**1.4 Methods used for the estimation of evapotranspiration**

Evapotranspiration is an important component of the water balance, involving both physical and biological processes. Many methods used for the estimation of evapotranspiration, which have been proposed by different authors. Each method is distinguished by the parameters taken into consideration, by the climatic conditions in which it was developed and by its application limits. Evapotranspiration can be evaluated by several methods (direct and indirect), which take into account

**Figure 1.** *Different streams of the water balance.*

*Biophysical Effects of Evapotranspiration on Steppe Areas: A Case Study in Naâma… DOI: http://dx.doi.org/10.5772/intechopen.97614*

different meteorological parameters (climatic, energetic) in relation to soil and vegetation parameters. In the meteorological stations of Naâma region, the evapotranspiration is measured directly with the lysimeter and evaporation pan and is estimated indirectly by using methods (equations) such as those of Thornthwaite, (1944), Penman (1948), Turkish (1961), etc.
