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United States Department of Agriculture

Agricultural Research Service

Title: Estimation of Evapotranspiration over the San Pedro Riparian Area with Remote and in Situ Measurements

Authors
item Qi, Jiaguo
item Moran, Mary
item Goodrich, David
item Marsett, R - USDA-ARS, USWCL AZ
item Scott, R - UNIV OF ARIZONA
item Chehbouni, A - ORSTOM/IMADES, HERMOSILLO
item Schaeffer, S - UNIV OF ARIZONA
item Schieldge, J - JET PROP LAB PASADENA CA
item Williams, D - UNIV OF ARIZONA

Submitted to: American Meteorological Society
Publication Type: Proceedings
Publication Acceptance Date: March 15, 1998
Publication Date: N/A

Interpretive Summary: The scarcity of water in arid and semi-arid regions makes it the most precious natural resource to man, animals, and plants. The ever increasing demands of a growing population and the continued use of water in commercial endeavors such as agriculture and mining are reducing available water supplies faster than they are being replenished. In order to insure a continued supply of this resource for use in crop and livestock production, it is necessary to understand all the forces involved in consuming water so informed decisions can be made about how to manage this resource. Once rainfall occurs or snow pack melts, the water will flow away as runoff, infiltrate into the soil, or evaporate. Precise measurements of surface runoff and infiltration can be easily made, but the evaporative loss is more difficult to measure. In this study, we developed a simple and practical technique to use aerial imagery or satellite imagery y(remote sensing imagery) and ground-based measurements to map the area and time distribution of evaporative loss of water over the natural vegetation of a riparian (stream side) corridor. This technique uses the difference between the surface temperature of the plants and the surrounding air temperature to calculate the water loss rate. The result is that the amount of water used by the plants of a large area can be measured without using labor intensive methods. With this ability to efficiently measure water use by plants over large areas, policy makers will be better informed when making decisions concerning the use of this resource. The impact for science is an improvement in the understanding of the volume of water used by the natural plant communities, which will improve the accuracy of water use models.

Technical Abstract: Water loss through plant transpiration is an important part of the water budget equation in arid and semi-arid regions. Because of significant differences in evapotranspiration (ET) rates among diverse components, estimation of spatial and temporal ET over heterogeneous areas has been a major challenge. In this study, measurements of ET from individual surface components were combined with remotely sensed images to develop approaches to estimate water losses through evapotranspiration. Data acquired include in situ ET measurements over three major vegetation types (cottonwood trees, mesquite shrubs, and sacaton grasses) and remote sensing images in April, June, and August 1997. The remote sensing images were first used to estimate the aerial extent of individual components, and then individual in situ ET measurements were correlated to the differential temperature (defined as surface temperature, Ts, minus air temperature, Ta). This correlation was then applied to maps of Ts-Ta derived from remotely sensed iamges and meteorological instrumentation to estimate the total amount of water loss through evaportranspiration. Results obtained using this approach indicate that the remote sensing imagery can be effectively used in mapping ET rates for heterogeneous surfaces. The estimated ET with remote sensing techniques resulted in comparable ET estimates with Bowen ratio, Scintillometer, and 3-D sonic devices. This study indicated that the total mount of water lost via evapotranspiration was estimated to be 48270 tons on a daily basis.

Last Modified: 10/1/2014
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