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Green River Basin Water Research
November 15, 2010 — Estimation of consumptive water use for irrigation is increasingly
important as demand for water resources increase and water supplies
become scarcer and/or more variable in time and space as a result of
both land use change and climate fluctuation. This is especially true in
semi-arid and arid regions like Wyoming. Historically, water use has
been estimated in irrigated lands by balancing surface water
models—irrigation water input minus runoff output was assumed to be a
reasonable estimate of water use by irrigators. But as discussions for
water rights become contentious, more accurate estimates of
evapotranspiration (ET) are needed.
Remote–sensing methods are increasingly employed in combination with modeling for evapotranspiration estimation because they can provide multi-temporal, spatially-distributed estimates of key variables based on spatially distributed measurement. The approach for estimating evapotranspiration with remotely sensed data couples thermal and optical remote sensing with energy balance models such as: SEBAL, Surface Energy Balance Algorithms for Land, and METRICtm, Mapping Evapotranspiration at high Resolution using Internalized Calibration.
Ground-based reference evapotranspiration in combination of the satellite imagery derived actual evapotranspiration are particularly significant in:
1) deriving crop coefficient for estimation of the daily actual evapotranspiration which can then be applied to estimate the seasonal variation of the consumptive use (ongoing research);
2) deriving root zone soil moisture maps (ongoing research); and
3) testing the validity of satellite-based approaches for estimating ET over large areas such as the entire Green River Basin in Wyoming.
This photo shows the experiment being conducted in cooperation with Steve Wolff of the Interstate Streams Division of the Wyoming State Engineer’s office. The experiment compares an eddy-covariance system against a large-aperture radiometer in both measuring evapotranspiration and verification of satellite methods for estimating ET over the Green River Basin. This experiment was conducted this summer in Duck Creek meadow west of Pinedale, and was managed by post-doctoral associate Dr. Nawa Pradhan. Scintillometers (pictured above) are set up at Duck Creek in Pinedale, courtesy photo’s.
Thus, to conduct the research and the applicability on the above mentioned points, faculty members Dr. Fred Ogden and Dr. Nawa Raj Pradhan set up ground-based metrological stations, eddy-covariance and large-aperture scintillometer in the Green River Basin, Pinedale, Wyoming.
Research data on the significance of the derived root zone soil moisture map in a distributed hydrological model will be presented by Pradhan et al. in a forth coming Remote Sensing and Hydrology 2010 Symposium, in Jackson, Wyoming. Scintillometers were installed on July 7, 2010, in the Duck Creek meadow, west of Pinedale and that research data will be shared at a later date.
The main challenge in the energy balance approach used by Ogden and Pradhan is to determine the partitioning of the available energy, the difference between net radiation and ground heat flux, into latent heat flux and sensible heat flux. The energy balance approach utilizes a linear relationship between sensible heat flux and the radiometric surface temperature for all pixel conditions, wet and dry. We will test the validity of this generalized empirical relationship in the completely wet pixel, Duck Creek meadow wetland, with the eddy-covariance and large-aperture scintillometer sensible heat flux. This test would also help in comparative analysis of the applicability of scintillometers in the wetland fingerprint spectral region with that at the dry land. We will contribute our part of this research in ‘Inter-Comparison of Large Aperture Scintillometers’ by Hendrickx et al., in the upcoming Remote Sensing and Hydrology Symposium.
Theories of hydrological processes are sought for applications in regional water resources planning, in the amelioration of water quality and quantity degradation in large river basins, in the validation of general circulation models (GCMs) and in the prediction of the hydrological impacts of global climate change. Scale problems arise naturally when seeking connections among physical processes at disparate scales in space and time. In our research, we are taking account of data from a range of scales; point scale data from the eddy covariance system, data from wider fingerprint spectral region of scintillometers and the satellite imagery pixel resolution of 30m and more. It is hoped that this research outcome will hint at the proper notions of scale transformation in seeking generalization across scales of a theory, especially energy balance theory in evapotranspiration estimates.
The 2008–09 research was sponsored by the State Engineer’s Office to study consumptive use of water in the Green River Basin. Although there was no funding this year, collaborative research continues using some funding from the US Army Research Office and equipment funding from the State of Wyoming and a grant from the U.S. Army Research Office. The laser scintillometer system is on loan from New Mexico Tech.