Topic 3: Africa: Climate and Vegetation Character of African Climate -Temperature -Precipitation & Evaporation -Implications Accounting for Climatic Differences -Atmospheric Pressure and Wind Systems in January (winter) in July (Summer) Topic 3: Africa: Climate and Vegetation Climatic Regions of Africa -Tropical Rainforest Climate (Af) -Savanna Climate (Aw) -Hot Steppe Climate (Bsh) -Cool Steppe Climate (Bsk) -Hot Desert Climate (Bwh) -Cool Desert Climate (Bwk) -Mediterranean Climate Topic 3: Africa: Climate & Vegetation Drought in Africa -Types of drought: meteorological drought agricultural drought hydrological drought -Patterns of Drought Distribution -Causes and Effects of Drought Topic 3: Africa: Climate & Vegetation Vegetation and Soils -Types and Patterns -Deforestation of Tropical Rainforest: Patterns Causes and Effects African Climate: Temperature most tropical continent by location, hence much of Africa has tropical climate however, the extreme northern and southern portions of the continent have subtropical climate temperature is high everywhere (>10 o C) spatial variation of temperature is gradual due to the absence of major relief features African Climate: Temperature (July) Map African Climate: Temperature (January) Map African Climate: Temperature however, prevailing high temperatures moderated in areas of high elevation pattern of temperature distribution is determined by: -local topography or elevation - offshore ocean currents -pattern of atmospheric circulation -land area African Climate: Temperature local topography or elevation: -hence much of East Africa is cooler offshore ocean currents: -cool currents depress local temperature, hence: Morocco Cape Verde Cape Town Cape Lopez, have cooler temperatures African Climate: Temperature pattern of atmospheric circulation: -lower winter temperature for northernmost and southernmost parts of Africa due to mid-latitude depression or westerly winds -example: Cape Town (13 o C in July (winter season) Algiers (12 o C in Jan (winter season) Land area -Southern Africa has smaller land area, hence comes under stronger oceanic influence and records lower temperature African Climate: Temperature distance from the coast: -temperature range increases away from the coast African Climate: Precipitation rainfall varies much more widely in amount and seasonal incidence than temperature hence, rainfall is a more critical variable for climate differentiation over much of Africa Generally, rainfall is highest within latitude 15 o north and south of the equator and decreases both northward and southward of the equator African Climate: Precipitation Map African Climate: Precipitation Rainfall is generally high: - along the coast of West Africa stretching into the Congo basin -northern Malagasy Republic (300 mm) -northern coast of Mozambique across to Angola African Climate: Precipitation However, anomalously low rainfall amount is observed along the coast of Ghana particularly east of Cape Three Points because of: -the tendency for winds to blow parallel to the shoreline so that frictional divergence occurs -and the relative coolness of its ocean water due to upwelling of cold water which has the effect of stabilizing the air and causing fog off the coast rather than precipitation African Climate: Precipitation rainfall amount is elevated in areas of high relief: -East African Highlands -mountains of southern Africa -hilly areas of Futa Djallon Mt., Cameroon Mt. and Jos Plateau Most parts of Africa receive their rainfall during the summer season, exception the coast lands of North Africa and Cape Town with winter rainfall African Climate: Precipitation Length of the rainy season increases towards the Equator rainfall regime is generally double-peak around the equatorial belt and becomes single peak regime the farther away from equator Rainfall amount, duration and regime are primarily controlled by the location and movement of the ITCZ Double-Peak Rainfall Regime Rainfall Regime and Movement of ITCZ A: Dry, HazeB: Moist Air Little Rain C:Deeper, Moist Air Convection, Line Squall D:Less intense more continuous rain Single-Peak Rainfall Regime African Climate: Precipitation Perpetually dry areas: -Sahara desert -Namibian desert and horn of Africa Sahara aridity caused by the permanent existence of high pressure (air subsidence) in the region Namibian coast land aridity caused by the effect of the cold Benguela current and the southeasterly that arrive as dry winds African Climate: Evaporation In general, evaporation increases away from the wet equatorial region to the dry savanna annual evaporation rate: -In humid equatorial regions is 2000 mm mean annual values of potential evapotranspiration (PE): ->114 cm in Africa north of the equator, except north Africa cool coast lands African Climate: Evaporation ->175cm recorded in the hinterland of West Africa, Sudan and Somali coast lands -400 mm of rain recorded in August alone in Kano City resulting in large dam (Bakolori dam disaster) failure Sahelian drought of first drew world attention to Africa drought problems since then, drought of greater intensity occurred in West Africa Sahel, Ethiopia, the Horn of Africa, East Africa and southern Africa Drought Affected Countries in Africa Drought in Africa MAIN TYPES OF DROUGHT: meteorological drought agricultural drought hydrological drought Drought in Africa Meteorological Drought: occurs when the amount of rainfall is less than the expected long-term average annual rainfall in the location or when percentage reduction or negative departure from the long-term average rainfall occurs Drought in Africa Meteorological drought definition has a number of problems: -paucity of data -does not account for soil moisture, ambient temperature, rates of evaporation, etc, important to policy makers and farmers -difficult to identify with any degree of reliability Drought in Africa Agricultural Drought: occurs when there is not enough moisture available at the right time for the growth and maturation of crops timing of precipitation throughout the growing season is as important as the absolute amount per month or season because crops have varying needs for moisture as they develop Drought in Africa occurs even when rainfall amount seems more than adequate and soil in valley bottoms and flood plains become waterlogged leading to diminished aeration and crop failure Drought in Africa Hydrological Drought: occurs when stream flow falls below a pre- determined level significant to hinder certain human activities like: -shipping -HEP generation -irrigation water distribution periods of low level of stream flow and extended period of soil dryness Drought in Africa Effects of Drought: scarcity of water for human and animal consumption widespread crop failure as soil moisture dries up widespread famine, hunger, malnutrition over 100,000 lives lost to famine in 1973 alone in the sahelian drought of 1973 Drought in Africa thousands of lives lost in 1983/84 in the sahel and in 1987 in the horn of Africa large-scale out-migrations of people from the sahel belt more than 10% of the population of Chad, Mauritania, Ethiopia, Niger became drought refugees slump in agricultural export and food crops Drought in Africa weak economies of drought affected countries intensification of desertification and increased dust storms and shifting sand dunes drastic reduction in lake levels and areal extent due to excessive loss of water: -in 1966, Lake Chad was 22,000 km 2 but dropped to