Measurements of sensible and latent heat fluxes using eddy covariance (EC) instrumentation over s... more Measurements of sensible and latent heat fluxes using eddy covariance (EC) instrumentation over snow in complex terrain have become more common in the past decade. Analysis of EC measurements at two sites, wind-exposed and wind-protected, for three consecutive years is presented. The analysis focused on how site conditions influence inter-annual variability of EC-measured turbulent fluxes. The protected site yields essentially the same turbulent fluxes, regardless of meteorological inter-annual variability. The exposed site yields turbulent fluxes that are several times the magnitude of the fluxes measured at the protected site. Sublimation for the season is relatively constant for the years studied, and hence constitute a larger percentage of the snow pack during below average water years. Sensible heat dominates the turbulent flux early in the season while latent heat dominates turbulent fluxes later in the season.
Physically-based, spatially distributed hydrologic models typically require a large numbers of pa... more Physically-based, spatially distributed hydrologic models typically require a large numbers of parameters which must be measured or estimated for catchments of interest. Meteorological data used to drive models are critical to accurate output, but are frequently difficult to measure accurately and continuously at remote locations. To answer the question of how the error from each of the input parameters and variables affect model outputs, a sensitivity analysis of the Distributed Hydrology Soil-Vegetation Model (DHSVM) was completed. A rigorous five-year calibration of the model was completed and validated with internal catchment variables including soil water content, snow water equivalent, and sapflow at the Mica Creek Experimental Watershed (MCEW) in northern Idaho. Following the model validation, a series of systematic model runs were completed to explore the sensitivity of the catchment outflow to state parameters and climate variables. A ten percent increase in precipitation was found to increase water yield by 24.67% and peakflow by 19.67% in the five-year study period. An air temperature increase of two degrees C increased ET by 35.4% and reduced water yield by 15.9%. The 50th percentile of annual flow was advanced by 45 days for the 2 degree C air temperature increase, and by 16 days for a 1 degree C increase. The 5% peakflow was reduced by 24% and enhanced by 20% with the air temperature and precipitation increment, respectively. The model was surprisingly sensitive to relative humidity, where a 10% increase produced a 37.6% in water yield and increased the 5% peakflow by 20%. The soil properties greatly affect the water yield and annual streamflow timing in a by changing the soil water storage. For example, switching from silt loam to silty clay increases water yield by 24% and to loamy sand advances 50th percentile flow by 6 days. Although these results are site specific, the modeling results from air temperature and precipitation sensitivity tests indicate the importance of accurate hydrometeorological data collection. These results also suggest the degree of sensitivity to future climate scenarios that indicate warmer and potentially wetter conditions for this region.
A screening-level in vitro test was developed to evaluate the relative solubility of ingested lea... more A screening-level in vitro test was developed to evaluate the relative solubility of ingested lead (Pb) from different mine wastes in the gastrointestinal (GI) tract. The in vitro method, modeled after assay methods for available iron from food, used a laboratory digestion procedure designed to reproduce GI tract chemistry and function. The in vitro method was independently calibrated against a rabbit feeding study, demonstrating that only 1-6% of the total Pb in four mine-waste samples with disparate Pb mineralogy was bioaccessible. I n vitro method development tests indicated that H+ concentration and C1complexation control dissolution of Pb-bearing minerals in the stomach and that both GI tract enzymes and organic acids are necessary to maintain Pb in the soluble form on entering the small intestine, The experimental results indicate that ingestion of Pb-bearing mine wastes results in limited Pb solubility and that the in vitro test provides a screening-level estimate of the maximum available Pb from mine wastes.
Long-term water balance investigations are needed to better understand hydrologic systems, especi... more Long-term water balance investigations are needed to better understand hydrologic systems, especially semi-arid mountainous catchments. These systems exhibit considerable interannual variability in precipitation as well as spatial variation in snow accumulation, soils, and vegetation. This study extended a previous 10-year water balance based on measurements and model simulations to 24 years for the Upper Sheep Creek (USC) catchment, a 26 ha, snow-fed, semi-arid rangeland headwater drainage within the Reynolds Creek Experimental Watershed in southwestern Idaho, USA. Additional analyses afforded by the additional years of data demonstrated that the variability between streamflow and annual precipitation (r 2 = 0.54) could be explained by the timing of precipitation and antecedent moisture conditions. Winter-spring precipitation and soil moisture deficit at the beginning of the water year accounted for 83% of the variability in streamflow, which was almost as accurate as applying the more complex physically-based Simultaneous Heat and Water (SHAW) numerical model (r 2 = 0.85) over the three dominant land cover classes. A conceptual model was formulated based on field observations, numerical simulations and previous studies. Winter precipitation and spring snowmelt must first replenish the deficit within the soil water profile and ground water system before water is delivered to the stream. During this period, surface water and ground water are tightly coupled and their interaction is critical to streamflow generation. Shortly after snow ablation, however, water flux in the root zone becomes decoupled from the ground water system and subsequent precipitation does little to contribute to streamflow for the current year, but serves to offset ET and the soil moisture deficit at the beginning of the following year. This study demonstrates the merits of long-term catchment-scale research to improve our understanding of how climate and land cover interact to control hydrologic dynamics in complex mountainous terrain.
