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Title: METHODS TO AGGREGATE TURBULENT FLUXES OVER HETEROGENEOUS SURFACES: APPLICATION OF SALSA DATA SET IN MEXICO 1361

Author
item CHEHBOUNI, A. - IRD/IMADES, MEXICO
item WATTS, C. - IMADES, MEXICO
item KERR, Y. - CESBIO, FRANCE
item DEDIEU, G. - CESBIO, FRANCE
item RODRIGUEZ, J. - IMADES, MEXICO
item SANTIAGO, F. - IMADES, MEXICO
item CAYROL, P - CESBIO. FRANCE
item BOULET, G. - IRD.IMADES, MEXICO
item Goodrich, David - Dave

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2000
Publication Date: 12/13/2000
Citation: N/A

Interpretive Summary: INTERPRETIVE SUMMARY Arid and semiarid 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. The amount of energy reaching the earth from the sun and leaving the earth's surface is a very important factor in how much, and how fast, water is evaporated from the earth's surface or transpired through plants and into the surrounding air. Measuring components of this energy over large areas with very different vegetation types is very difficult. One method to approach this problem is to use land surface temperatures measured from orbiting satellites. This requires developing relationships between the observed surface temperature and the energy components. In this study, three relationships, developed to work over a small area, ranging from simple to complex, were examined using data acquired in Sonora, Mexico as part of an interdisciplinary semiarid experiment. It was found that the simple and complex method worked relatively well but the intermediate method, which used remotely sensed data, did poorly. These results point to the need for finding appropriate relationship between surface temperature and energy components over large areas directly and not scaling up small area methods. If done, this will enable better management of water resources in arid/semiarid areas and many other regions around the world.

Technical Abstract: ABSTRACT The issue of using remotely sensed surface temperature to estimate the area-average sensible heat flux over surfaces made up of different vegetated patches has been investigated. The performance of three aggregation procedures, ranging from physically based through semi- empirical, to entirely empirical has been assessed by comparing measured and simulated area-average sensible heat flux. The results show that the physically based scheme perform very well. The performance of the entirely empirical scheme was reasonable but that of the semi-empirical scheme, which actually takes full advantage of remotely sensed data, was very poor. This result suggests that unlike the case of surface fluxes, it is not appropriate to use relationships calibrated at a local/patch scale, for an application at a larger/grid scale just by scaling the parameters. Therefore, future research should be directed towards building robust relationships between model and observational variables directly at the large-scale.