The rhythm of life in Africa is not shaped by the temperatures, but by the precipitation or the rainy and dry seasons, because the amount and the seasonal distribution of precipitation are the decisive ecological factors for plant growth.
CLASSIFICATION OF REGIONS ACCORDING TO RAINFALL
Year-round precipitation is recorded only in the central Congo Basin, the region around the Niger estuary, eastern Madagascar and the coastal areas in the far west of the continent. With annual rainfall of more than 1000, often even more than 2000 millimeters, they are among the tropical regions with a humid climate all year round.
Precipitation is linked to the location of the Innertropical Convergence Zone (ITCZ), where the northeast and southeast trade winds converge and lead to convective clouds. Onshore equatorial westerly winds, the so-called Walker circulation, sometimes increase the precipitation.
These core areas of year-round precipitation are followed by an equatorial type of precipitation with a summer rainy season and a large winter dry season, which lasts a maximum of six months. The annual precipitation here clearly exceeds 800 millimeters.
The type of precipitation with two arid phases per year – a small dry season in summer and a large one in winter – characterizes the precipitation regime in the dry savanna regions of Africa.
The precipitation falls when the ITCZ passes in the direction of the tropics and when it retreats to the equator. If the advance of the ITCZ towards the tropics and its retreat, which was tied to the zenith of the sun with a certain delay, coincide closely in time, the two maximum precipitation levels in tropical Africa merge to form a summer rainy season (tropical summer humid type).
With annual precipitation amounts well below 800 millimeters, more than eight months of the year are usually arid. In the tropics there are fully arid deserts with annual rainfall of well below 250 millimeters.
REGIONAL CLIMATIC PHENOMENA
On the west coast of South Africa, the aridity on both sides of the tropic is increased by the neighborhood of the cool Benguela Current.
In Southeast Africa, on the other hand, a subtropical high pressure area over the southern Indian Ocean controls humid air masses almost all year round, which leads to considerable precipitation on the east coast of Madagascar (windward effects). In this region there is a summer humid east side climate typical of the subtropics, as it is also developed in East Asia.
The Maghreb region in the far north and the Cape region in the far south of Africa are influenced by the subtropical winter rainy climates.
East Africa has an exceptional position among the climatic regions of Africa. According to the latitude, its southern part would be assigned to the always humid inner tropics, its northern part to the alternately humid outer tropics. In fact, the Horn of Africa is occupied by semi-desert, the annual rainfall is only between about 100 and 500 millimeters per year.
Another arid region in East Africa is the Turkana Basin in northern Kenya, just north of the equator. Here the location in the lee of the Ethiopian highlands is one of the causes of the aridity, the leeward effects come into play during the northeast trade wind regime in the winter months. During the summer months from June to August, the highlands around the Turkana basin warm up very strongly. The associated convective ascent draws air masses in the form of valley winds from the Turkana Depression. These winds are compensated for by falling air movements over Lake Turkana, and clouds dissolve.
According to Countryaah.com, precipitation falls in the tropical arid regions of North Africa only during the rapid passage of the ITCZ in the transition seasons, concentrated on a few days a year.
THE CULTIVATION ZONES
The map is based on the largely parallel arrangement of the vegetation zones between the Sahara and the Lunda wave. A humid savannah belt follows the evergreen rainforest of the Congo Basin and the remnants of the monsoon forest of West Africa. A wide zone of dry and thorn bush savannahs adjoins it. Deserts and semi-deserts reach the size of a “continent” in the Sahara; in the Horn of Africa, in East and South Africa, parts of the coastal zone and inland areas are desert-like. The highlands of Ethiopia and the East African highlands show a vertical landscape structure in height levels.
The agro-ecological structure of Africa forms the framework for the distribution of the livestock industry. The wet savannahs and rainforests of the lowlands are contaminated by the tsetse fly, so that large-scale cattle farming is not possible; the dry savannahs, the highlands of the tropics and the semi-arid to humid subtropics are therefore the main areas of animal husbandry. The degree of market orientation in livestock farming varies greatly. Livestock is an important commodity today, be it sheep, dromedaries and donkeys in North Africa, cattle, goats, sheep and donkeys in the dry savannas, the subtropics and highlands, goats, pigs and poultry in the rainforest zone.
The zonal arrangement of the climatic areas and their elevation is reflected in the distribution of crops : In the food crops, cassava and plantain dominate in the rainforest zone, yams in the wet savannah, millet and peanuts in the dry and thorn savannahs. Rice cultivation on irrigation areas is playing an increasing role. Wheat cultivation has its main distribution in the subtropical winter rain areas, in the subtropical and tropical semi-deserts and deserts the date. In the highlands, corn, beans and sweet potatoes are staple foods. The crops marked by oblique hatching are cultivated on the one hand for personal consumption, but to a considerable extent also for the local and regional food markets.
Even with the mainly export-oriented crops, references to the eco-zones and altitude levels can be made: in the ever-humid tropics, oil palms are grown as plants that produce fat, cocoa trees and coffee bushes as luxury food plants, and Hevea brasiliensis as a tree that supplies rubber. The savannahs are the areas of origin of cotton and peanuts. In the higher areas, shrub cultures provide the valuable Arabica coffee and tea. As typical Mediterranean crops, citrus fruits and vines are grown in the far north and south of the continent.
To the north of the Sahel zone, dry areas determine the conditions for agriculture. There it is tied to local groundwater resources and the Nile (oasis farming). Agriculture without irrigation is only possible in individual areas north of the Atlas Mountains and on the Mediterranean Sea. Despite the narrow spatial boundaries of the cultivation areas, agriculture in this part of Africa is very productive and an important economic factor.