Energy balance models use physically based principles to simulate snow cover accumulation and mel... more Energy balance models use physically based principles to simulate snow cover accumulation and melt. Snobal, a snow cover energy balance model, uses a flux-profile approach to calculating the turbulent flux (sensible and latent heat flux) components of the energy balance. Historically, validation data for turbulent flux simulations have been difficult to obtain at snow dominated sites characterized by complex terrain and heterogeneous vegetation. Currently, eddy covariance (EC) is the most defensible method available to measure turbulent flux and hence to validate this component of an energy balance model. EC was used to measure sensible and latent heat flux at two sites over three winter seasons (2004, 2005, and 2006). Both sites are located in Reynolds Creek Experimental Watershed in southwestern Idaho, USA and are characterized as semi-arid rangeland. One site is on a wind-exposed ridge with small shrubs and the other is in a wind-protected area in a small aspen stand. EC data were post processed from 10 Hz measurements. The first objective of this work was to compare EC- measured sensible and latent heat flux and sublimation/condensation to Snobal-simulated values. Comparisons were made on several temporal scales, including inter-annual, seasonal and diurnal. The flux- profile method used in Snobal assumes equal roughness lengths for moisture and temperature, and roughness lengths are constant and not a function of stability. Furthermore, there has been extensive work on improving profile function constants that is not considered in the current version of Snobal. Therefore, the second objective of this work was to modify the turbulent flux algorithm in Snobal. Modifications were made to calculate roughness lengths as a function of stability and separately for moisture and temperature. Also, more recent formulations of the profile function constants were incorporated. The third objective was to compare EC-measured sensible and latent heat flux and sublimation/condensation to the modified Snobal simulated values. The final objective was to determine if the modified turbulent flux algorithm in Snobal results in hydrologically significant improvements to simulations.
Proceedings 2011 IEEE International Conference on Spatial Data Mining and Geographical Knowledge Services, 2011
Digital elevation model (DEM) is one of the most important information that can be derived from t... more Digital elevation model (DEM) is one of the most important information that can be derived from the airborne LiDAR data. However in areas covered by dense vegetation, the chance of laser passing through the canopy, hitting the ground and back to the receiver is limited, thus it is difficult to achieve accurate DEM in regions with dense vegetative covers (trees, shrubs and grasses). We considered the challenges in deriving accurate terrain elevation information from LiDAR data: identifying areas covered with dense vegetation, separating LiDAR point clouds into ground and non-ground returns, interpolating to create raster surface models. A case study in the semi-arid mountainous area of the Northwest US shows that dense shrub caused about 20 cm DEM error in vertical accuracy, in line with similar study results of LiDAR derived DEM from dense grass areas. Terrain, cover type and LiDAR acquisition parameters (scan or incidence angle, point density) can also affect accuracy.
Radiation fields are required to model snow and hydrologic processes and properties over forested... more Radiation fields are required to model snow and hydrologic processes and properties over forested mountain regions. We present a method that utilizes a representation of terrain and forest structure (height, crown and trunk shape, canopy density and spacing) to modulate above-canopy solar and thermal radiation fields for canopy shading and emissivity effects. The method preserves gap fraction, and accounts for terrain features of slope, aspect and local horizon-induced terrain shading. The method is initiated over a very high resolution, pre-determined distribution of canopy crowns and gaps. For development of the method, terrain structure information was derived from a LiDAR representation of both terrain and canopy over the Fraser Experimental Forest in Colorado. The method can also be applied to an artificial canopy structure, based on a statistical distribution of canopy crowns and gaps as simulated over a region. Though the method is computationally expensive, once the shading and emissivity functions have been computed for a full range of azmuthal conditions, they can be retained in look-up tables, and scaled to an arbitrary set of radiation conditions. The method is applied over the LiDAR domain at the Colorado site using by correcting above-canopy radiation fields for a series of selected dates representing high and low sun angles, and a variety of snow depth conditions.
The impacts of timber harvesting practices on the flow regime, water and isotope mass balance (2H... more The impacts of timber harvesting practices on the flow regime, water and isotope mass balance (2H, 2O) in a mountainous catchment were studied over the period from 2004 to 2007. The Mica Creek Experimental Watershed (MCEW) is located in northwestern Idaho, USA (97 km2, 975 - 1,750 m a.s.l.). It includes three sub watersheds of comparable physical conditions with clear-cut (100 % removal in 50 % of the area, CC), partial-cut (50 % removal in 50 % of the area, PC), and unimpacted (control forest, CF) sites. Precipitation, spring water, stream flow, soil water, and sap flow were collected for stable isotope analyses on a monthly basis during the growing season. Snow, which is the dominant water input in this region, was intensively studied during winter 2005/06. A base flow sampling campaign was conducted during low flow in September 2006. Weekly analyses of precipitation indicate isotopic variations ranging between -3.9 ‰ and -22.0 ‰ and -42 ‰ and -170 ‰ for δ2O and δ2H, respectively. Isotopic composition of snow samples obtained in 2006 from snow profiles at snow courses varied between -13.8 ‰ and -17.5 ‰ for δ2O and δ2H values varied between -102 ‰ and -129 ‰. The isotopic composition of snow reflects enrichment due to intercepted snow sublimation and evaporation in the dense forest sites. Stream flow samples are in the range of -15.7 ‰ and -113 ‰ for δ2O and δ2H, respectively. Mean soil water concentrations of the upper 20 cm for the CC, PC and CF sites show values of -15.4 ‰, -14.1 ‰, -13.3 ‰ and -123 ‰, -114 ‰, -109 ‰ for δ2O and δ2H, respectively. Sap flow appeared to reflect differential canopy interception losses, with greater enrichment under the densest canopies (-14.4 ‰, -14.2 ‰, -13.8 ‰ for δ2O of CC, PC, CF and -130 ‰, -124 ‰, -119 ‰ for δ2H of CC, PC, CF, respectively). Presumably, variations reflect fluctuating rates of precipitation, deposition, ablation and sublimation of the snow cover. Stream water, soil water and plant water follow these patterns indicating that water isotope concentrations vary throughout physiographically similar areas as a result of land cover differences. Water isotope fluxes were calculated and allowed improved estimates of evapotranspiration of the forest treatments.
