Clearing your Desk! Software and Data Services for Collaborative Web Based GIS Analysis

David Tarboton is a professor at Utah State University. This presentation was given as part of the GIS Day@KU symposium on November 18, 2015. For more information about GIS Day@KU activities, please see http://www.gis.ku.edu/gisday/2015/.Platinum Sponsors: KU Department of Geography and Atmospheric Science; KU School of Business. Gold Sponsors: Bartlett & West; Kansas Biological Survey; KU Environmental Studies Program; KU Institute for Policy & Social Research; KU Libraries. Silver Sponsors: State of Kansas Data Access and Support Center (DASC). Bronze Sponsors: KU Center for Remote Sensing of Ice Sheets (CReSIS); TREKK Design Group, LLC; Wilson & Company, Engineers and Architects

Measurements and Modeling of Snow Energy Balance and Sublimation from Snow

Snow melt runoff is an important factor in runoff generation for most Utah rivers and a large contributer to Utah\u27s water supply and periodically flooding. The melting of snow is driven by fluxes of energy into the snow during warm periods. These consist of radiant energy from the sun and atmosphere, sensible and latent heat transfers due to turbulent energy exchanges at the snow surface and a relatively small ground flux from below. The turbulent energy exchanges are also responsible for sublimation from the snow surface, particularly in arid environments, and result in a loss of snow water equivalent available for melt. The cooling of the snowpack resulting for sublimation also delays the formation of melt runoff. This paper describes measurements and mathematical modeling done to quantify the sublimation from snow. Measurements were made at the Utah State University drainage and evapotranspiration research farm. I attempted to measure sublimation directly using weighing lysimeters. Energy balance components were measured, by measuring incoming and reflected radiation, wind, temperature and humidity gradients. An energy balance snowmelt model was tested against these measurements. The model uses a lumped representation of the snowpack with two state variables, namely , water equivalent and energy content relative to a reference state of water in the solid phase at 0 degrees Celcius. This energy content is used to determine snowpack average temperature or liquid fraction. The model is driven by inputs of air temperature, precipitation, wind speed, humidity and solar radiation. The model uses physically based calculations of radiative, sensible, latent and advective heat exchanges. An equilibrium parameterization of snow surface temperature accounts for differences between snow surface temperature and average snowpack temperature without having to introduce additional state variables. This is achieved by incorporating the snow surface thermal conductance, which with respect to heat flux is equivalent to stomatal and aerodynamic conductances used to calculate evapotranspiration from vegetation. Melt outflow is a function of the liquid fraction, using Darcy\u27s law. This allows the model to account for continued melt outflow even when the energy balance is negative. The purpose of the measurements presented here was to test the sublimation and turbulent exchange parameterizations in the model. However the weighing lysimeters used to measure sublimation suffered from temperature sensitive oscillations that mask short term sublimation measurements. I have therefore used the measured data to test the models capability to represent the overall seasonal accumulation and ablation of snow

The Source Hydrology of Severe Sustained Drought in th Southwestern U.S.

This paper considers the risk of drought and develops drough scenarios for use in the study of severe sustained drought in the Southwestern United States. The focus is on the Colorado River gbasin and regions to which Colorado River water is exported, especially southern California, which depends on water from the Colorado River as well as the four major rivers in northern California. Drought scenarios are developed using estimates of unimpaired historic streamflow as well as reconstructions of streamflow based on tree ring widths. Drought scenarios in the Colorado River are defined on the basis of annual flow at Lees Ferry. Possible spatial manifestations of the Colorado River drough scenarios for input into a Colorado River system simualation model are developed by disaggregating the Lees Ferry flow to monthly flows at twenty nine source locations required by the model. The risk, in terms of retun period, of the drough scenarios developed, is assessed using stochastic models applied to both the Colorado River basin and the comvined flow in four major California rivers. The risks of severe sustained drought occurring concurrently in the Colorado River basin and California is also assessed

A New Method for the Determination of Flow Directions and Contributing Areas in Grid Digital Elevation Models

A new procedure for the representation of flow directions and calculation of upslope areas using rectangular grid digital elevation models is presented. The procedure is based on representing flow direction as a single angle taken as the steepest downward slope on the eight triangular facets centered at each grid point. Upslope area is then calculated by proportioning flow between two downslope pixels according to how close this flow direction is to the direct angle to the downslope pixel. This procedure offers improvements over prior procedures that have restricted flow to eight possible directions (introducing grid bia) or proportioned flow according to slope (introducing unrealistic dispersion). The new procedure is more robust than prior procedures based on fitting local planes while retaining a simple grid based structure. Detailed algorithms are presented and results are demonstrated through test examples and application to digital elevation data sets

Modeling the effect of vegetation of the accumulation and melting of snow

This work investigates the variability of snow accumulation and differences in the timing of melt and sublimation between open (grass/shrubs) and forest (conifer/deciduous) locations at a mountain study site in the Western US, using a combination of field observations and modeling. Observations include continuous automated climate and snow depth measurements supported by periodic field measurements of snow water equivalent and temperature in four different vegetation classes (grass, shrubs, coniferous forest, deciduous forest) at the TW Daniel Experimental Forest located 30 miles N-E of Logan. The Utah Energy Balance physically based snowmelt model, was enhanced by adding new parameterizations of: i) snow interception and unloading; ii) transmission of radiation through the canopy; and iii) atmospheric transport of heat and water vapor between the snow on the ground, intercepted snow in the canopy and the atmosphere above; to better simulate snow processes in forested areas. The enhanced model was evaluated by comparing model simulations of meteorological conditions (temperature, wind, radiation) and snow properties (water equivalent, depth, temperature) in and beneath the canopy with observations. Observations showed approximately 10 to 20% more snow accumulation in open areas compared to forest areas. Ablation rates were also found to be higher in open areas than in forest areas. In comparison to coniferous forest, deciduous forest had high rates of accumulation and ablation. The model performed well in representing these effects based on inputs such as canopy height, canopy coverage, leaf area index and leaf orientation; thereby improving our ability to simulate and predict snow processes across heterogeneous watersheds. (KEYWORDS: snow accumulation, melt timing, sublimation, interception, snowmelt

Canopy Radiation Transmission for an Energy Balance Snowmelt Model

To better estimate the radiation energy within and beneath the forest canopy for energy balance snowmelt models, a two stream radiation transfer model that explicitly accounts for canopy scattering, absorption and reflection was developed. Upward and downward radiation streams represented by two differential equations using a single path assumption were solved analytically to approximate the radiation transmitted through or reflected by the canopy with multiple scattering. This approximation results in an exponential decrease of radiation intensity with canopy depth, similar to Beer\u27s law for a deep canopy. The solution for a finite canopy is obtained by applying recursive superposition of this two stream single path deep canopy solution. This solution enhances capability for modeling energy balance processes of the snowpack in forested environments, which is important when quantifying the sensitivity of hydrologic response to input changes using physically based modeling. The radiation model was included in a distributed energy balance snowmelt model and results compared with observations made in three different vegetation classes (open, coniferous forest, deciduous forest) at a forest study area in the Rocky Mountains in Utah, USA. The model was able to capture the sensitivity of beneath canopy net radiation and snowmelt to vegetation class consistent with observations and achieve satisfactory predictions of snowmelt from forested areas from parsimonious practically available information. The model is simple enough to be applied in a spatially distributed way, but still relatively rigorously and explicitly represent variability in canopy properties in the simulation of snowmelt over a watershed