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Title: THE SENSITIVITY OF ECOSYSTEM CARBON EXCHANGE TO SEASONAL PRECIPITATION AND WOODY PLANT ENCROACHMENT 1779

Author
item POTTS, D. - UNIVERSITY OF ARIZONA
item HUXMAN, T. - UNIVERSITY OF ARIZONA
item Scott, Russell - Russ
item WILLIAMS, D. - UNIVERSITY OF WYOMING
item Goodrich, David - Dave

Submitted to: Oecologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2006
Publication Date: 9/6/2006
Citation: Potts, D.L., Huxman, T.E., Scott, R.L., Williams, D.G., Goodrich, D.C. 2006. The sensitivity of ecosystem carbon exchange to seasonal precipitation and woody plant encroachment. Oecologia 150(3): 453-463.

Interpretive Summary: Arid and semi-arid regions account for approximately one-third of the land mass of earth. These regions are experiencing continued pressure from population growth in many parts of the world. Water is a critical resource in these regions and is often in short supply. Detailed study of water resources and the hydrology of semi-arid regions is important if we are to continue to populate and use these regions. The Walnut Gulch Experimental Watershed, operated by the U.S. Dept. of Agriculture, Agricultural Research Service was established to observe and better understand water movement and the effects of land use on watershed hydrology in semi-arid regions. Our understanding of water and hydrology in semi-arid regions has been greatly enhanced through numerous studies of rainfall, runoff, and soil moisture patterns at this experimental watershed. In this study, an improved method to estimate surface soil moisture is developed using remotely sensed data obtained from an airplane. This method can also be applied to data obtained from orbiting satellites. The advantage of the newly developed method is that is allows estimation of surface soil moisture over smaller areas by combining information on surface temperature and local weather conditions. Soil moisture is important for a range of uses including seeding establishment, soil evaporation, runoff estimation, and mobility of vehicles for cross-country travel. All of these applications can be improved by having soil moisture data with higher spatial resolution derived from the methods developed in this study.

Technical Abstract: A downscaling method for microwave surface soil moisture is applied to PBMR data collected during the Monsoon ‘90 experiment. The downscaling method requires: (1) the coarse resolution microwave observations, (2) the fine-scale distribution of soil temperature, and (3) the fine-scale distribution of surface conditions composed of atmospheric forcing and the parameters involved in the modeling of land surface-atmosphere interactions. During the Monsoon ‘90 experiment eight ground-based meteorological and flux stations were operating over the 150 square kilometer study area simultaneously with the acquisition of the aircraft-based L-band PBMR data. The heterogeneous scene is hence composed of eight sub-pixels and the microwave pixel is generated by aggregating the microwave emission of all sites. The results indicate a good agreement between the downscaled and ground-based soil moisture as long as the intensity of solar radiation is sufficiently high to use the soil temperature as a tracer of the spatial variability of surface soil moisture.