Central Sierra Snow Laboratory Research Articles

Toward snowpack runoff decision support

SummaryRain-on-snow (ROS) events are commonly linked to large historic floods in the United States. Projected increases in the frequency and magnitude of ROS multiply existing uncertainties and risks in operational decision making. Here, we introduce a framework for quality-controlling hourly snow water content, snow depth, precipitation, and temperature data to guide the development of an empirically based snowpack runoff decision support framework at the Central Sierra Snow Laboratory for water years 2006–2019. This framework considers the potential for terrestrial water input from the snowpack through decision tree classification of rain-on-snow and warm day melt events to aid in pattern recognition of prominent weather and antecedent snowpack conditions capable of producing snowpack runoff. Our work demonstrates how (1) present weather and (2) antecedent snowpack risk can be “learned” from hourly data to support eventual development of basin-specific snowpack runoff decision support systems aimed at providing real-time guidance for water resource management.

Modeling the snow surface temperature with a one-layer energy balance snowmelt model

Abstract. Snow surface temperature is a key control on and result of dynamically coupled energy exchanges at the snow surface. The snow surface temperature is the result of the balance between external forcing (incoming radiation) and energy exchanges above the surface that depend on surface temperature (outgoing longwave radiation and turbulent fluxes) and the transport of energy into the snow by conduction and meltwater influx. Because of the strong insulating properties of snow, thermal gradients in snow packs are large and nonlinear, a fact that has led many to advocate multiple layer snowmelt models over single layer models. In an effort to keep snowmelt modeling simple and parsimonious, the Utah Energy Balance (UEB) snowmelt model used only one layer but allowed the snow surface temperature to be different from the snow average temperature by using an equilibrium gradient parameterization based on the surface energy balance. Although this procedure was considered an improvement over the ordinary single layer snowmelt models, it still resulted in discrepancies between modeled and measured snowpack energy contents. In this paper we evaluate the equilibrium gradient approach, the force-restore approach, and a modified force-restore approach when they are integrated as part of a complete energy and mass balance snowmelt model. The force-restore and modified force-restore approaches have not been incorporated into the UEB in early versions, even though Luce and Tartoton have done work in calculating the energy components using these approaches. In addition, we evaluate a scheme for representing the penetration of a refreezing front in cold periods following melt. We introduce a method to adjust effective conductivity to account for the presence of ground near to a shallow snow surface. These parameterizations were tested against data from the Central Sierra Snow Laboratory, CA, Utah State University experimental farm, UT, and subnivean snow laboratory at Niwot Ridge, CO. These tests compare modeled and measured snow surface temperature, snow energy content, snow water equivalent, and snowmelt outflow. We found that with these refinements the model is able to better represent the snowpack energy balance and internal energy content while still retaining a parsimonious one layer format.

스노우팩-융설 계산을 위한 에너지수지 알고리즘

Understanding snowmelt movement to the watershed is crucial for both climate change and hydrological studies because the snowmelt is a significant component of groundwater and surface runoff in temperature area. In this work, a new energy balance budget algorithm has been developed for melting snow from a snowpack at the Central Sierra Snow Laboratory (CSSL) in California, US. Using two sets of experiments, artificial rain-on-snow experiments and observations of diel variations, carried out in the winter of 2002 and 2003, we investigate how to calculate the amount of snowmelt from the snowpack using radiation energy and air temperature. To address the effect of air temperature, we calculate the integrated daily solar radiation energy input, and the integrated discharge of snowmelt under the snowpack and the energy required to generate such an amount of meltwater. The difference between the two is the excess (or deficit) energy input and we compare this energy to the average daily temperature. The resulting empirical relationship is used to calculate the instantaneous snowmelt rate in the model used by Lee et al. (2008a; 2010), in addition to the net-short radiation. If for a given 10 minute interval, the energy obtained by the melt calculation is negative, then no melt is generated. The input energy from the sun is considered to be used to increase the temperature of the snowpack. Positive energy is used for melting snow for the 10-minute interval. Using this energy budget algorithm, we optimize the intrinsic permeability of the snowpack for the two sets of experiments using one-dimensional water percolation model, which are <TEX>$52.5{\times}10^{-10}m^2$</TEX> and <TEX>$75{\times}10^{-10}m^2$</TEX> for the artificial rain-on-snow experiments and observations of diel variation, respectively.

