**1.3 Climatic factors influencing evapotranspiration**

According to Ferchichi (1996) [7], evapotranspiration is certainly closely linked to climatic factors, but it also depends on the natural environment of the region studied, the plant species concerned and soil properties. Evapotranspiration strongly depends on the availability of two factors: abiotic (climatic, geographic: topographic and orographic, hydrological and edaphic: soil) and biotic (biological: vegetation).

Evapotranspiration occurs under the influence of solar radiation, which is the source of energy that allows water to change from liquid to vapor. It depends on two elements: the heat supplied by solar radiation and the quantity of water available in the ground [20]. Evapotranspiration is certainly closely linked to climatic factors (evaporating power): air temperature, temperature of the earth's surface, wind speed and turbulence, duration of sunstroke or solar radiation, precipitation, relative air humidity and atmospheric pressure.

Indeed, the transpiration process depends on the following parameters: solar radiation, temperature, humidity, wind speed, the water vapor concentration gradient and therefore the water vapor pressure between the spaces substomatics of the leaf and the atmosphere, physiological mechanisms and metabolic activity of the plant, density of the root system, type of plant cover (structure, size, leaf area, presence or absence of leaves, nature of pigmentations, etc.). Finally, the process of evaporation depends on temperature, precipitation, air humidity and plant cover... (**Figure 1**).
