*2.1.3.1 Bioclimatic study*

As part of our study, we took into consideration, as climatic parameters: rainfall and temperature because they represent the essential element of plant growth, soil

**Figure 3.** *Map of the main plant formations in the Naâma region [28].*

formation and evolution. Several studies were carried out about the climate of steppe regions in Algeria [29–36].

The study of the climate and bioclimate is based on the automated processing of old meteorological data [29], taken over 25 years (1913–1938) and from the recent period (1990–2014). All data are collected from the National Meteorological Office (NMO) [37].

• Presentation of weather stations

From a climatic point of view, the Naâma region inscribes its territorial limits on three distinct geographic natural domains:


Temperature and precipitation values are synthesized to determine climatic parameters for the entire study region by extrapolation. Data are listed in **Table 2**.

**Rainfall:** The geographical location of the study region shows decreasing rainfall gradient from North to South. The distribution of the average monthly rainfall during the periods 1913–1938 and 1990 to 2014 is presented as follows.

**Temperatures:** Temperatures are an important component of plant life, especially the two extremes: The lowest average temperatures are in January for the three stations, while the highest averages are in July for the three stations (**Table 3**) according to data from NMO (**Table 4**) [37].

Calculation of different climatic parameters

**De Martonne aridity index:** The aridity index is a quantitative indicator of the degree of water scarcity present in a given location. The De Martonne index is given by the formula below [38].

$$\mathbf{I} = \mathbf{R}/\mathbf{T} + \mathbf{10} \tag{1}$$

Where: R = Average annual rainfall in mm and T = Annual average temperature in °C. When the index is low, the climate is more arid, and vice versa (**Table 5**).

**Calculation of thermal continentality:** The thermal continentality is given by the Debrach method [39]. It is distinguish four types of climates:



**Table 1.**

*Main reference weather stations in the study region [36].*


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

> **Table 3.**

P2

(1990–2014)

 7,44

 9,12

 12,69

 15,95

 20,60

 25,84

 29,53

 28,53

 23,85

 18,24

 11,90

 8,29

*Monthly mean temperatures (°C) (from 1913 to 1938 and 1990–2014)*

 *[37].*

#### *Climate Change in Asia and Africa - Examining the Biophysical and Social Consequences…*


#### **Table 4.**

*Average values of temperatures and rainfall in the study stations.*


#### **Table 5.**

*De Martonne aridity index class [38].*


Where: M: average temperatures of the maximums of the hottest month. m: average minimum temperatures of the coldest month.

**Seasonal regime:** The seasonal regime presents the seasonal variation: the sum of the seasonal rainfall of Winter, Spring, Summer and Autumn. According to Despois [40], the study of the rainfall regime is more instructive than comparing annual averages or totals.

For this purpose, we calculated the amount of rainfall for all the study stations, during the four seasons.


**Climate summary:** Climate synthesis is based on the search for formulas that allow the action of several ecological factors to be reduced to a single variable. For this, several climatic indices, taking into account variables such as rainfall and temperatures, have been formulated for a synthetic expression of the regional climate.

We will retain the pluviometric quotient of Emberger [41, 42], which remains the most effective index in the description of the Mediterranean climate, the xerothermic index of Bagnouls and Gaussen [43] and thermal continentality and rain.

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

Several methods and indices have been used in the climatic classification of the Mediterranean region, including the method of Bagnouls and Gaussen [43, 44] and that of Emberger [42].

**Pluviothermal quotient:** Emberger [42] proposed a pluviothermal quotient, which tells us about the xeric character of the vegetation and which takes into account temperatures and rainfall. The latter exercises a preponderant action for the definition of the global drought of the climate. Emberger's quotient is specific to the Mediterranean climate. The quotient Q2 was calculated by the following formula [42]:

$$\mathbf{Q}\_2 = \left[ 2000 \mathbf{R} / \mathbf{M}^2 - \mathbf{m}^2 \right] \tag{2}$$

Where: Q2: the pluvio-thermal quotient, R: Average annual rainfall in (mm), M: the average of the thermal maxima of the hottest month in Kelvin, m: the average of the thermal maxima of the coldest month in Kelvin. The Q2 allowed us to locate our weather stations on the Emberger climagram.

**Bagnouls and Gaussen temperature diagram:** The ombrothermal diagrams of Bagnouls and Gaussen make it possible to compare the evolution of the values of temperatures and precipitations. On this subject, Emberger specifies: "a climate can be meteorologically Mediterranean, possessing the characteristic Mediterranean pluviometric curve, without being so ecologically or biologically, if the summer drought is not accentuated".

