Module 4: Introduction to South Africa's Weather and Climate

Equatorial Regions in Africa

• Located near the equator, primarily in central Africa and the southern coast of West Africa
• Temperature characteristics:
• Hot temperatures prevail throughout the year
• Average temperatures range between 25°C and 27°C
• Limited temperature variation, with only a 3°C annual range
• Humidity and rainfall:
• Equatorial areas are highly humid
• Experience over 1,500 millimeters of rainfall annually
• Afternoon convection storms are the most common form of precipitation

Tropical Regions Around the Equator

• Encircle the equator, with major locations in East Africa, the Congo, and parts of the Sub-Saharan belt
• Adiabatic cooling:
• Rising air becomes cool
• Heat energy is used as the air expands, and pressure decreases
• Adiabatic cooling: process where rising air cools at 1°C for every 100 meters of ascent
• Dry Adiabatic Lapse Rate: the term for the rate at which rising air cools
• Effect on water vapor:
• Cooling air can hold less water vapor
• Condensation may occur as a result
• Cloud formation and rainfall may follow the condensation process

Effects of Subsidence and Convergence on African Rainfall

• Convection currents at the ITCZ:
• Strong convection currents near the equator create areas of low pressure
• Tropical Easterlies and convergence:
  • Strong winds from the north and south converge on the equatorial low-pressure belt
  • These converging winds are known as tropical easterlies
• Intertropical Convergence Zone (ITCZ):
  • The convergence zone formed by tropical easterlies is called the Intertropical Convergence Zone or ITCZ
• Effect on air and rainfall:
  • Hot air from the equator rises due to temperature
  • Convergence of tropical easterlies at the ITCZ causes air to rise, cool, and condensate
  • This process in equatorial regions leads to rainfall

High-Pressure Belts Between 15° and 30° Latitude

• Subsiding Air and High-Pressure Belts:
• Subsiding air creates high-pressure areas between 15° and 30° latitude
• These high-pressure areas are known as subtropical high-pressure belts
• Condensation and dry conditions:
• Condensation does not occur in the descending, warming air
• This lack of condensation results in dry conditions between the latitude points
• Impact on Sahara Desert:
• The subsiding air in this region contributes to the creation and persistence of the Sahara Desert in North Africa

Convergence at the Polar Front

• Air Mass Convergence and Polar Front:
• Air masses converging at the polar front lead to the rising of air
• Mid-Latitude Cyclones and Westerly Winds:
• Mid-latitude cyclones form due to the rising air and are carried by the westerly winds
• Formation of Cold Fronts:
• Cold fronts are caused by these mid-latitude cyclones
• Cyclonic Rain in Western Cape and North Africa:
• The Western Cape in South Africa experiences cyclonic (or frontal) rain during winter
• Similar conditions occur between 30° and 40° N in North Africa

Ocean's Impact on African Temperature

• Wind-Driven Ocean Currents:
• Winds continually blowing over the ocean surface create a dragging action, leading to the formation of ocean currents
• Warm and Cold Air Above Ocean Currents:
• Air above a warm ocean current is warm, while air above a cold ocean current is cold
• Influence on Coastlines:
• Prevailing winds carry warm and cold air from their respective ocean currents toward the land
• Ocean currents influence the coastlines they flow past
• Example in South Africa:
• In South Africa, the warm Agulhas Current flows down past the east coast, while the cold Benguela Current flows up the west coast

Ocean's Impact on African Rainfall

• Evaporation from Ocean as Main Precipitation Source:
• The primary source of precipitation over Earth's landmasses is the evaporation of water from the ocean
• Onshore Winds and Moisture Transport:
• Onshore winds from the sea to the land carry moisture to coastal areas, making inland places generally drier
• Effect of Warm Ocean Currents:
• Warm ocean currents lead to warmer air above them, capable of holding more water vapor, resulting in more rain in warm ocean maritime climates
• Effect of Cold Ocean Currents:
• Cold ocean currents, with colder air above them, hold less water vapor, causing less rain in colder maritime climates
• Examples from South Africa:
• The Kalahari Desert is influenced by the cold Benguela climate, leading to limited moisture and the formation of mist or fog
• The Namib Desert's existence is attributed to the cold Benguela Current
• The east coast of South Africa and Mozambique receives more rain due to the warm Agulhas Current

Explore the diverse climate regions of Africa and understand the key characteristics of each region. Learn how to locate Africa's climate regions and their unique weather conditions and patterns.