Isotopic evolution of snowmelt: A new model incorporating mobile and immobile water

Isotopic variations of snowmelt provide important information for understanding snowmelt processes and the timing and contribution of snowmelt to catchments in spring. We report a new model for simulating the isotopic evolution of snowmelt. The model includes a hydraulic exchange between mobile and immobile water, and an isotopic exchange between liquid water (mobile and immobile water) and ice within a snowpack. Since this model is based on the mobile‐immobile water conceptualization, which is widely used for describing chemical tracer transport in snow, it allows simultaneous simulations of chemical as well as isotopic variations in snowpack discharge. We also report temporal variations of isotopic composition of a snowpack and snowmelt during artificial rain‐on‐snow experiments and diel snowmelt cycles observed in spring 2003 at the Central Sierra Snow Laboratory, California. These observations are used to test the newly developed model and to understand physical processes in a seasonal snowpack. Our model simulates the isotopic variations reasonably well, and suggests that exchanges of ice with both mobile and immobile water are important for determining the isotopic composition of the discharge.

Isotopic evolution of a seasonal snowcover and its melt by isotopic exchange between liquid water and ice

Understanding an isotopic evolution of a snowpack is important for both climate and hydrological studies, because the snowmelt is a significant component of groundwater and surface runoff in temperate areas. In this work, we studied oxygen and hydrogen isotopic evolution from new snow to snow profile and to meltwater through two winter seasons (1998 and 2001) at the Central Sierra Snow Laboratory, California, USA. The slopes of the δD vs. δ 18O regression for the new snow are similar to that of the global meteoric water line (GMWL) of 8. However, this slope decreases in the snow profile and decreases further in the meltwater. We attribute this systematic slope changes to the isotopic exchange between ice and liquid water that is generated at the snow surface by melting and flows through the snowpack by percolation. A physically-based one-dimensional model, including melting of snow at the surface and isotopic exchange between percolating water and ice, was used to simulate isotopic variation of snowmelt in 2001. A successful simulation was obtained for the δD– δ 18O slope of snowmelt (6.5), which is significantly lower than the slope of the meteoric water line (8.2) defined by the new snow. This result indicates that the liquid water evaporation should not be considered as the only process that yields slopes of the δD vs. δ 18O relationship in surface water and groundwater. The d-excess of the snowmelt is changed from the original snow because of the δD– δ 18O relationship controlled by ice–liquid exchange. With a δD– δ 18O slope less than 8, the d-excess would be anti-correlated with δD or δ 18O. The model is also used to examine how isotopic heterogeneity of a snowpack affects the isotopic redistribution in the pore water, ice and meltwater of the snowpack. The results show that isotopic heterogeneity of the snowpack may significantly affect the temporal changes in the δD– δ 18O slopes, and a measured slope at a given time is a combined result of meteorological conditions, which affect both isotopic composition of the original snow and the process of snow metamorphism, and the melting history of the snowpack.

A study of solute redistribution and transport in seasonal snowpack using natural and artificial tracers

Summary Solute releases from a seasonal snowpack are important features of spring runoff in temperate climate zones because meltwater accounts for a significant proportion of contaminant loading to catchments. Here we report a study that traces the movement of natural and artificial solutes in snow through the processes of snow deposition, snowpack metamorphism, and snowmelt at the Central Sierra Snow Laboratory (CSSL), Soda Springs, California, USA. Rare earth elements (REEs) were added to the snowpack to mark individual snow layers. New snow, snowpack profiles and snowmelt were sampled and analyzed for REE and anion ( SO 4 2 - , Cl− and NO 3 - ) concentrations. Correlations between NO 3 - and SO 4 2 - concentrations increased from new snow to snowpack profiles and to snow melt, suggesting significant redistributions of natural solutes in the snowpack. The maximum concentrations of NO 3 - and SO 4 2 - were both five times greater in the snow melt than in the new snow. Solute release by the snowpack was strongly controlled by weather conditions; high concentrations of natural tracers were observed at the onset of intensive melting episodes separated by relatively cold days of little melting. This weather pattern resulted in three ionic pulses rather than one. Natural solutes also showed a diurnal variation that was negatively correlated with the diurnal melting cycle. This pattern can be simulated by the standard water percolation equation linked with a mobile–immobile solute transport model (MIM). The diurnal variations of REE tracers showed positive association with the discharge, and cannot be satisfactorily simulated by the same model, suggesting that additional physical processes, such as dual or multiple flow regimes, may be needed to accurately describe solute transport in snow.

