**3.3 Calculation of the hydrological balance and evapotranspiration, real evapotranspiration (RET) and flow deficit**

The results obtained from the calculation of evapotranspiration (PET, RET, EUR, Deficit) for the 3 stations are reported in **Table 11**.

#### *3.3.1 For the Mécheria station*

We notice that the PET greatly exceeds the precipitation (**Table 11**); and we observe the existence of two very distinct seasons. A surplus season during which rainfall is greater than or equal to the PET (December–February) and the deficit season from March to November. During the cold season, precipitation covers the needs of potential evapotranspiration and allows the formation of Easily Usable Reserve (EUR). From the month of March we have an exhaustion of the EUR which results in an agricultural deficit.

#### *3.3.2 For the Naâma station*

We note that from November the precipitation is greater than the evapotranspiration (R > PET) (**Table 12**). The Easily Usable Reserve (EUR) reaches its maximum in January, February and March. From the month of March, we record an agricultural deficit of 4.72 mm and which reaches its maximum in July with 181.05 mm. The annual deficit is estimated at 677.89 mm, and the actual evapotranspiration (RET) is equal to 207.93 mm or 95.05% of precipitation.

#### *3.3.3 For the Aïn Sefra station*

We see that precipitation is less than evapotranspiration throughout the year (R > PET) except in January when 15.65 mm of precipitation is recorded (**Table 12**, **Figure 6**). The Easily Usable Reserve (EUR) is zero throughout the year. We record an agricultural deficit throughout the year with a minimum of 3.07 mm in February and a maximum of 190.3 mm in July. The annual deficit is of the order of 746.43 mm. The actual evapotranspiration (RET) is equal to 194.53 or 97% of precipitation.


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


**Table 11.**

*Calculation of PET by the Thornthwaite method for the study stations (1990–2014).*

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


**Table 12.**

*Results of real evapotranspiration (RET) according to the Turkish method.*

#### **Figure 6.**

*Graphical representation of the water balance, mean monthly evapotranspiration according to Thornthwaite.*

Examination of the graphs (**Figure 6**) shows that on an annual scale, PET greatly exceeds precipitation and on a monthly scale, there are two very distinct seasons. a surplus season during which precipitation is greater than or equal to the ET from November to March and a deficit season from April to October. Potential (PET) and actual (RET) evaporation vary considerably between ecosystems and sometimes according to seasons. During the cold season, the precipitation covers the needs of the potential evapotranspiration and allows the formation of the RFU from where the vegetation appears. The two curves follow the same trend (**Figure 6**). The period from May to September correlates with the deficit period shown in the ombrothermal diagrams. The actual evapotranspiration (REE) is very low, as the lack of water available for the soil and plants due to drought is a limiting factor.

#### **3.4 Effect of climatic factors on evapotranspiration**

According to Emberger [42], the climate in the Mediterranean region is based on "the climatic characteristics which most strongly influence plant life". In the steppe region where water is a limiting factor, evaporation is very high and reaches its maximum in summer. The slice of water evaporated annually is almost always greater than the total amount of rain that has fallen [29].

In the study area, we found that the PET is significantly higher than the rainfall received. Thus, we consider that this period is a sequence of water deficit (drought) for spontaneous vegetation. To this end, the dominance of PET generates and/or promotes the process of soil degradation and more particularly the silting up of croplands and steppe rangelands [25].

#### *3.4.1 Effect of aridity*

The Naâma region corresponds to an arid area, more or less nuanced according to the orography, and the level of the relief and the capacity of the substrates to retain water from precipitation are low. According to Mjejra [17], in any region

marked by aridity, the potential evapotranspiration loss represents 60–80% of the rainfall input.
