The Nigerian Climate – SS1 Geography Lesson Note (Second Term)

Climate is the average weather condition of the atmosphere over a long period of about 30 to 35 years.

Behavioural objectives

By the end of the lesson, students should be able to:

• define climate;
• list the factors that affect climate and the elements of climate;
• describe the characteristics of temperature in Nigeria;
• name the four types of wind in Nigeria and state their effects;
• describe the distribution of rainfall, insolation and relative humidity in Nigeria.

What are the factors affecting climate?

1. Latitude
2. Altitude
3. Distance from the sea
4. Ocean currents, etc.

What are the elements of climate?

1. Temperature
2. Rainfall
3. Wind
4. Relative humidity
5. Pressure
6. Cloud cover
7. Sunshine

How do the elements of climate behave in Nigeria?

Temperature

Temperature is the degree of hotness and coldness of a place. Temperature in Nigeria is not uniform and has the following characteristics:

1. It varies from place to place. Temperature is low in the south, with an average of about 24°C, because of the cooling effect of the Atlantic Ocean. It is high in the north because of the effect of the Sahara Desert or distance from the sea.
2. It varies with altitude (height). Places in Nigeria with high altitudes, like the Jos Plateau and Obudu, have lower temperatures (about 20°C), while the surrounding lowlands have high temperatures (over 27°C).
3. It varies with seasons. During the rainy season, temperatures are usually higher in the north but lower in the south during the dry season due to the effects of harmattan.
4. The annual range varies. The annual range of temperature in the south is 2 to 3°C, while that of the north is about 9°C.

Wind

Wind is air in motion. Nigeria is characterised by four types of wind:

1. The Tropical Maritime Air Mass (southwest trade wind): This wind comes from the Atlantic Ocean and brings the rainy season to the southern parts of Nigeria, especially around Warri and Port Harcourt, with twelve months of continuous rainfall. The rainy season in the south runs from March to October, with a short dry spell in August called the August break.
2. The Tropical Continental Air Mass (northeast trade wind): This wind is responsible for the dry season in the northern parts of Nigeria. It comes from the Sahara Desert. It is cold, dusty and dry, so it brings no rain. It brings the harmattan, a very cold, dusty and dry weather. The harmattan starts in November and ends around February.
3. Equatorial Easterlies: This wind blows around the equator from the east. It has some influence on the north-east and south-west trade winds when they meet.
4. Land and sea breeze: These local winds are restricted to the coast, for example Lagos, Warri and Port Harcourt. They blow alternately between land and sea every day.

Seasons

There are two seasons in Nigeria: the wet season and the dry season. During the wet season, the tropical maritime air mass (southwesterly wind) influences most parts of the country. During the dry season, most parts of the country are influenced by the tropical continental air mass.

Rainfall

Rainfall in Nigeria is unevenly distributed. It generally decreases from the coast inland. Along the coast, rain falls for about 8 to 12 months of the year. Further inland, the period of rainfall decreases to less than six months. The shortest periods of rainfall are in the northwest and northeast, where rain falls for less than four months of the year.

The mean annual rainfall varies from about 2000 mm along the coast to less than 600 mm in the northern part of the country.

Insolation and sunshine

Insolation is generally high throughout the year in Nigeria. Less insolation is received in the south, where cloud cover is thicker, than in the north, where there are fewer clouds. The highest amount of insolation is received in the north. Sunshine hours are fewer in the rainy season than in the dry season.

Relative humidity

Relative humidity decreases towards the north, so humidity is higher in the south than in the north. Humidity is also higher in the rainy season than in the dry season.

Evaluation

1. Define climate.
2. List four factors that affect climate.
3. State the characteristics of temperature in Nigeria.
4. Name the four types of wind in Nigeria.
5. Describe how rainfall is distributed in Nigeria.

Assignment

1. Describe the tropical maritime air mass and the tropical continental air mass, and state the season each one brings to Nigeria.
2. Explain why relative humidity is higher in the south than in the north.