Introduction

Abstract

Evaporation from open water and wet surfaces and evapotranspiration from vegetation are one of the major parameters in the hydrologic cycle. Most precipitation is lost in the form of evaporation and evapotranspiration with the percentage varying from region to region globally. Spatial variation by latitude, longitude, altitude, environment, and specific site conditions is a source of variation in evaporation and potential evapotranspiration. Standardized measurement and estimation of this parameter are challenging. Even with estimation methods standardized, variation in estimates would occur due to lack of uniformity in input data collection and quality control. A positive characteristic of this parameter is that it has relatively smaller variation for a given time and location. Seasonal fluctuations are known, and ranges are limited when water is not a limiting factor. Estimation error is relatively lower if appropriate equation and good quality input data is used for a given site.