The turbulent exchange of sensible and latent heat and mass between the snowcover and the atmosph... more The turbulent exchange of sensible and latent heat and mass between the snowcover and the atmosphere can represent a significant component of the snowcover energy and mass balance in mountainous environments. These fluxes are computed in land surface and energy balance snowmelt models, though few measurements exist for comparison or validation. Where measurements do exist, they employ eddy covariance (EC) instrumentation. Two outputs are generated with typical eddy covariance instrumentation: time series data, which is later corrected and fluxes calculated, and 30-minute flux summaries, which are calculated directly without correction. Due to data storage limitations, the flux summaries are often stored instead of raw time series data. More commonly, turbulent fluxes are modeled from slow response meteorologic data. This research considers data taken from within a forested site over snow in order to compare turbulent fluxes estimated from the two eddy covariance output types and modeled turbulent fluxes. Preliminary results indicate corrected time series fluxes are approximately 15%-20% smaller than 30-minute flux summaries, and approximately equivalent to the modeled fluxes at this site. The conditions under which the labor-intensive time series corrections are mandatory are described. Also, the conditions under which the 30-minute flux summaries and modeled fluxes are similar to time series estimated turbulent fluxes are described. The steps used to process, correct, and analyze (including co-spectra) the time series eddy covariance data are presented. The data used in this analysis are from a uniform conifer stand during the winter of 2003 as part of the Cold Lands Processes Field Experiment (CLPX). This research improves our understanding of how measurements of turbulent fluxes vary by estimation method and sets the stage for improved modeling of turbulent fluxes.
Long-term water balance investigations are needed to better understand hydrologic systems, especi... more Long-term water balance investigations are needed to better understand hydrologic systems, especially semi-arid mountainous catchments. These systems exhibit considerable inter-annual variability in precipitation as well as spatial variation in snow accumulation, soils, and vegetation. Long-term studies that capture a wide range of conditions can be used to gain insight into potential future hydrologic regimes. This study used the Simultaneous Heat and Water (SHAW) model to quantify the hydrological fluxes over 24 years at the Upper Sheep Creek catchment, a 26 ha, snow-fed, semi-arid headwater drainage within the Reynolds Creek Experimental Watershed in southwestern Idaho, USA. The quantity of data afforded by the 24-year study allowed a more complete conceptual model of the system to be developed, and detailed analyses of both inter- and intra-annual flow variations. In this system, winter precipitation and spring snowmelt must first replenish the deficit within the soil water profile and ground water system before water is delivered to the stream. During this period, surface water and ground water are tightly coupled, and their interaction is critical to streamflow generation. Shortly after snow ablation however, water flux in the root zone becomes decoupled from the ground water system and subsequent precipitation does little to contribute to streamflow for the current year. Data indicated that relatively wet years characterized by drier winter and wetter spring months exhibited lower runoff ratios compared to relatively dry years with early snowmelt which exhibited higher runoff ratios. The former case appears to be due to less spatially variable precipitation due to reduced snow distribution and late-season replenishment of the soil moisture reservoir during the growing season. These dynamics suggest that projected future climate conditions characterized by stable or increased precipitation and increased rain/snow ratios may exhibit lower annual water yields due to increased evaporative fractions. This interpretation is supported by simulations of projected flow regime changes at a nearby forested watershed using downscaled GCM data, which indicate increased winter and spring evapotranspiration and declining annual hydrologic yields.
In the Pacific Northwest (PNW), concern about the impacts of climate and land cover change on wat... more In the Pacific Northwest (PNW), concern about the impacts of climate and land cover change on water resources and flood-generating processes emphasize the need for a mechanistic understanding of the interactions between forest canopies and hydrological processes. A detailed measurement and modeling program in the 1999 and 2000 hydrologic years characterized hydrological processes in a 500-600 year old Douglas fir-western hemlock seasonal temperate rainforest. The measurement program included sub-canopy arrays of radiometers, tipping bucket rain gauges, and soil temperature and moisture probes, to supplement a vertical temperature and humidity profile within the forest canopy. The measurements were used to modify the Simultaneous Heat and Water (SHAW) Model for application in forested systems. Changes to the model include improved representation of interception dynamics, stomatal conductance, and within- canopy energy transfer processes. The model was calibrated for the 1999 hydrologic year, and validated for the 2000 season. The model effectively simulated canopy air and vapor density profiles, snowcover processes, throughfall, soil water content profiles, shallow soil temperatures, and transpiration fluxes for both years. The largest discrepancies between soil moisture and temperature were observed during periods of discontinuous snowcover. Soil warming at bare locations was delayed until most of the snowcover ablated due to the large heat sink associated with the residual snow patches. During the summer, simulated evapotranspiration decreased from a maximum monthly mean of 2.17 mm day-1 in July to 1.34 mm day-1 in September, as a result of decreasing soil moisture and declining net radiation. Our results indicate that a relatively simple parameterization of the SHAW model for the vegetation canopy can accurately simulate seasonal hydrological fluxes in this environment. The model could be used to assess the potential effects of climate or landcover changes on hydrological processes in PNW old-growth ecosystems. Application and validation of the model in other forest systems will establish similarities and differences in the interactions of vegetation and hydrology, and assess the sensitivity of other systems to natural and anthropogenic perturbations. >http://ucs.orst.edu/~linkt/wrccrf/index.html</a>
Sensible and latent heat and mass flux represent a significant component of the snowcover energy ... more Sensible and latent heat and mass flux represent a significant component of the snowcover energy and mass balance in mountain environments. Though these fluxes are computed in energy balance snow models, limited measurements exist for comparison or validation in complex, mountainous sites. Sensible and latent heat and mass flux can be determined directly from the turbulent fluctuations measured by fast-response sensors using eddy covariance (EC) theory. Two EC study sites, which are operated through the winter, were located in southwestern Idaho in a small headwater catchment of the Reynolds Creek Experimental Watershed, located approximately 80 km southwest of Boise, Idaho. One, a protected, below canopy site is located within a stand of aspen trees, and the other, an exposed site, is located nearby on a ridge over mixed sagebrush. Corrections and post-processing of eddy covariance data are discussed and EC-measured fluxes from the two sites are compared to better understand the manner in which terrain and vegetation influence turbulent fluxes over snow. Turbulent fluxes are also modeled at these two sites using the Snobal energy balance snow model, and differences between simulated and measured fluxes are evaluated. This research will improve our understanding of how heat and mass flux from the snowcover impacts water resources in areas dominated by, high winds, complex terrain and variable vegetation conditions, provide validation data for snow models, and ultimately improve water supply forecasts required for management decisions.
