Evaporation is an important component of hydrological cycle. Estimating evaporation using conversional meteorological data is still a very useful approach for studying long-term evaporation trends given the large amount of available datasets. However, improving the accuracy of the approaches, which use conventional meteorological data to estimate evaporation, is still challenging due to their applicability in different surfaces and different locations. In this study, we evaluate eight approaches, which are frequently used for evaporation estimation, using our comprehensive datasets over an open water surface in Mississippi, U.S.A.

The research site is located in the Rose Barnett Reservoir (32o26'N, 90o02'W), Mississippi, U.S.A. The total area of the reservoir is about 33,000 acre. The eddy covariance tower was set up in the middle of the reservoir with its fetch exceeding 1.5 km in all directions. The water depth is about 4 m around the tower location. The tower with its height of 4 m stands over a stable wood platform with its size of 3 m × 3 m and height of 1 m above the water surface. The eddy covariance system on the tower is used to measure fluxes of sensible heat, latent heat, and CO2. Besides the fluxes, microclimate data are also measured, including wind speed, wind direction, solar radiation, net radiation, air temperature and relative humidity at four levels, water surface temperature, and water temperature at six depths.

We use these data (four months in August, September, October, and November) to validate eight methods for estimating evaporation. These eleven methods include Jansen-Haise, Penman, Mass transfer, DeBruin-Keijman, Priestley-Taylor, Hamon, DeBruin, and Brutsaert-Stricker,. We will report the mean and standard deviation of the differences between eddy covariance values and the values from the eight equations under different weather conditions. We will analyze fundamental causes leading to the bias in estimating evaporation. Some empirical parameters in the equation will be examined and possible medications and improvements may be made to reflect the environmental controls on the evaporation.