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Climate

The climate is subtropical with summer rains from November to April, varying from 1200-1400 mm per year in the North-West to 650-750 mm per year in the South, a cold, dry winter season from May to August with occasional radiation frosts in depressions and a hot, dry season from September to October.
Temperatures vary from mean maxima of 28-30C. to mean minima of 12 -15C. Temperatures are considerably influenced by altitude and the mean maxima are seldom attained at the higher elevations. Temperatures are most equable on the plateaux, the coolest area being the ‘Tanganyika' plateau between Mporokoso and Mbala. The middle and South-West of Barotse Province has the greatest extremes with hot weather maxima of 110-l20F. but freezing locally in winter. The upper valleys are warmer than the plateaux but without extremes. The lower valleys are consistently hot, even during the rains. Relative humidities vary from 74-85 % in the rainy season of November to March to 50-60 % in winter—April to August—to 45 % in the hot season of September-October. The prevailing wind is easterly. Freak whirlwinds occur locally on occasions. Although Zambia lies within the subtropics the climate is tempered by altitude and compares favourably with climates of more temperate regions.

Geology

Guernsey (1952) has adequately summarised the geological features of the country. The general geologic framework of Zambia consists of an elevated basement of crystalline rocks to the east flanked on the west by successively younger sedimentary formations. The crystalline basement consists of two groups of sedimentary and volcanic rocks intimately associated with gneisses and eruptive rocks of granitic habit. 
Lying unconformably on the Older Granite and Basement groups and occupying nearly all the central and north-western parts of the country are four groups of sedimentary strata of varying age-(1) Katanga; (2) Kundelungu; (3) Karroo; and (4) Kalahari systems.
The oldest and most extensive is the Katanga system, the youngest the Kalahari system. The Karroo system contains the oldest known fossiliferous strata in the country. Karroo sandstones floor the rift valleys of Gwembe and Luangwa and most probably have a considerable development in the west where they are concealed by Kalahari sands. The Kalahari sands are probably the erosion product of the weak upper Karroo sandstone. The rocks of the Katanga, Kundelungu and Karroo systems are concealed to a considerable degree under residual, colluvial or alluvial soils or in areas of topographic relief under talus. Residual soils and alluvium are particularly noteworthy on the flatter parts of the plateau, colluvial and alluvial soils in the valleys.


Geomorphology

The present landscape began to be formed at the close of the Karroo period (Triassic). Following a long period of deposition of Karroo sediments warping occurred along a SW-NE axis which brought into being the Congo-Zambezi watershed (Kabwe to Isoka) along an upfold with the down-warped basins of the Congo and Zambezi on either side The Zambezi drainage was directed originally towards the Kalahari, but the disruption of Gondwanaland and the opening of the Mozambique channel initiated drainage towards the Indian Ocean. During Jurassic times an erosion surface of karroo sandstone was formed over most of the area. The remains of this peneplain in the west are blanketed by the Kalahari sands.

In the following Cretaceous period Zambia was subjected to a series of shock waves which caused upwarping along NW-SE axes. These were associated with the East African rift faulting. There were four such major axes:

  1. Upwarping of the Katanga pedicle blocked the Chambeshi River and caused the formation of the Bangweulu swamps.

  2. Upwarping between Feira and Chisamba diverted the Lunsemfwa River and the Luangwa River which previously joined the Zambezi River near the Kafue River junction.

  3. Upwarping west of Namwala blocked the Kafue River and caused the ponding of the Lukanga swamp and Kafue flats.

  4. Upwarping from Senanga to the Caprivi Strip blocked the Zambezi River causing the inundation of the upper Zambezi basin which still leaves an effect in the flooding of the Barotse plain.

At the same time rift faulting occurred along the middle Zambezi (Gwembe) and Luangwa valleys where the Karroo rocks were let down several thousand feet. This completed the diversion of all the Zambezi drainage from the Kalahari to the Indian Ocean. Following the upwarping and rift faulting, peneplanation took place during the late Cretaceous to form the Gondwana peneplain around 1,380 m. Only a few inselbergs remain of this erosion surface. This was followed by a further erosion cycle which, by the mid-Tertiary period, produced the Miocene peneplain around 1,230-1,290 m. This is the present main plateau area of Zambia. Further erosion during the late-Tertiary period produced a valley peneplain which is represented by the slopes to the major stream and river valleys.