In mountainous, forested environments, snowcover dynamics exert a strong control on hydrologic an... more In mountainous, forested environments, snowcover dynamics exert a strong control on hydrologic and atmospheric processes. Snowcover ablation patterns in forests are controlled by a complex combination of depositional patterns coupled with radiative and turbulent heat flux patterns related to topographic and canopy cover variations. Quantification of small-scale variations of radiant energy in forested environments is necessary to understand how canopy structure affects snowcover energetics to improve spatially-explicit physically-based snowmelt models. Incoming solar and thermal radiation patterns were measured during the melt season around individual trees in isolated deciduous and coniferous forest patches. During clear to partly cloudy conditions, solar radiation around the leafless deciduous tree was reduced by 68%, whereas thermal radiation was enhanced by 26%. Under similar meteorological conditions, solar radiation was reduced by 87% and thermal radiation was enhanced by 43% beneath the crown of the coniferous tree. To assess potential impacts of radiative differences between open and sub-canopy net snowcover radiation, a simple analysis of sensitivity of net snowcover radiation to a range of snowcover albedo values was completed. For the meteorological conditions during this study, the analysis indicates that the deciduous canopy is likely to have a minor impact on net radiation differences. The area beneath the coniferous crown is expected to exhibit enhanced net radiation for relatively high (>0.6) open site albedo values. A small forest gap is expected to exhibit minimal difference relative to open sites for typical albedo values, whereas a large gap is expected to exhibit less net radiation than open areas. During cloudy to overcast conditions, net radiation at all canopy locations is expected to be lower than at open sites. These net radiation differences coupled with decreased turbulent fluxes due to lower wind velocities and reduced snow water equivalent values due to canopy interception losses help to explain small-scale patterns of snowmelt in non-uniform forested areas. This work also emphasizes the need to consider canopy heating in sparse forest and edge environments and to develop an improved understanding of sub-canopy snowcover albedo patterns and dynamics.
Sensible and latent heat and mass fluxes can represent a significant component of the snowcover e... more Sensible and latent heat and mass fluxes can represent a significant component of the snowcover energy and mass balance in mountain environments. Though these fluxes are computed in energy balance snow models, few measurements exist for comparison or validation. This research investigates the methodology required and problems associated with the direct measurement of sensible and latent heat flux over snow. The sensible and latent heat and mass fluxes can be determined directly from the turbulent fluctuations measured by fast-response sensors using eddy covariance (EC) theory. The general site considerations and specific weather conditions common to mountain catchments that affect EC data collection over snow is explored. Corrections and post-processing of eddy covariance data is discussed. Examples from established EC measurement sites under adverse and optimal conditions will be presented. The two primary EC study sites are located in southwestern Idaho in a small headwater catchment of the Reynolds Creek Experimental Watershed, located approximately 80 km southwest of Boise, Idaho. A protected, below canopy site is located within a stand of aspen trees, and an exposed site is located on a ridge over big mountain sagebrush. The study investigates the conditions under which EC instrument systems can be used in mountainous, snow-dominated environments, the processing required to prepare the data for analysis, and several examples of post-processed data collected over snow. This research will improve our understanding of how heat and mass flux from the snowcover may impact water resources under the variable and changing climate conditions so common in the Western US.
