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Course Information

• Institution: Kwame Nkrumah University of Science & Technology, Kumasi, Ghana
• Course Code: NRFS 151
• Course Title: Meteorology & Climate Change
• Credit Hours: 3
• Programs:
  • B.Sc. Natural Resources Management
  • B.Sc. Aquaculture & Water Resources Management
• Instructor: Dr. Thomas Kwaku Agyemang
• Department: Department of Fisheries & Watershed Management
• Faculty: Faculty of Renewable Natural Resources
• College: College of Agriculture & Natural Resources
• Lecture No.: 8

Learning Goals

• By the end of this session, you will be able to:
  • Define climate and climatic zones.
  • Explain the factors controlling climatic zones.
  • Identify the major global climatic zones.
  • Describe the climatic zones of West Africa.
  • Explain the climatic zones of Ghana and their characteristics.
  • Discuss the importance of climatic zones for water resources, agriculture, and ecosystems.

Key Concepts

Climate and Weather

• Climate: Refers to the long-term average pattern of weather conditions in a region, typically measured over 30 years or more. Climate includes averages of:
  • Temperature
  • Rainfall
  • Humidity
  • Wind
  • Atmospheric pressure
• Weather: Represents short-term atmospheric conditions.

Climatic Zones

• Definition: Climatic zones are large geographic areas characterized by similar climatic characteristics, including:
  • Temperature patterns
  • Rainfall distribution
  • Seasonal variations
  • Vegetation types
• Broad Definition: Climatic zones are defined by distinct long-term weather patterns, primarily classified based on:
  • Temperature (insolation)
  • Precipitation (amount, seasonality, and intensity)

Factors Controlling Climatic Zones

1. Latitude

   • Determines solar energy (insolation) received by an area.
   • Areas near the equator receive more direct sunlight, leading to hot climates.
   • Higher latitudes receive less solar energy, resulting in cooler climates.
   • Example: West Africa lies between 4°N and 11°N, hence tropical conditions with rainfall-driven temperature variation.

2. Altitude (Relief/Topography)

   • Temperature decreases with height at a rate of approximately 6.5°C per 1000 m.
   • Mountains can create orographic rainfall patterns, influencing local climates.
   • Example: The Mampong-Ashanti highlands have slightly lower temperatures and higher rainfall than surrounding lowlands.

3. Ocean Currents

   • Act as conveyor belts for warm or cold water, affecting coastal climates.
   • Warm currents increase temperature and humidity (e.g., the Guinea Current).
   • Cold currents can lead to dry conditions and coastal fog (e.g., the Benguela Current).

4. Distribution of Land and Water (Continentality)

   • Land heats and cools faster than water.
   • Maritime climates (coastal areas) have moderated temperatures due to the ocean's heat sink effect.
   • Continental climates (inland areas) experience extreme temperature fluctuations.
   • Example: The Gulf of Guinea moderates temperatures along the south coast of Ghana, while northern zones see higher temperatures and cooler nights.

5. Prevailing Winds

   • Global wind systems redistribute heat and moisture, affecting local climates.
   • Winds from oceans tend to bring moisture and rainfall, while dry continental winds bring aridity.
   • In West Africa:
     • Southwest Monsoon winds bring rainfall.
     • Northeast Trade winds (Harmattan) cause dry conditions.

6. Vegetation Cover

   • Vegetation influences climate through mechanisms such as evapotranspiration, affecting local humidity and temperature.
   • Dense forests create cooler, wetter microclimates.
   • Sparse vegetation leads to hotter, drier conditions.

Köppen-Geiger Climate Classification System

• This system categorizes global climates into five primary types based on temperature and precipitation, with a sixth category for highlands (H).
• Major climate classifications include:
  1. Tropical Climate (A)
  2. Dry/Arid Climate (B)
  3. Temperate Climate (C)
  4. Continental Climate (D)
  5. Polar Climate (E)
  6. Highland Climate (H)
• The classification considers seasonal patterns such as summer heat or winter droughts.

Subdivision Criteria for Climate Zones

• Climate zone letters may be followed by additional letters to indicate specific conditions:
  • f: No dry season (humid).
  • m: Monsoon climate.
  • w: Dry season in winter.
  • s: Dry season in summer.
  • h: Hot summer (annual temperature).
  • k: Cold summer (annual temperature).
  • a: Hot summer.
  • b: Cool summer.

Detailed Climatic Zones Characteristics

A: Tropical / Megathermal Climates (Warm & Wet)

• Characteristics:
  • High temperatures throughout the year (>18°C).
  • Heavy rainfall with no winter season.
  • High humidity and little seasonal temperature variation.
• Common Vegetation:
  • Tropical Rainforest (Af)
  • Monsoon (Am)
  • Savanna (Aw/As)
• Locations:
  • West Africa, Central Africa, Amazon Basin, Southeast Asia.

B: Dry (Arid and Semiarid) Climates

• Characteristics:
  • Low rainfall with high evaporation rates.
  • Evaporation exceeds precipitation.
  • Sparse vegetation types.
• Types:
  • Arid climates: Hot Desert (BWh), Cold Desert (BWk).
  • Semi-arid climates: Hot Steppe (BSh), Cold Steppe (BSk).
• Example: Sahel region in West Africa.

