-annual snowmelt patterns highlighted distinct melt differences between lower, middle, and upper elevations. Snowmelt was generally most frequent (70% - 95% of the snow-covered season) at the lower elevations where snow cover was ephemeral and seasonal mean melt rates computed on days when melt was simulated were generally low (< 3 mm day-1). At upper elevations, melt occurred during less than 65% of the snow-covered period, it occurred later in the season, and mean melt rates were the highest of the region (> 6 mm day-1). Middle elevations remained continuously snow covered throughout the winter and early spring, were prone to frequent but intermittent melt, and provided the most sustained period of seasonal mean snowmelt (~ 5 mm day-1). The melt dynamics (e.g. timing and melt rate) unique to these middle elevations may be critical to the local forest ecosystem. Furthermore, the three years evaluated in this study indicate a marked sensitivity of this elevation range to seasonal meteorology, suggesting that it could be highly sensitive to future changes in climate. Other/Unknown Material Tundra University of California: eScholarship