Forest canopies strongly affect the radiation balance of snowcovers by reducing solar radiation a... more Forest canopies strongly affect the radiation balance of snowcovers by reducing solar radiation at the snow surface, decreasing the snow surface albedo, and enhancing incoming thermal radiation at the snow surface relative to open areas. During radiation-driven snowmelt, thermal radiation is commonly the dominant component of melt energy in forests. The relative importance of solar and thermal radiation for snowmelt
A suite of detailed experimental measurements and modeling are used to evaluate how snow distribu... more A suite of detailed experimental measurements and modeling are used to evaluate how snow distribution and melt are influenced by vegetation and topographic structure across different experimental catchments in western North America (two in the western US, and one in western Canada). Critical interactions between vegetation, topography and snowcover in snow-dominated basins are investigated to evaluate how these differences impact
Measurements of sensible and latent heat fluxes using eddy covariance (EC) instrumentation over s... more Measurements of sensible and latent heat fluxes using eddy covariance (EC) instrumentation over snow in complex terrain have become more common in the past decade. Analysis of EC measurements at two sites, wind-exposed and wind-protected, for three consecutive years is presented. The analysis focused on how site conditions influence inter-annual variability of EC-measured turbulent fluxes. The protected site yields essentially the same turbulent fluxes, regardless of meteorological inter-annual variability. The exposed site yields turbulent fluxes that are several times the magnitude of the fluxes measured at the protected site. Sublimation for the season is relatively constant for the years studied, and hence constitute a larger percentage of the snow pack during below average water years. Sensible heat dominates the turbulent flux early in the season while latent heat dominates turbulent fluxes later in the season.
Physically-based, spatially distributed hydrologic models typically require a large numbers of pa... more Physically-based, spatially distributed hydrologic models typically require a large numbers of parameters which must be measured or estimated for catchments of interest. Meteorological data used to drive models are critical to accurate output, but are frequently difficult to measure accurately and continuously at remote locations. To answer the question of how the error from each of the input parameters and variables affect model outputs, a sensitivity analysis of the Distributed Hydrology Soil-Vegetation Model (DHSVM) was completed. A rigorous five-year calibration of the model was completed and validated with internal catchment variables including soil water content, snow water equivalent, and sapflow at the Mica Creek Experimental Watershed (MCEW) in northern Idaho. Following the model validation, a series of systematic model runs were completed to explore the sensitivity of the catchment outflow to state parameters and climate variables. A ten percent increase in precipitation was found to increase water yield by 24.67% and peakflow by 19.67% in the five-year study period. An air temperature increase of two degrees C increased ET by 35.4% and reduced water yield by 15.9%. The 50th percentile of annual flow was advanced by 45 days for the 2 degree C air temperature increase, and by 16 days for a 1 degree C increase. The 5% peakflow was reduced by 24% and enhanced by 20% with the air temperature and precipitation increment, respectively. The model was surprisingly sensitive to relative humidity, where a 10% increase produced a 37.6% in water yield and increased the 5% peakflow by 20%. The soil properties greatly affect the water yield and annual streamflow timing in a by changing the soil water storage. For example, switching from silt loam to silty clay increases water yield by 24% and to loamy sand advances 50th percentile flow by 6 days. Although these results are site specific, the modeling results from air temperature and precipitation sensitivity tests indicate the importance of accurate hydrometeorological data collection. These results also suggest the degree of sensitivity to future climate scenarios that indicate warmer and potentially wetter conditions for this region.
A screening-level in vitro test was developed to evaluate the relative solubility of ingested lea... more A screening-level in vitro test was developed to evaluate the relative solubility of ingested lead (Pb) from different mine wastes in the gastrointestinal (GI) tract. The in vitro method, modeled after assay methods for available iron from food, used a laboratory digestion procedure designed to reproduce GI tract chemistry and function. The in vitro method was independently calibrated against a rabbit feeding study, demonstrating that only 1-6% of the total Pb in four mine-waste samples with disparate Pb mineralogy was bioaccessible. I n vitro method development tests indicated that H+ concentration and C1complexation control dissolution of Pb-bearing minerals in the stomach and that both GI tract enzymes and organic acids are necessary to maintain Pb in the soluble form on entering the small intestine, The experimental results indicate that ingestion of Pb-bearing mine wastes results in limited Pb solubility and that the in vitro test provides a screening-level estimate of the maximum available Pb from mine wastes.
Long-term water balance investigations are needed to better understand hydrologic systems, especi... more Long-term water balance investigations are needed to better understand hydrologic systems, especially semi-arid mountainous catchments. These systems exhibit considerable interannual variability in precipitation as well as spatial variation in snow accumulation, soils, and vegetation. This study extended a previous 10-year water balance based on measurements and model simulations to 24 years for the Upper Sheep Creek (USC) catchment, a 26 ha, snow-fed, semi-arid rangeland headwater drainage within the Reynolds Creek Experimental Watershed in southwestern Idaho, USA. Additional analyses afforded by the additional years of data demonstrated that the variability between streamflow and annual precipitation (r 2 = 0.54) could be explained by the timing of precipitation and antecedent moisture conditions. Winter-spring precipitation and soil moisture deficit at the beginning of the water year accounted for 83% of the variability in streamflow, which was almost as accurate as applying the more complex physically-based Simultaneous Heat and Water (SHAW) numerical model (r 2 = 0.85) over the three dominant land cover classes. A conceptual model was formulated based on field observations, numerical simulations and previous studies. Winter precipitation and spring snowmelt must first replenish the deficit within the soil water profile and ground water system before water is delivered to the stream. During this period, surface water and ground water are tightly coupled and their interaction is critical to streamflow generation. Shortly after snow ablation, however, water flux in the root zone becomes decoupled from the ground water system and subsequent precipitation does little to contribute to streamflow for the current year, but serves to offset ET and the soil moisture deficit at the beginning of the following year. This study demonstrates the merits of long-term catchment-scale research to improve our understanding of how climate and land cover interact to control hydrologic dynamics in complex mountainous terrain.