C: Temperate / Mesothermal Climates (Mild)

• Characteristics:
  • Moderate temperatures with distinct seasons.
  • Moderate rainfall, mild winters, and warm/hot summers.
• Regions:
  • Europe, North America, East Asia.
• Examples:
  • Humid Subtropical (Cfa/Cwa)
  • Marine West Coast (Cfb/Cfc)
  • Mediterranean (Csa/Csb).

D: Continental/Microthermal Climates (Severe Winter)

• Characteristics:
  • Hot summers and cold winters with a large temperature range.
  • Moderate rainfall, often peaking in summer.
  • Distinct seasonal variations.
• Common Regions:
  • Europe, North America, Asia.
• Vegetation:
  • Dominated by grasslands (steppe), deciduous forests, and mixed forests.

E: Polar Climates (Very Cold)

• Characteristics:
  • Extremely cold temperatures with low precipitation.
  • Long winters and short cool summers.
• Common Regions:
  • Antarctica, Arctic regions.
• Examples:
  • Tundra (ET)
  • Ice Cap (EF).

West Africa Climatic Zones

• In West Africa, climatic zones are defined by a latitudinal gradient.
• Moving from the Gulf of Guinea north towards the Sahara, climate becomes drier with increased temperature range driven by the seasonal migration of the Inter-Tropical Convergence Zone (ITCZ).
  • ITCZ Definition: A belt of low pressure circling the Earth near the equator, formed by the convergence of the Northeast Trade Winds (Harmattan) and Southeast Trade Winds (Monsoon).
  • ITCZ Migration:
    • Migrates north and south with the sun, influencing wet and dry seasons:
    • Northward (March - October): Wet season (Monsoon).
    • Southward (November - February): Dry season (Harmattan).

Major Climatic Zones in West Africa

• Four Major Latitudinal Belts based on rainfall amount and length of the growing season:
  1. Guinea Coast / Equatorial Zone
  • Rainfall: >1,500 mm/year, characterized by bimodal rainfall.
  • Vegetation: Rainforest, high humidity, and little temperature variation.
  1. Guinea / Forest-Savanna Zone
  • Rainfall: 1,000 - 1,500 mm/year, also bimodal, acting as a transitional zone.
  • Vegetation: Mixed forest and savanna species.
  1. Savanna (Sudan) Zone
  • Rainfall: 900 - 1,200 mm/year, with a unimodal rainfall pattern.
  • Vegetation: Woodland/grassland with short grasses and thorny trees.
  1. Sahel Zone
  • Rainfall: 250 - 800 mm/year, with highly erratic unimodal rainfall.
  • Vegetation: Drought-resistant shrubs and grasses.

Ghana's Climatic Regions

Four Main Climatic Regions in Ghana

1. South-Western Equatorial Climate

   • Location: Western Region south of about 7°N (e.g., Takoradi, parts of Western North).
   • Climate Characteristics:
     • Bimodal rainfall pattern with >1,500 mm/year.
     • Temperatures: High humidity, little annual variation (24°C - 29°C).
   • Relevance: Significant for high biodiversity; risk of soil erosion.

2. Wet Semi-Equatorial

   • Location: Ashanti, Eastern, Bono Regions (e.g., Kumasi, Koforidua).
   • Climate Characteristics:
     • Transitional rainfall pattern (1,200 - 1,500 mm/year).
     • Moderate humidity with a comfortable climate.
   • Relevance: Essential for major cocoa production; supports freshwater aquaculture.

3. Coastal Savannah Zone

   • Location: Coastal plains from Tema to Aflao (e.g., Accra, Tema).
   • Climate Characteristics:
     • Bimodal, but low and erratic rainfall (600 - 800 mm/year).
     • High diurnal range with the highest mean temperatures in Ghana.
   • Relevance: Environmentally fragile, high risk of bushfires.

4. Northern Savannah (Guinea) Zone

   • Location: Northern regions including Tamale, Bolgatanga.
   • Climate Characteristics:
     • Unimodal rainfall pattern (900 - 1,200 mm/year) extends from May to October.
     • Long, harsh dry season dominated by the Harmattan.
   • Relevance: High water stress, emphasizing the need for irrigation strategies.

Summary of Implications for Water Resources

Concluding Summary

• The ITCZ is the primary driver of climate in West Africa and Ghana, resulting in four distinct climatic zones:
  • South-West Equatorial
  • Coastal Savannah
  • Wet Semi-Equatorial
  • Northern Savannah
• Rainfall seasonality is crucial for management strategies, particularly for agriculture and water resources.
• Knowledge of climatic zones is vital for sustainable practices in natural resource management, aquaculture, and planning for water infrastructure.

Group Discussion Questions

1. For Natural Resource Managers: What tree species characteristics are necessary for reforesting a degraded site in the Coastal Savannah?
2. For Aquaculturists: Which climatic zone would you choose for a commercial tilapia farm, and what adaptations would be needed for the Northern Savannah?
3. For Water Resources Managers: What specific design considerations are critical for a reservoir in the Northern Savannah compared to one in the Forest Zone?
4. General: Discuss the effects of diurnal temperature variations in ponds in different regions (Kumasi vs. Bolgatanga).
5. Water Resource Effects: Analyze how the Harmattan influences evaporation rates in the Bui Dam reservoir.
6. Climate and Fire Season: Explore how climatic zones affect the fire season in transitioning regions of the Bono region.