Bio-climatic zones

 

by  Saley Bana Zakari ; Yamba Boubacar  and  Bouzou Moussa Ibrahim
Geography Department, FLSH, Abdou Moumouni University of Niamey
B.P. 418 Niamey, Niger, email : depgeo@ intnet.ne


Approach and data

The data source for this elaboration of the bio-climatic zones of Niger was exclusively the National Meteorological Service (DMN). Within the observation network the quality and length of data series vary considerably. In order to gain a better understanding of the spatial variability, only data from stations covering the period 1969-1998 were used, which corresponds to the most recent climatic situation.

With respect to its importance in tropical latitudes, rainfall is the best observed climatic parameter. Actually, 38 stations cover the required period (table 1). Besides rainfall, information about the minimal and maximal temperature and relative humidity was gathered. These parameters were available from 11 synoptic stations. In addition a station at Gaya offers data from 1970 onwards.
For the same stations the water balance was evaluated for the period from 1979 to 1998 based on the data of potential evapo-transpiration. Statistics were conducted with "Excel" software. The interpolation of rainfall isohyetes was done with the software "Surfer". The rainfall indexes differentiating the climatic zones were adopted from Charre (1974) and Morel (1982) as given in the following:

Annual rainfall > 750 mm Northern Sudan or “Dendi”
 > 450 < 750 mm Western and Central Sahel
 > 250 < 450 mm Northern and Eastern Sahel
 > 50   < 250 mm Arid or Desert Margins
 < 50 mm Hyper-arid or Desert

Monthly data on seasonal rainfall distribution was analysed for reference stations in each zone. Climate diagrams were developed on the approach of Gaussen and Bagnouls (P > 2T), allowing the determination of the length of dry and wet season. Additionally, the climatic water balance based on rainfall and potential evapo-transpiration was calculated for the same reference stations.
 

About the map
The map shows, that aridity is a permanent situation for at least 75 % of the territory. The difficult climatic situation is obvious from the negative climatic water balance for the whole country and the limited rainy season with the length decreasing towards the north of the country. The relative humidity is in general low with a maximum of 67 % and a minimum of 33 % in the south-east and between 44 and 13 %  at Bilma in the north. The rainfall is low, and moreover, unevenly distributed with regard to time and space. It is decreasing towards the north, with about 50 mm in the extreme desert and  about 750 mm in the south-west of the country. For the whole country the average temperature is in general elevated with low fluctuations.A clear latitudinal zonation is observed which determines the ecological zones and has also a strong impact on the socio-economics. Five different bio-climatic zones can be distinguished as given above, mainly based on the degree of aridity.

Northern Sudan (Dendi)
The Dendi is characterised by the weakest climatic constraints. The rainy season lasts four to five months with an average annual rainfall >700 mm. The annual climatic water balance shows a deficit of 1374 mm at Gaya, and the temperature amplitude reaches 8 °C. The vegetation has Sudan type character, developed on concretionary, illuviated ferruginous tropical soils, associated with less developed soils on gravel.

Western and Central Sahel
The rainy season here is restricted to three to four months with and average annual rainfall of 450 – 600 mm. At Niamey the annual climatic water balance reaches a deficit of 2165 mm with a temperature amplitude of about 10 °C. It is characterised by a transitional Sahelo-Sudanian vegetation type which is strongly influenced by human activities like firewood cutting or deforestation for agricultural use. More or less illuviated red sandy soils are widespread.

Northern and Eastern Sahel
The zone is marked by strong climatic constraints. Average annual rainfall reaches only values between 250 and 450 mm. The rainy season rarely exceeds three months. Especially at the northern boundary agricultural activities agricultural activities are at risk regarding an annual climatic water balance deficit of 2472 mm. Xerophile vegetation forming a prairie-like vegetation is dominant. Red-brown arid soils developed on dune sand are common.

The Arid Zone
The climatic characteristics are extreme to very extreme. With its low and erratic annual precipitation (50-250 mm) this zone is not suited for rain fed agriculture, except nomadic pastoralism.  The vegetation is typical sahelian and shows at the southern boundaries a prairie-like vegetation dominated by grasses which tends to contraction towards the north. Soils show only minor stages of development.

The Hyper-arid Zone
Extreme aridity is characteristic for this zone. The water balance is always negative; the annual temperature amplitude is elevated in relation to the mean value (whole Niger). Rainfall is erratic and an exceptional event with the exception of elevated mountain areas (i.e. Air). Vegetation is nearly absent. Only in oasis date palms are grown.
 

References

J. Charre (1974); Le climat du Niger, thèse de doctorat 3e cycle; Université     Joseph Fourrier; Grenoble, 188 p.

A. Morel (1980); Le climat du Niger; in Atlas Jeune Afrique, 64 pages.


Annotations
 

Table 1: Precipitation data used

Map 1

Climate diagrams:

1  Bilma

2  Agadez

3  Tahoua

4  Tillabery

5  Niamey

6  Gaya
 

Data Links

Download data of this project

Includes the following data (if available) compressed into one "zip" file:

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