Energy balance models use physically based principles to simulate snow cover accumulation and mel... more Energy balance models use physically based principles to simulate snow cover accumulation and melt. Snobal, a snow cover energy balance model, uses a flux-profile approach to calculating the turbulent flux (sensible and latent heat flux) components of the energy balance. Historically, validation data for turbulent flux simulations have been difficult to obtain at snow dominated sites characterized by complex terrain and heterogeneous vegetation. Currently, eddy covariance (EC) is the most defensible method available to measure turbulent flux and hence to validate this component of an energy balance model. EC was used to measure sensible and latent heat flux at two sites over three winter seasons (2004, 2005, and 2006). Both sites are located in Reynolds Creek Experimental Watershed in southwestern Idaho, USA and are characterized as semi-arid rangeland. One site is on a wind-exposed ridge with small shrubs and the other is in a wind-protected area in a small aspen stand. EC data were post processed from 10 Hz measurements. The first objective of this work was to compare EC- measured sensible and latent heat flux and sublimation/condensation to Snobal-simulated values. Comparisons were made on several temporal scales, including inter-annual, seasonal and diurnal. The flux- profile method used in Snobal assumes equal roughness lengths for moisture and temperature, and roughness lengths are constant and not a function of stability. Furthermore, there has been extensive work on improving profile function constants that is not considered in the current version of Snobal. Therefore, the second objective of this work was to modify the turbulent flux algorithm in Snobal. Modifications were made to calculate roughness lengths as a function of stability and separately for moisture and temperature. Also, more recent formulations of the profile function constants were incorporated. The third objective was to compare EC-measured sensible and latent heat flux and sublimation/condensation to the modified Snobal simulated values. The final objective was to determine if the modified turbulent flux algorithm in Snobal results in hydrologically significant improvements to simulations.
Proceedings 2011 IEEE International Conference on Spatial Data Mining and Geographical Knowledge Services, 2011
Digital elevation model (DEM) is one of the most important information that can be derived from t... more Digital elevation model (DEM) is one of the most important information that can be derived from the airborne LiDAR data. However in areas covered by dense vegetation, the chance of laser passing through the canopy, hitting the ground and back to the receiver is limited, thus it is difficult to achieve accurate DEM in regions with dense vegetative covers (trees, shrubs and grasses). We considered the challenges in deriving accurate terrain elevation information from LiDAR data: identifying areas covered with dense vegetation, separating LiDAR point clouds into ground and non-ground returns, interpolating to create raster surface models. A case study in the semi-arid mountainous area of the Northwest US shows that dense shrub caused about 20 cm DEM error in vertical accuracy, in line with similar study results of LiDAR derived DEM from dense grass areas. Terrain, cover type and LiDAR acquisition parameters (scan or incidence angle, point density) can also affect accuracy.
Radiation fields are required to model snow and hydrologic processes and properties over forested... more Radiation fields are required to model snow and hydrologic processes and properties over forested mountain regions. We present a method that utilizes a representation of terrain and forest structure (height, crown and trunk shape, canopy density and spacing) to modulate above-canopy solar and thermal radiation fields for canopy shading and emissivity effects. The method preserves gap fraction, and accounts for terrain features of slope, aspect and local horizon-induced terrain shading. The method is initiated over a very high resolution, pre-determined distribution of canopy crowns and gaps. For development of the method, terrain structure information was derived from a LiDAR representation of both terrain and canopy over the Fraser Experimental Forest in Colorado. The method can also be applied to an artificial canopy structure, based on a statistical distribution of canopy crowns and gaps as simulated over a region. Though the method is computationally expensive, once the shading and emissivity functions have been computed for a full range of azmuthal conditions, they can be retained in look-up tables, and scaled to an arbitrary set of radiation conditions. The method is applied over the LiDAR domain at the Colorado site using by correcting above-canopy radiation fields for a series of selected dates representing high and low sun angles, and a variety of snow depth conditions.
The impacts of timber harvesting practices on the flow regime, water and isotope mass balance (2H... more The impacts of timber harvesting practices on the flow regime, water and isotope mass balance (2H, 2O) in a mountainous catchment were studied over the period from 2004 to 2007. The Mica Creek Experimental Watershed (MCEW) is located in northwestern Idaho, USA (97 km2, 975 - 1,750 m a.s.l.). It includes three sub watersheds of comparable physical conditions with clear-cut (100 % removal in 50 % of the area, CC), partial-cut (50 % removal in 50 % of the area, PC), and unimpacted (control forest, CF) sites. Precipitation, spring water, stream flow, soil water, and sap flow were collected for stable isotope analyses on a monthly basis during the growing season. Snow, which is the dominant water input in this region, was intensively studied during winter 2005/06. A base flow sampling campaign was conducted during low flow in September 2006. Weekly analyses of precipitation indicate isotopic variations ranging between -3.9 ‰ and -22.0 ‰ and -42 ‰ and -170 ‰ for δ2O and δ2H, respectively. Isotopic composition of snow samples obtained in 2006 from snow profiles at snow courses varied between -13.8 ‰ and -17.5 ‰ for δ2O and δ2H values varied between -102 ‰ and -129 ‰. The isotopic composition of snow reflects enrichment due to intercepted snow sublimation and evaporation in the dense forest sites. Stream flow samples are in the range of -15.7 ‰ and -113 ‰ for δ2O and δ2H, respectively. Mean soil water concentrations of the upper 20 cm for the CC, PC and CF sites show values of -15.4 ‰, -14.1 ‰, -13.3 ‰ and -123 ‰, -114 ‰, -109 ‰ for δ2O and δ2H, respectively. Sap flow appeared to reflect differential canopy interception losses, with greater enrichment under the densest canopies (-14.4 ‰, -14.2 ‰, -13.8 ‰ for δ2O of CC, PC, CF and -130 ‰, -124 ‰, -119 ‰ for δ2H of CC, PC, CF, respectively). Presumably, variations reflect fluctuating rates of precipitation, deposition, ablation and sublimation of the snow cover. Stream water, soil water and plant water follow these patterns indicating that water isotope concentrations vary throughout physiographically similar areas as a result of land cover differences. Water isotope fluxes were calculated and allowed improved estimates of evapotranspiration of the forest treatments.
