Evaporation

Abstract

Evapotranspiration is the most important term among the “sink” terms of the soil-water balance equation. In this chapter are described contemporary methods for evapotranspiration estimation, as well as the calculation methods to estimate its structural components: evaporation and transpiration. The basic equations of potential evapotranspiration calculation (the Penman equation) and actual evapotranspiration calculation (the Penman–Monteith equation) are presented, and their applications are described. The FAO modification of the Penman–Monteith equation to evaluate daily and hourly reference evapotranspiration is also presented. This chapter also contains the most popular empirical equations for the calculation of the potential evapotranspiration of various evaporating surfaces. Results of measurements of root-extraction patterns and proposed calculation methods for root water-uptake functions needed in mathematical models are briefly discussed.