Topography and soils

Plateau
The main plateau region stretches either side of the main Congo-Zambezi watershed from Kabwe to Isoka (part of the Continental divide), and represents the remnants of the once extensive Miocene peneplain surface. It is underlain by rocks of the Basement Complex (schists, gneisses and quartzites) and the Old Granite. The elevation rises from 1,230 m. at Kabwe to over 1,535 m. at Isoka. Two other extremely similar plateaux exist, the Southern Plateau around Choma-Kalomo, at just over 1,230 m., and the Eastern Plateau in Eastern Province, at about 1,075 m. These three plateau regions have very similar soils; they are shallow, slightly acid, structureless, fine textured, pale or pallid, poor in nutrients and humus, and frequently underlain by quartz rubble or concretionary ironstone (laterite) developed under conditions of peneplanation.

Upper Valley
This region lies mainly at an elevation of 920-1,075 m. The main extent is a belt surrounding the Kafue Flats on the North, East and South sides, extending to Mumbwa, Kabwe (just), Chisamba, Kafue, Mazabuka, Monze and Pemba. The topography is very flat, apart from some half-buried inselbergs from the previous Gondwana erosion cycle, and the incised valleys of a young drainage cycle. The soils are frequently red or red-brown clays and heavy sandy clays, sometimes containing an appreciable illite clay fraction. The soils become more pallid towards the Kafue Flats. They are slightly acid, but have a much higher base-exchange capacity than is found elsewhere except on soils derived from gabbro or basalt.

Lower Valley
These soils are a very heterogeneous collection, but occur in a well-defined physiographic region. They are found at elevations of 370-920 m. in the Luangwa, Lunsemfwa and Zambezi valleys, with scattered outliers in Barotse Province near the Zambezi River. The annual rainfall is from 500-750 mm. and the climate hot. These valleys are deep ancient troughs, underlain exclusively by Karroo strata, which are rare elsewhere in the country. The soils comprise brown mopane clays with lime-concretions, areas of brownish sands, and patches of fertile young alluvium near the major rivers. Some areas are covered by a continuous layer of water-worn pebbles and boulders. Some of the soils are residual Karroo soils, some are colluvial, derived from the escarpment bordering the valleys, and some are of alluvial origin. The lower areas of the valleys are subject to flooding in the rains, but the only perennial streams are those which enter from the plateau, and most of the Lower Valley soils are extremely dry in the dry season.

Lake Basin
The soils of the Lake Basin area (especially around Lake Bangweulu), in the Luapula and Northern Provinces are generally rather pale, yellow-brown to grey in colour. They are very acid (pH often less than 5.0), and typically have a deep humic staining, to depths of 0.3-1.0 m. The texture is variable, but usually rather sandy. They are poor in nutrients, frequently being particularly deficient in calcium, potassium and available nitrogen. As mentioned above, they probably represent old lacustrine alluvia; the ridge on which Samfya stands is an old lake sandbank. The deep humic layer testifies to conditions of poor aeration which persist to this day

Kalahari Basin
This basin, which is tilted gently southwards, dropping from 1,075 m. at Balovale to 950 m. at Sesheke and to 860 m. in South Africa, is rimmed in Zambia almost entirely by Karroo strata or recent alluvia. The geology within the basin is unknown in Zambia. In Botswana, it is largely underlain by Karroo beds. The basin is almost completely covered by sand of Kalahari type, with patches of grey, fine-silty alluvium on the Barotse plain and locally on other plains. The rainfall decreases steadily southward, from 1,375 mm. at Mwinilunga to 825 mm. at Mongu, and 700 mm. at Sesheke and Livingstone. The temperatures toward the southern end of this area are high, but radiation frosts are common in depressions in the cold season.

Source: D. B. Fanshawe, The vegetation of Zambia, 1971

Landscapes

The following landscapes occur in Zambia

  • Dambos
  • Flood plains
  • Hills and faulted scarps of the rift valley (variable slopes)
  • Hills and minor scarps (slopes predominantly over 16%)
  • Lake
  • Plains: sedimentary (Aggraded Plateau, Slopes 0-3%)
  • Plains: slightly dissected
  • Plateau: dissected (slopes 5-16%)
  • Plateau: flat to gently undulating (slopes 0-5%)
  • Rift valley: footslopes and dissected upper valleys (slopes 5-16%)
  • Rift valley: older alluvial plains and higher river terraces (slopes 0 - 3%)
  • Swamps

Source: UNZA - soil department

Dambo margin
Dambo margin

Kanyere Valley
Kanyere Valley

Limestone Namaila
Limestone Namaila

 Updated: 14 April 2014
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