The turbulent exchange of sensible and latent heat and mass between the snowcover and the atmosph... more The turbulent exchange of sensible and latent heat and mass between the snowcover and the atmosphere can represent a significant component of the snowcover energy and mass balance in mountainous environments. These fluxes are computed in land surface and energy balance snowmelt models, though few measurements exist for comparison or validation. Where measurements do exist, they employ eddy covariance (EC) instrumentation. Two outputs are generated with typical eddy covariance instrumentation: time series data, which is later corrected and fluxes calculated, and 30-minute flux summaries, which are calculated directly without correction. Due to data storage limitations, the flux summaries are often stored instead of raw time series data. More commonly, turbulent fluxes are modeled from slow response meteorologic data. This research considers data taken from within a forested site over snow in order to compare turbulent fluxes estimated from the two eddy covariance output types and modeled turbulent fluxes. Preliminary results indicate corrected time series fluxes are approximately 15%-20% smaller than 30-minute flux summaries, and approximately equivalent to the modeled fluxes at this site. The conditions under which the labor-intensive time series corrections are mandatory are described. Also, the conditions under which the 30-minute flux summaries and modeled fluxes are similar to time series estimated turbulent fluxes are described. The steps used to process, correct, and analyze (including co-spectra) the time series eddy covariance data are presented. The data used in this analysis are from a uniform conifer stand during the winter of 2003 as part of the Cold Lands Processes Field Experiment (CLPX). This research improves our understanding of how measurements of turbulent fluxes vary by estimation method and sets the stage for improved modeling of turbulent fluxes.
Long-term water balance investigations are needed to better understand hydrologic systems, especi... more Long-term water balance investigations are needed to better understand hydrologic systems, especially semi-arid mountainous catchments. These systems exhibit considerable inter-annual variability in precipitation as well as spatial variation in snow accumulation, soils, and vegetation. Long-term studies that capture a wide range of conditions can be used to gain insight into potential future hydrologic regimes. This study used the Simultaneous Heat and Water (SHAW) model to quantify the hydrological fluxes over 24 years at the Upper Sheep Creek catchment, a 26 ha, snow-fed, semi-arid headwater drainage within the Reynolds Creek Experimental Watershed in southwestern Idaho, USA. The quantity of data afforded by the 24-year study allowed a more complete conceptual model of the system to be developed, and detailed analyses of both inter- and intra-annual flow variations. In this system, winter precipitation and spring snowmelt must first replenish the deficit within the soil water profile and ground water system before water is delivered to the stream. During this period, surface water and ground water are tightly coupled, and their interaction is critical to streamflow generation. Shortly after snow ablation however, water flux in the root zone becomes decoupled from the ground water system and subsequent precipitation does little to contribute to streamflow for the current year. Data indicated that relatively wet years characterized by drier winter and wetter spring months exhibited lower runoff ratios compared to relatively dry years with early snowmelt which exhibited higher runoff ratios. The former case appears to be due to less spatially variable precipitation due to reduced snow distribution and late-season replenishment of the soil moisture reservoir during the growing season. These dynamics suggest that projected future climate conditions characterized by stable or increased precipitation and increased rain/snow ratios may exhibit lower annual water yields due to increased evaporative fractions. This interpretation is supported by simulations of projected flow regime changes at a nearby forested watershed using downscaled GCM data, which indicate increased winter and spring evapotranspiration and declining annual hydrologic yields.
In the Pacific Northwest (PNW), concern about the impacts of climate and land cover change on wat... more In the Pacific Northwest (PNW), concern about the impacts of climate and land cover change on water resources and flood-generating processes emphasize the need for a mechanistic understanding of the interactions between forest canopies and hydrological processes. A detailed measurement and modeling program in the 1999 and 2000 hydrologic years characterized hydrological processes in a 500-600 year old Douglas fir-western hemlock seasonal temperate rainforest. The measurement program included sub-canopy arrays of radiometers, tipping bucket rain gauges, and soil temperature and moisture probes, to supplement a vertical temperature and humidity profile within the forest canopy. The measurements were used to modify the Simultaneous Heat and Water (SHAW) Model for application in forested systems. Changes to the model include improved representation of interception dynamics, stomatal conductance, and within- canopy energy transfer processes. The model was calibrated for the 1999 hydrologic year, and validated for the 2000 season. The model effectively simulated canopy air and vapor density profiles, snowcover processes, throughfall, soil water content profiles, shallow soil temperatures, and transpiration fluxes for both years. The largest discrepancies between soil moisture and temperature were observed during periods of discontinuous snowcover. Soil warming at bare locations was delayed until most of the snowcover ablated due to the large heat sink associated with the residual snow patches. During the summer, simulated evapotranspiration decreased from a maximum monthly mean of 2.17 mm day-1 in July to 1.34 mm day-1 in September, as a result of decreasing soil moisture and declining net radiation. Our results indicate that a relatively simple parameterization of the SHAW model for the vegetation canopy can accurately simulate seasonal hydrological fluxes in this environment. The model could be used to assess the potential effects of climate or landcover changes on hydrological processes in PNW old-growth ecosystems. Application and validation of the model in other forest systems will establish similarities and differences in the interactions of vegetation and hydrology, and assess the sensitivity of other systems to natural and anthropogenic perturbations. >http://ucs.orst.edu/~linkt/wrccrf/index.html</a>
Sensible and latent heat and mass flux represent a significant component of the snowcover energy ... more Sensible and latent heat and mass flux represent a significant component of the snowcover energy and mass balance in mountain environments. Though these fluxes are computed in energy balance snow models, limited measurements exist for comparison or validation in complex, mountainous sites. Sensible and latent heat and mass flux can be determined directly from the turbulent fluctuations measured by fast-response sensors using eddy covariance (EC) theory. Two EC study sites, which are operated through the winter, were located in southwestern Idaho in a small headwater catchment of the Reynolds Creek Experimental Watershed, located approximately 80 km southwest of Boise, Idaho. One, a protected, below canopy site is located within a stand of aspen trees, and the other, an exposed site, is located nearby on a ridge over mixed sagebrush. Corrections and post-processing of eddy covariance data are discussed and EC-measured fluxes from the two sites are compared to better understand the manner in which terrain and vegetation influence turbulent fluxes over snow. Turbulent fluxes are also modeled at these two sites using the Snobal energy balance snow model, and differences between simulated and measured fluxes are evaluated. This research will improve our understanding of how heat and mass flux from the snowcover impacts water resources in areas dominated by, high winds, complex terrain and variable vegetation conditions, provide validation data for snow models, and ultimately improve water supply forecasts required for management decisions.
