*3.1.2 Seasonal regime*

In general, precipitation is unevenly distributed during the seasons, as shown in **Table 6**. The most important precipitations are those which fall in autumn and spring, compared to that of winter, although that the latter constitute a significant contribution (**Table 6**). The table below shows the calculated seasonal regime of stations in the study region for the two periods.


#### **Table 6.**

*Seasonal rainfall patterns of the old period.*

The analysis of the climatic variability of rainfall totals is due to the spatiotemporal seasonal and annual variability of rainfall; this indicates a change in the climate of the study region (**Table 6**). In general, the rainfall is slightly different, where the autumn maximum is constant; some variations show transformations in the seasonal distribution of rainfall. Dominant autumn rains prevail over most of the study area, but the seasonal pattern may be locally modified slightly. The most remarkable fact is that the raising of altitudes characteristically resuscitates the arid climate. The dominant autumn rains prevail over most of the study region, but the seasonal pattern may locally undergo slight modifications between the 2 periods. This variation in seasonal regimes is explained by its essentially orographic character. The most remarkable fact is that the raising of altitudes characteristically resuscitates the arid climate. From south to north/east the formula becomes: AHAE / AHPE /HPAE/AEHP for the old period (1913–1938).

On the other hand, in the recent period (1990–2014), the most remarkable is the consistency of the APHE-type regime for the majority of the study stations. This transition to the dominant autumn rains is indicative of an accentuation of the oceanic character of the climate. This indicates that the rainfall has therefore increased during the cold season, and summer tends to become the dry period. Consequently, the current seasonal regimes (P2) are markedly changed this is explained by their "degree of continentality".

The distribution of precipitation appears in the study region as an essentially orographic phenomenon: the isohyets reflect the relief. The Tellian and Saharan Atlas plays a much clearer role as a barrier between maritime and continental influences. A succinct explanation of the rains is needed to understand the seasonal variations. In this area the rainy season lasts from 4 to 6 months with some rare local variations, the orientation of the winds appears essential.

Thus, over the past 25 years, the entire study region has been subject to the autumn or winter maximum. The autumn rainy season is prolonged there until December and even January. Here the influence of the relief regenerating the oceanic rain regime is evident. The rainfall figure rises with greater intensity during the winter season: it is therefore a question of relief precipitation. Overall, the evolution of annual precipitation and rainy seasons shows a very moderate decreasing trend between the 2 periods and the following ones, in agreement with observations made at the regional scale. These changes have had repercussions on the vegetation that occurs during the seasonal course of precipitation. The low rainfall is a characteristic of the Saharan climate. However, this region is poorly watered; rainfall is scarce and irregular, often brief (showers), but of high intensity, causing violent floods. The study of seasonal variability is essential, to see if the decrease or increase in rainfall is specific to a particular season or to several seasons, it allows to better visualize the chronology of the seasonal rainfall totals over time. The analysis of monthly average rainfall data makes it possible to better visualize the distribution of the quantities of water recorded at each station and for each month of the year.

#### *3.1.3 Temperatures*

Temperatures are an important element for plant life, especially the two extremes: the average of the coldest month's lows and the hottest month's average lows.

Temperatures represent an important element for plant life, especially the two extremes: the average of the minimums of the coldest month and the average of the maximums of the hottest month. We notice a significant increase in maximum temperatures between the two periods; therefore the series of maxima experiences a clear increase which affects all the months of the year, this situation is reflected at

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

the monthly level where the rise in temperatures fluctuates between 0.3°C to 1.5°C inducing to the annual scale an average increase of 0.5° C. This indicates a more marked global warming of the study region. This change in temperature is manifested by consequences on the metabolism and development of fauna and flora, growth, respiration, the composition of plant tissues and the mechanisms of photosynthesis (**Table 7**).

The highest temperatures are generally recorded in July for the three reference stations. The analysis of the maxima highlights the notion of climatic aridity which tends to strengthen from north to south of the region (**Table 7**). The period of high temperatures, lasting from June to October, can cause scalding due to increased sweating. Therefore, the hottest month of the year for the two thermal series (1913– 1938 and 1990–2014) is that of July and August with an average temperature of 29.9° C. (Mécheria) at 36.48° C (Naâma). The analysis of the maxima emerges the notion of climatic aridity which tends to strengthen from north to south of the region, so the average thermal amplitude between the southern and northern zones of the region reaches approximately 0.84° C. This value relative to the spatial extent (in the North–South direction) of the region is relatively high. For the period of low temperatures, from November to February, are at the origin of the intensity of winter frosts which can result in vegetative damage such as necrosis. So the coldest and most severe month is that of January for all the stations during the two thermal study series. On the other hand, the minimum series is experiencing a sharp increase affecting all months of the year with the exception of August. This situation is reflected at the monthly level where the rise in temperatures fluctuates between 0.3° C to 1.5° C inducing on an annual scale an average increase of 0.5° C.

### *3.1.4 Wind*

In the arid region, winds have played and still play a major role in the degradation of vegetation and soil destruction and the building of constrained dune systems; they constitute a permanent threat to biodiversity and infrastructure. Therefore, the wind can reach considerable speeds allowing it to exert erosive actions on the ground by the drying out of the superficial parts of the ground.

#### **3.2 Calculation of the different climatic parameters**

#### *3.2.1 Bioclimatic indices*

#### *3.2.1.1 De Martonne's aridity index*

The **Table 8** below shows the average annual temperature, the average annual precipitation and the aridity index calculated for the stations during the two periods.


**Table 7.**

*Thermal differences between P1 (1913–1938) and P2 (1990–2014).*


#### **Table 8.**

*De Martonne's aridity index.*

The comparative analysis of the De-Martone aridity index between the two periods allows us to advance that the study region is strongly marked by increasing aridity which is accentuated from North to South. This is due to the drought induced by the decrease in rainfall and the increase in minimum and maximum temperatures (case of 2001 when the recorded rainfall was 60 mm in Aïn Sefra … ). The values of the aridity index obtained are respectively 8 and 11 depending on the geographical position of the study stations. In the steppe space, for the stations of Mécheria and Naâma are characterized by a semi-arid to steppe climate. In the stations which are in the central part of the region, the Saharan Atlas (Aïn Sefra) the index is 7.53 and reflects a desert-like climate.

#### *3.2.1.2 Thermal continentality*

A comparative analysis of the two series (1913–1938) and (1990–2014) recorded at station level (**Table 9**), shows us that the region experiences a contrasting thermal regime, of a continental type. Indeed, the annual thermal amplitude of average temperatures is 30° C to 40° C depending on the North–South orographic gradient. The average seasonal difference can reach more than 30°C, thus promoting soil degradation by the relaxation of friable rocks in terms of erosion in the forms of wind and water erosion.

## *3.2.2 Climate synthesis*
