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United States Department of Agriculture

Agricultural Research Service

Title: Modeling Evapotranspiration in a Sub-Tropical Climate

Authors
item Savabi, M
item Cochrane, T - VISITING SCIENTIST
item German, E - USGS
item Ikiz, Can
item Cockshutt, Nicholas

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 1, 2006
Publication Date: January 1, 2007
Citation: Savabi, M.R., Cochrane, T.A., German, E., Ikiz, C., Cockshutt, N.R. 2007. Modeling evapotranspiration in a sub-tropical climate. Journal of the American Water Resources Association.

Interpretive Summary: Evpotranspiration loss is estimated at about 80% of annual precipitation in south Florida. Accurate prediction of evpotranspiration is important during and beyond the implementation of the Comprehensive Everglades Restoration (CERP). In the USDA’s Everglades Agro-Hydrology Model (EAHM) the soil water intake is linked with the soil water redistribution, soil evaporation, plant transpiration, subsurface lateral flow and subsurface drainage to calculate daily root zone soil water content. Climate data from three sites with different soil and vegetal cover were used to evaluate the EAHM- Evapotranspiration routine. The results indicate that in a region such as south Florida that has two distinct dry and wet climate patterns with pronounced differences in humidity, wind, and rainfall, a combination method like Penman is a better prediction of daily ET. Also, in order to improve the predictability of the ET methods, more information about surface Albedo is needed about land surfaces with grass vegetation during the growing season.

Technical Abstract: Abstract: Evapotranspiration (ET) loss is estimated at about 80-85% of annual precipitation in South Florida. Accurate prediction of ET is an important part of the implementation of the Comprehensive Everglades Restoration Plan (CERP). In the USDA's Everglades Agro-Hydrology Model (EAHM), the daily soil root soil zone water content is calculated by linking the soil water intake to soil water redistribution, soil evaporation, plant transpiration, subsurface lateral flow and subsurface drainage. Hydrometeorological data from three sites with different soil moisture content were used to evaluate the EAHM-ET routine. At the site with standing water (Everglades), the EAHM water balance sub-model simulated the daily ET with acceptable accuracy using the Penman method. However, in the other areas with grass cover, there was a discrepancy between the model’s simulated values and the measured ET, using either Penman or the Priestly and Taylor method. The results indicate that in a region such as south Florida that has two distinct dry and wet climate patterns with pronounced differences in humidity, wind, and rainfall, a combination method like Penman is a better prediction of daily ET. Also, in order to improve the predictability of the ET methods, more information about surface Albedo is needed about land surfaces with grass vegetation during the growing season.

Last Modified: 9/20/2014
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