In mountainous, forested environments, snowcover dynamics exert a strong control on hydrologic an... more In mountainous, forested environments, snowcover dynamics exert a strong control on hydrologic and atmospheric processes. Snowcover ablation patterns in forests are controlled by a complex combination of depositional patterns coupled with radiative and turbulent heat flux patterns related to topographic and canopy cover variations. Quantification of small-scale variations of radiant energy in forested environments is necessary to understand how canopy structure affects snowcover energetics to improve spatially-explicit physically-based snowmelt models. Incoming solar and thermal radiation patterns were measured during the melt season around individual trees in isolated deciduous and coniferous forest patches. During clear to partly cloudy conditions, solar radiation around the leafless deciduous tree was reduced by 68%, whereas thermal radiation was enhanced by 26%. Under similar meteorological conditions, solar radiation was reduced by 87% and thermal radiation was enhanced by 43% beneath the crown of the coniferous tree. To assess potential impacts of radiative differences between open and sub-canopy net snowcover radiation, a simple analysis of sensitivity of net snowcover radiation to a range of snowcover albedo values was completed. For the meteorological conditions during this study, the analysis indicates that the deciduous canopy is likely to have a minor impact on net radiation differences. The area beneath the coniferous crown is expected to exhibit enhanced net radiation for relatively high (>0.6) open site albedo values. A small forest gap is expected to exhibit minimal difference relative to open sites for typical albedo values, whereas a large gap is expected to exhibit less net radiation than open areas. During cloudy to overcast conditions, net radiation at all canopy locations is expected to be lower than at open sites. These net radiation differences coupled with decreased turbulent fluxes due to lower wind velocities and reduced snow water equivalent values due to canopy interception losses help to explain small-scale patterns of snowmelt in non-uniform forested areas. This work also emphasizes the need to consider canopy heating in sparse forest and edge environments and to develop an improved understanding of sub-canopy snowcover albedo patterns and dynamics.
Sensible and latent heat and mass fluxes can represent a significant component of the snowcover e... more Sensible and latent heat and mass fluxes can represent a significant component of the snowcover energy and mass balance in mountain environments. Though these fluxes are computed in energy balance snow models, few measurements exist for comparison or validation. This research investigates the methodology required and problems associated with the direct measurement of sensible and latent heat flux over snow. The sensible and latent heat and mass fluxes can be determined directly from the turbulent fluctuations measured by fast-response sensors using eddy covariance (EC) theory. The general site considerations and specific weather conditions common to mountain catchments that affect EC data collection over snow is explored. Corrections and post-processing of eddy covariance data is discussed. Examples from established EC measurement sites under adverse and optimal conditions will be presented. The two primary EC study sites are located in southwestern Idaho in a small headwater catchment of the Reynolds Creek Experimental Watershed, located approximately 80 km southwest of Boise, Idaho. A protected, below canopy site is located within a stand of aspen trees, and an exposed site is located on a ridge over big mountain sagebrush. The study investigates the conditions under which EC instrument systems can be used in mountainous, snow-dominated environments, the processing required to prepare the data for analysis, and several examples of post-processed data collected over snow. This research will improve our understanding of how heat and mass flux from the snowcover may impact water resources under the variable and changing climate conditions so common in the Western US.
Forest canopies strongly affect the radiation balance of snowcovers by reducing solar radiation a... more Forest canopies strongly affect the radiation balance of snowcovers by reducing solar radiation at the snow surface, decreasing the snow surface albedo, and enhancing incoming thermal radiation at the snow surface relative to open areas. During radiation-driven snowmelt, thermal radiation is commonly the dominant component of melt energy in forests. The relative importance of solar and thermal radiation for snowmelt
A suite of detailed experimental measurements and modeling are used to evaluate how snow distribu... more A suite of detailed experimental measurements and modeling are used to evaluate how snow distribution and melt are influenced by vegetation and topographic structure across different experimental catchments in western North America (two in the western US, and one in western Canada). Critical interactions between vegetation, topography and snowcover in snow-dominated basins are investigated to evaluate how these differences impact
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