Isotope variations in a Sierra Nevada snowpack and their relation to meltwater

Isotopic variations in melting snow are poorly understood. We made weekly measurements at the Central Sierra Snow Laboratory, California, of snow temperature, density, water equivalent and liquid water volume to examine how physical changes within the snowpack govern meltwater δ 18O. Snowpack samples were extracted at 0.1 m intervals from ground level to the top of the snowpack profile between December 1991 and April 1992. Approximately 800 mm of precipitation fell during the study period with δ 18O values between −21.35 and −4.25‰. Corresponding snowpack δ 18O ranged from −22.25 to −6.25‰. The coefficient of variation of δ 18O in snowpack levels decreased from −0.37 to −0.07 from winter to spring, indicating isotopic snowpack homogenization. Meltwater δ 18O ranged from −15.30 to −8.05‰, with variations of up to 2.95‰ observed within a single snowmelt episode, highlighting the need for frequent sampling. Early snowmelt originated in the lower snowpack with higher δ 18O through ground heat flux and rainfall. After the snowpack became isothermal, infiltrating snowmelt displaced the higher δ 18O liquid in the lower snowpack through a piston flow process. Fractionation analysis using a two-component mixing model on the isothermal snowpack indicated that δ 18O in the initial and final half of major snowmelt was 1.30‰ lower and 1.45‰ higher, respectively, than the value from simple mixing. Mean snowpack δ 18O on individual profiling days showed a steady increase from −15.15 to −12.05‰ due to removal of lower δ 18O snowmelt and addition of higher δ 18O rainfall. Results suggest that direct sampling of snowmelt and snow cores should be undertaken to quantify tracer input compositions adequately. The snowmelt sequence also suggests that regimes of early lower δ 18O and later higher δ 18O melt may be modeled and used in catchment tracing studies.

Spatial Variability of Snow-Pack Outflow at a Site in Sierra Nevada, U.S.A.

Water flow through natural snow-packs is generally accepted to be extremely variable even over short distances. Differences in snow properties, and discontinuities in the horizontal and vertical structures of snow-packs, are responsible for variations in the effective area of the snow surface associated with outflow from a part of the base of the snow-pack. At the Central Sierra Snow Laboratory snow-pack outflow has been monitored using four snow-melt lysimeters of 6 m2 area each; two of these collectors were subdivided into three sections of equal area.Substantial variations in daily and monthly outflow volumes were noted between the individual collectors and also to a greater degree between the 2 m2 sub-units of the divided containers. The relative collecting efficiency of the snow-melt lysimeters also changed over time. In the deep warm snow-packs of the Sierra Nevada forest zone, snow-pack water routing appears to be highly variable, and this variability is on a much larger scale than was previously recognized. The large differences in snow-pack outflow measured in this study suggest that structural discontinuities and microtopography of snow strata can redirect percolating water over an area of several square meters.

Spatial Variability of Snow-Pack Outflow at a Site in Sierra Nevada, U.S.A.

Water flow through natural snow-packs is generally accepted to be extremely variable even over short distances. Differences in snow properties, and discontinuities in the horizontal and vertical structures of snow-packs, are responsible for variations in the effective area of the snow surface associated with outflow from a part of the base of the snow-pack. At the Central Sierra Snow Laboratory snow-pack outflow has been monitored using four snow-melt lysimeters of 6 m2 area each; two of these collectors were subdivided into three sections of equal area. Substantial variations in daily and monthly outflow volumes were noted between the individual collectors and also to a greater degree between the 2 m2 sub-units of the divided containers. The relative collecting efficiency of the snow-melt lysimeters also changed over time. In the deep warm snow-packs of the Sierra Nevada forest zone, snow-pack water routing appears to be highly variable, and this variability is on a much larger scale than was previously recognized. The large differences in snow-pack outflow measured in this study suggest that structural discontinuities and microtopography of snow strata can redirect percolating water over an area of several square meters.