The study region is characterized by minimum temperatures between: - 0.3 and 2.12° C. Le Houérou *et al.* [45] consider that the Algerian steppes are surrounded by isotherms "m" - 2 and 6° C, and that M-m varies little and remains approximately equal to 32.6–37.9° C. These temperatures explain the absence of certain species whose life is linked to temperate winters.

#### *2.1.3.2 Methods for estimating evapotranspiration*

As part of this work, evapotranspiration is calculated for the three meteorological stations in the Naâma region using the Thornthwaite method.

The Thornthwaite Method is an empirical formula for estimating potential evapotranspiration, relatively simple to implement, since it requires few data (average air temperatures, in particular). One of the drawbacks of the Thornthwaite method is its monthly time step for calculating potential evapotranspiration.

Calculation of PET is done by applying Thornthwaite's formula; it is a simple expression suitable for arid climate. This Thornthwaite Method is one of the most widely used formulas for the calculation of evapotranspiration is that of Thornthwaite [46].

It has been tested in several regions of Algeria and in the Mediterranean because it gives acceptable results.

By statistically fitting the results of experimental measurements of the PET to climatological data, Thornthwaite established a non-linear relationship between the mean monthly PET and the monthly mean temperature (Tm) expressed like this:

**Potential evapotranspiration:** it is the consumption of water, under the combined action of the evaporation of water from the soil and the transpiration of the plant. For its estimation, methods based on climatic variables are used. However, the choice depends mainly on the type of climate data available and the type of climate in the region. However, ETP data for the three stations (Mécheria; Naâma, Ain Sefra) are estimated using the Thornthwaite method [46].

$$\text{ETP} = \mathbf{16} (\mathbf{10} \times \mathbf{T} / \mathbf{I})^\mathbf{a} \text{ K} \tag{3}$$

Where PET: is the monthly potential evapotranspiration, expressed in mm T: the monthly average temperature of the month considered in degrees Celcius.

a: Coefficient given by the expression: a = 1.6 (I/100)+0.5.

where the annual thermal index I is equal to the sum of the twelve values of the monthly thermal index: i = (T/5) 1.514 K: Correction coefficient, which depends on the latitude i: monthly thermal index I: Annual thermal index.

$$I = \sum\_{m=1}^{12} i(m)\,i(m) = \left[\frac{\overline{\mathbf{T}}(m)}{\mathbf{5}}\right]^{1.514} \tag{4}$$

**Real evapotranspiration (RET) or flow deficit:** This is the quality of water that is actually evaporated or transpired by the soil, plants and free surfaces. The RET can be estimated by several methods; for our case we have chosen the Turkish formula [47]:

$$ETR = \frac{P}{\sqrt{\mathbf{0.9} + \left(\frac{P}{L}\right)^2}}\tag{5}$$

Where: P: designates precipitation in mm.

L: designates a constant dependent on the temperature with L = 300 + 25 T + 0.05 T<sup>3</sup> andT: is the annual average temperature in °C.

The water balance by the Thornthwaite method

Its purpose is to quantify the water transfers resulting from precipitation, and to characterize a soil from a dryness or humidity point of view.

According to Thornthwaite, the water quality needed for a soil to be saturated is equivalent to a 100 mm depth of water, (this is the generally accepted useful reserve). Still according to Thornthwaite, one can establish a monthly hydrological balance during the period (1990–2014), which makes it possible to estimate for each month: the real evapotranspiration (RET).

### **3. Results and discussion**

#### **3.1 Climate analysis**

#### *3.1.1 Rainfall*

The climate of the Naâma region is Mediterranean; is characterized by a rainy winter and dry summer. The average annual rainfall for the period from 1990 to 2014 is 243.11 mm in Mécheria. It is 218.75 mm in Naâma, and 199.64 mm in Ain Sefra. The months of July are the driest (5.28 mm for Mécheria 5.64 mm in Naâma and 4.72 mm for Ain Sefra); October is the wettest month (35.79 mm for Ain Sefra, 31.32 mm Naâma and 35.52 mm for Mécheria). The monthly breakdown shows that July and August are the two driest months (5.28 mm for Mécheria, 4.72 mm for Aïn Sefra). On the other hand, the same findings (5 mm for Mécheria, 7 mm for Aïn Sefra, 2 mm Naâma) were recorded for the recent period. On the other hand, the months of October and November are the wettest in the two old and recent periods (43 mm for Mécheria, from 29 to 35.79 mm for Aïn Sefra). The comparison between the rainfall series (1913–1938 and 1990–2014) highlights the nature of the decrease or increase in significant rainfall which is a phenomenon of almost general climatic
