Evaporation from Water Surfaces

This chapter describes some U.S. studies on estimating evaporation from water bodies. Particular emphasis is on practical procedures and techniques to estimate evaporation from water surfaces using pan evaporation, available weather data, or new data collected specifically for estimating daily evaporation. This chapter describes several methods commonly used to estimate evaporation from water surfaces and discusses their strengths, weaknesses, data requirements, and relative accuracies. The methods include pan evaporation, water budget procedure, aerodynamic method, energy balance method, and a combination of the aerodynamic and energy balance procedures. The chapter then presents results of example applications of the combination method and the aerodynamic and Bowen ratio methods for a shallow lake, a deep lake, a river-reservoir system, and a reservoir where advection of energy is small. The examples illustrate various means of independent checks and assessment.