Radiation Balances of Melting Snow Covers at an Open Site in the Central Sierra Nevada, California

The radiation balances of melting snowpacks for three seasons at an open site at the Central Sierra Snow Laboratory near Soda Springs, California were examined. The snow covers were examples of below‐normal, near‐normal and much‐above‐normal water equivalents. Two of the snow covers melted under generally clear skies in late spring while the other melted under cloudier conditions and at a time when less extraterrestrial radiation was available. Moreover, the snow covers were of very different densities, thereby allowing examination of a possible relationship between that characteristic and albedo. No such relationship was observed. Despite the dissimilarities in the conditions under which melt occurred, the disposition of solar radiation was similar for the three melt seasons. Albedos and their rates of decline through the melt season were similar for the three seasons. Absorbed solar radiation and a cloudiness index were useful predictors for daily net radiation, accounting for 71% of the total variance.

DISCUSSION

JAWRA Journal of the American Water Resources AssociationVolume 20, Issue 3 p. 455-456 DISCUSSION “The Potential for Increasing Streamflow from Sierra Nevada Watersheds”2 Kenneth M. Turner, Kenneth M. Turner Discussion No. 83213D of the Water Resources Bulletin 20(3):453-454.Search for more papers by this authorRichard C. Kattelmann, Richard C. Kattelmann Hydrologist Pacific Southwest Forest and Range Experiment Station, USDA Forest Service, Central Sierra Snow Laboratory, P.O. Box 66, Soda Springs, California 95728.Search for more papers by this authorNeil H. Berg, Neil H. Berg Hydrologist, Pacific Southwest Forest and Range Experiment Station, USDA Forest Service, Snow Zone Hydrology, P.O. Box 245, Berkeley, California 94701Search for more papers by this authorJohn Rector, John Rector Hydrologist, Pacific Southwest Region, USDA Forest Service, Watershed Management, 630 Sansome St., San Francisco, California 94111.Search for more papers by this author Kenneth M. Turner, Kenneth M. Turner Discussion No. 83213D of the Water Resources Bulletin 20(3):453-454.Search for more papers by this authorRichard C. Kattelmann, Richard C. Kattelmann Hydrologist Pacific Southwest Forest and Range Experiment Station, USDA Forest Service, Central Sierra Snow Laboratory, P.O. Box 66, Soda Springs, California 95728.Search for more papers by this authorNeil H. Berg, Neil H. Berg Hydrologist, Pacific Southwest Forest and Range Experiment Station, USDA Forest Service, Snow Zone Hydrology, P.O. Box 245, Berkeley, California 94701Search for more papers by this authorJohn Rector, John Rector Hydrologist, Pacific Southwest Region, USDA Forest Service, Watershed Management, 630 Sansome St., San Francisco, California 94111.Search for more papers by this author First published: June 1984 https://doi.org/10.1111/j.1752-1688.1984.tb04731.x 2 Paper No. 83080 of the Water Resources Bulletin 19(3):395-402. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume20, Issue3June 1984Pages 455-456 RelatedInformation

Development and testing of snow pack energy balance equations

By making several minor assumptions and using an empirical technique in one situation, the energy balance of a snow pack can be computed on a continuous basis. Net radiation or its components, air temperature, dew‐point temperature, atmospheric pressure, amount of precipitation and its temperature, surface snow density, and a wind function that relates vapor pressure gradient to moisture transfer as a function of wind speed, must be either measured or estimated. Comparison of computed versus observed snow pack runoff and snow surface temperature for the Lower Meadow lysimeter studies of 1954 at the Central Sierra Snow Laboratory reveals good agreement. A model was constructed by combining the energy balance equations with relationships describing the other components of the snow accumulation and ablation processes. The Stanford Watershed Model is used to determine the time delay from when water leaves the snow pack to the streamflow gaging station. Tests of the model on 5 years of data from the Central Sierra Snow Laboratory resulted in a reasonable simulation of the observed mean daily flow hydrograph and seasonal areal snow cover plot. It is concluded that the model is at least a good approximation to the actual physical processes and should be a valuable tool in further snow hydrology investigations.

