**1. Introduction**

The South Oranian steppe of Naâma is characterized by sparse vegetation and only drought tolerant plants that can live there. The steppe vegetation is therefore made up of open grassy formations, revealing bare soil between the plants and the amount of existing plant matter per unit area and roughly proportional to the precipitation received [1]. They are plant formations of a steppe character, primary or secondary, low and open in their typical physiognomy, and mainly subservient to arid and desert areas (rainfall <350 mm) [2].

Soil, vegetation and atmosphere form a single continuous system in which water circulates at a negative energy gradient, water moves throw the soil and then absorbed by roots, and from branches to leaves and then evaporated into intercellular cavities of leaves, and then diffused through the stomata to the layer of calm air in contact with the surface of leaves and finally to the outside atmosphere [3]. In the water cycle, water inputs correspond to precipitation and water losses are due to evapotranspiration, runoff and infiltration. Therefore, part of the precipitation can be intercepted by vegetation and returned to the atmosphere by evapotranspiration (ET) or sublimation [3].

Evapotranspiration is defined as "the response of vegetation to natural climatic conditions in relation to the physiological properties of the plant and its water resources. It is a complex climatic parameter, knowledge of which has significant practical interest at the moment of the estimation of water reserve of soils and of water requirements of crops and vegetation, and in the estimation of the volumes of water necessary for the development of plants. Evapotranspiration is also an indicator of interest in studies concerning climate change [4]. Evapotranspiration can act on the water balance and modify its various components through vegetation. Also, evapotranspiration plays a key role in the evaluation of the climatic capacities of a given region and is considered to be the indicator of optimal vegetation development [5].

This study aims to estimate the evapotranspiration in this region, and evaluate its impact on vegetation, in order to better understand the adaptation of this vegetation on this arid climate. In this chapter, we begin to present the basic concepts relating to the notions of water balance, the phenomenon of evapotranspiration and the methods of its evaluation. Next, we will describe the general characteristics of the steppe environment of the Naâma region (geographic location, climate, natural resources, etc.), then we will present the methodology adopted to achieve the study objectives, as well as, the impact of the evapotranspiration on vegetation. Finally, we end this work with a conclusion and some recommendations.

#### **1.1 Theoretical framework on evapotranspiration**

#### *1.1.1 Notions of evapotranspiration*

Evapotranspiration can be defined as the loss of water through soil and plant surface, usually expressed in mm/day. Indeed, the term "evapotranspiration" (ET) *Biophysical Effects of Evapotranspiration on Steppe Areas: A Case Study in Naâma… DOI: http://dx.doi.org/10.5772/intechopen.97614*

designates the water losses of a plant cover depending on the soil water reserve, the stage of vegetation development and the atmospheric environment [6]. Evapotranspiration is a combination of two terms, namely, evaporation (from a surface, from a body of water), and transpiration (from plants). It constitutes a fundamental characteristic of the climate, represents the cumulative evaporation of the soil and the transpiration of plants [7].

Evapotranspiration is a combination of two processes:

