*3.4.2 Temperature effect*

Temperature variation between stations shows a period of high temperatures, spanning from June to October, which can cause scalding due to increased transpiration. Periods of low temperatures, from November to February, are the cause of the intensity of winter frosts which can result in vegetative damage such as necrosis. This indicates by Floret & Pontanier [49, 50], the highly contrasted thermal regime is affected by a strong potential evapotranspiration.

### *3.4.3 Wind effect*

Winds are very frequent and violent in the study area, which significantly contributed to the increase in evapotranspiration. According to Escadafal [51], the often strong winds further exacerbate evaporative demand. Khader [52] indicates that wind is a very drying climatic parameter that influences PET by increasing the temperature and simultaneously lowering the humidity of the air which causes it. It accelerates the desiccation of plants, and the increase of evapotranspiration. In the case of the hot and dry southerly "Sirocco" wind blows especially in summer, on average 200 times a year, and lasts more than 45 days a year, accentuating the dry season and bringing back appreciable quantities of sand. This wind causes the soil to dry out by causing a strong evapotranspiration of the plants [53].

### *3.4.4 Effect of rainfall*

According to Derouiche [54, 55], the decrease in rainfall and the increase in temperature represent unfavorable factors for both the soil and the plant. Precipitation cannot compensate for the intense evapotranspiration to which vegetation is subjected during the summer season. The deficit is only made up by the soil's water reserves according to its capacity to store the precipitation it receives.

#### **3.5 Effect of evapotranspiration on plants of steppe**

In the arid region of Naâma, the steppe plants are characterized by a low quotient of potential Precipitation/Evapotranspiration. Thus, the potential evapotranspiration is very high due to heat and sunshine, so rain is especially needed when evapotranspiration is high and precipitation is not sufficient for the normal development of the plant.

The decrease of evapotranspiration leads to the change of the surface energy balance, to an increase of temperatures and to a decrease of the soils capacity to store water for vegetation. Evapotranspiration cools the air through the evaporation of water present in the soil and plants as well as transpiration in the leaves. The climatic aridity has a considerable influence on the growth of steppe plants, because vegetation modifies the water balance of the substrate where it grows, by taking water that is lost through transpiration [25].

Maximum temperatures accentuate water stress; in fact excessive heat causes dehydration resulting from accelerated perspiration. If the soil cannot provide sufficient water supply, there is a loss of turgor. In vegetation, potential transpiration increases with temperature and climatic drought. Therefore, vegetation can act as a brake on the diffusion of water vapor [55]. It helps reduce soil evaporation, reducing net radiation and reducing surface temperature [56]. Vegetation can also

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

decrease the amount of solar radiation reaching the soil and the temperature of the soil, which can significantly reduce evaporation compared to bare soil [57].

Stomatal regulation is influenced, degree of opening of the stomata depending on climatic factors of evapotranspiration. As soon as a water deficit occurs, the plant adjusts, quickly and reversibly by the process of transpiration, that is to say the water inputs, are carried out at a rate lower than the thermal needs of the plant, the flows of water which cross it by the closing of its stomata (small openings of the leaves, which regulate the gas exchanges between plant and atmosphere).

#### **3.6 Effect of steppe vegetation on evapotranspiration**

Plants then invest in "survival" by reducing the phenomena of evapotranspiration, photosynthetic leaf surfaces, in times of drought. It takes place at the level of the stomata of the leaves by reducing their exchange surfaces and closing their stomata. It turns out that vegetation can have an effect on different components of the water balance. As soon as the water conditions at the root level evolve towards drought, the leaves react by closing their stomata, at the same time reducing evaporation, which has the effect of increasing their surface temperature [55, 58]. Because water stress at the roots has a repercussions on the evapotranspiration regime of the leaves.

According to Le Houérou and Popov [59], the reduction in the maximum daily temperature (2.5°C) by woody vegetation corresponds to a decrease of about 147 mm/year of PET at ground level.

The woody tree cover (*Retama retam, Pistacia atlantica*) directly reduces solar radiation, air temperature and wind speed on the ground, which can reduced the potential evapotranspiration (PET). Indeed, the natures of the vegetation, woody species consume more water by evapotranspiration than herbaceous species.

Vegetation can increase evapotranspiration through transpiration. This can increase water loss through evapotranspiration. This explains by Carminati *et al.* [60], vegetation can influence evapotranspiration in several ways: vegetation can act on the energy state of soil water through transpiration, which has a linear relationship with the suction exerted by the xylem in dry soils.

According to Yagoub (2016) [54], vegetation regulates surface temperature by absorbing radiant energy and re-emitting it as latent heat via the process of evapotranspiration. Among the regulatory mechanisms, plants are reacted by the reduction of aerial organs to reduce the evaporating surface and the taking of reduced forms (reduction of the leaf system, thorns, hairs, etc.) and the distribution and arrangement of the leaves of a plant structure can act on climatic parameters linked to evapotranspiration (wind speed, solar radiation). In fact, in the underground part, the root system can play a more important role than that of the hydrogeological properties in the useful water reserve.

#### **3.7 Mechanism of adaptation and acclimatization of steppe vegetation**

Due to the intensity of evaporative transpiration, the steppe vegetation adapts to withstand the harsh climatic conditions. The difficult climatic conditions, in this steppe area, allow the vegetation to develop an adaptation system for its maintenance and survival. These ecophysiological relationships can largely explain the adaptation of steppe species to the arid Mediterranean climate. Despite the very harsh and very restrictive environmental conditions, there are still geomorphological zones offering more or less favorable conditions for the survival and proliferation of a characteristic spontaneous flora adapted to climatic hazards. These adaptations have shown that steppe vegetation adapted to ecological stress uses one or more mechanisms to compensate for the inadequate water balance and mitigate the effect of water deficit. They cover the physiological and morphological regulations that allow plants to adapt to a deficient water supply occurring at different scales [61].