Summer evapotranspiration trends as related to time after logging of forests in Sierra Nevada

The quantity of summer soil moisture lost from logged forest openings was related to the length of time since the creation of the opening, in the subalpine forest zone of the Sierra Nevada west side, near the Central Sierra Snow Laboratory, California, at an elevation of 6000 to 7000 feet. Soil moisture depletion was measured in forest openings which were created in 1959, 1955, 1950, and 1948, and in the forest surrounding these openings. Soil moisture was found to be uniformly near field capacity in all plots in early June. Later soil moisture was lost most rapidly from the forested parts of the plots and at progressively slower rates toward the center of the openings. The rate of moisture loss was greatest in early summer and then decreased as the availability of moisture decreased. Maximum soil moisture depletion occurred in early September, nearly all the available moisture being depleted from the forest. The quantity of residual soil moisture increased toward the center of the openings. At the period of maximum soil moisture depletion, openings 1 year old were found to have 6.9 inches more soil moisture per 4 feet of soil than the surrounding forest had, which is an expression of the quantity of moisture saved as a result of the logging operation. In openings 5 years old, the saving has decreased to 2.9 inches, after 10 years to 1.2 inches, and after 12 years to 0.7 inch. A projection of the regression indicates that the moisture saving at maximum depletion will become negligible 16 years after cutting.

Snow‐melt degree‐day ratios determined from snow‐lab data

Observations made at the Central Sierra Snow Laboratory in California and the Upper Columbia Snow Laboratory in western Montana have been used to determine the ratio of the amount of snow melt to the accumulated number of degree days or degree hours above selected base temperatures during the late spring melting season. The use of degree days was found to give smaller errors of estimation than degree hours, and a base temperature of 32°F gave smaller errors of estimation than other bases tried. The ratio was found to be smaller for greater forest cover and to increase during the melting season. No relation was found between the ratio and average wind, humidity, or cloudiness. These, of course, have important physical effects on the heat supply to a snow cover, but variations in their effect could be obscured by the fact that they were averaged over weekly or longer periods, and some of their effect may be included in the time‐of‐year parameter.

Discussion of “Forest‐cover effects on snowpack accumulation and melt, Central Sierra Snow Laboratory”

Anderson's ideal snow‐conservation forest and “Operation Snow Pack” (Western Water News, Aug. 1956) revive memories of Trans., AGU 1940, pp. 920–25, and Sci. Amer. Sup. Sep. 7, 1912 (Vol. 74, no. 1914).In 1912 while the Wagon Wheel Gap experiment was under way, I proposed the ‘honey‐comb’ forest, timber screens on the lips of canyons and timber‐line screens to accumulate and conserve the snow. In 1940 at Seattle, Charles A. Connaughton proposed a similar plan for the lodge‐pole‐pine forests of the Rocky Mountain Forest.

Forest‐cover effects on snowpack accumulation and melt, Central Sierra Snow Laboratory

Snowpack accumulation and melt at measurement points within snow courses were related to two forest‐cover variables. Water equivalent of the snowpack on April 1 of each year and melt rate after April 1 per unit of degree‐days above 35° F were studied. Cover variables were the amount of shade from trees to the south of a snow measurement point and the amount of shielding from trees to the north of the point. The amount of shade was expressed as the duration of shading between April 1 and June 15, multiplied by the amount of direct solar energy which would have struck the snow surface in the absence of shading. Shielding was expressed by the ratio of average tree height to distance of the trees from the measurement point. Datairom five points in each of five snow courses for three years of record were analyzed by the method of covariance. The analyses showed a high degree of association between the snowpack and forest‐cover variables. The results are interpreted in terms of the timber‐cutting pattern that would result in maximum accumulation of snow, minimum melt rate, and maximum prolonged release of snow water in the spring.

Penetration of radiation into the snow pack

A very sensitive pyrheliometer was designed and constructed by the author for measurement of the quantity of radiation transmitted through a snow pack. During March 1947, measurements of radiation transmission through the snow were made with this pyrheliometer at the Central Sierra Snow Laboratory. It was found that the depth to which radiation was transmitted increased as snow density increased. Absorption coefficients were obtained for snow between 20 and 40 per cent density. The presence of ice and slush in the snow surface resulted in a decreased albedo and increase in the amount of radiation absorbed. However, there was approximately 50 per cent reduction in tho amount of radiation transmitted through the ice and slush layer to lower horizons in the snow.