Abstract

One of the most important components of the Everglades (south Florida) water budget is evapotranspiration (ET). In this area, most rainfall is likely returned to the atmosphere by ET. A study to quantify and model ET in the Everglades was begun in 1995. A network of nine ET-evaluation sites was established that represents the varied hydrologic conditions and vegetative characteristics of the Everglades. Data from continuous measurements of parameters for evaluation of ET at the sites for the period January 1996 through December 1997 were used to develop regional models that can be used to simulate ET at other times and places throughout the Everglades.

The Bowen-ratio energy budget method was selected for the ET evaluation. After careful screening to eliminate erroneous data, site and regional models of ET were calibrated for the nine sites. A modified Priestley-Taylor model of ET was calibrated for each site. In these models the Priestley-Taylor coefficient () was expressed as a function of incoming solar energy and water level. The individual site models were then combined into two regional models: one is applicable to vegetated wet-prairie and sawgrass-marsh sites in the natural Everglades system, and the other is applicable to freshwater sloughs and other open areas with little or no emergent vegetation.

Computed ET totals for all nine sites ranged from 42.78 inches per year at a sometimes-dry sparse-sawgrass site to 55.54 inches per year at an open-water site. Differences in annual ET relate to water availability and perhaps to density of vegetation.

The annual total ET values simulated by the regional models generally are in relatively close agreement with the computed values. The difference between computed and simulated ET generally was less than 3 inches per year. The median difference was about 1.4 inches per year.