Climate is the average weather condition of the atmosphere over a very long period of time. The elements of climate – rainfall, temperature, wind, relative humidity, pressure, cloud cover and sunshine.
Temperature: Temperature is defined as the degree of hotness or coldness of a place. The temperature in Nigeria is not uniform and it has the following characteristics.
- It varies from place to place: Temperature is low (24˚C) in the south because of the cooling effects of the Atlantic Ocean while it is high in the north with over 28˚C because of the distance from the sea.
- It varies with altitude: Place on high altitude like Jos, Obudu, Adamawa, etc. tend to have lower temperature (20˚C) while the neighbouring lowlands have temperature of over 27˚C.
- It varies with seasons: Temperatures are usually higher during the rainy season in the north but low in the south during dry season due to the influence of harmattan.
- Variation in annual range: The annual range of temperature in the south is between 2 – 3˚C while that of the North is 9˚C.
Wind: Wind is defined as air in motion. There are four local types of winds in Nigeria. These are:
- Tropical Maritime Airmass (South West Trade Wind): This trade wind is responsible for rainy season. It blows across the Atlantic Ocean towards the coast of Nigeria. The wind is warm and wet; hence, it brings rainfall to Nigeria with the wettest part in the delta region- Warri and PortHarcourt having twelve months of rainfall. The rainfall decreases towards the north. It usually starts around March and ends around October with a short dry period in August called August break.
- Tropical Continental Airmass (North East Trade Wind): This trade wind is responsible for the dry season. It blows across the Sahara desert towards Nigeria. It is cold, dusty and dry; hence, it does not bring rain. Rather, it brings very cold, dusty and dry weather called It starts from November and ends around February.
- 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. The North East and South West trade winds meet along a slanting surface where they continuously rub against each other. This surface is called Intertropical front. The area above this front, where the two air masses to some extent mix as a result of rubbing, is called the Intertropical Convergence Zone (ITCZ). This zone is not fixed. It can move north or south depending on which of the two air masses is stronger. When the Equatorial Easterlies cut below the South West trade wind, they cause torrential rainfall accompanied by lightning and thunder. This rainfall is called Line Squall. When the Equatorial Easterlies cut below the North East trade winds, they cause whirling, cyclical winds, carrying dusts and pieces of papers. This wind is called Dust devil.
- Land and Sea Breezes: These local winds are restricted to the coasts of Lagos, Warri, Port Harcourt, etc.
- These are local winds which blow alternately between land and sea on daily basis.
- Breeze exchange between the land and the sea is attributed to differential heating of the land and sea.
- These winds are common in areas very close to the sea.
Sea Breeze: This breeze blows from the sea to the land. During the day, the land is heated much faster than the sea and it is cooler than the sea at night. As the land is heated during the day, it causes the air to rise, creating a low pressure situation. Air therefore, blows from the sea to replace heated and rising air on the land, thereby resulting in lower temperature and relatively cool air on the land which results in sea breeze.
Land Breeze: This breeze blows from the land to the sea. At night, the land becomes cooler than the sea, having lost much of its temperature at a much faster rate than the sea. Thus, there is a high pressure situation on the land and a relatively lower pressure situation on the sea. Hence, land breeze blows from the land to sea.
Rainfall Distribution in Nigeria
- Rainfall in Nigeria is not uniformly distributed.
- It is higher in the south due to its nearness to the sea and the effect of South West trade wind while it is lighter in the north.
- Rainfall decreases from the south (3000mm) towards the north (300mm).
- Highland areas like Jos, Adamawa, etc. receive higher rainfall than the neighbouring areas as a result of relief or orographic type of rainfall.
- Rainfall varies with season. Rainfall is heavier during the rainy season (March – October) than in dry season (November – February).
- In the south, there are two peaks of rainfall (also called double maxima) which are around June/July and September/October while the north has only one peak of rainfall (also called single maximum).
Seasons in Nigeria
There are two types of seasons in Nigeria. These are dry season and rainy season.
- Wet or Rainy Season: The wet season occurs between March and November.
Characteristics of Wet Season
- High temperature: Temperature is higher in the north (33˚C) than the south (27˚C) due to the effect of the sun, being at the tropic of Cancer in June, thus making the north to be hotter while the moderating effect of the ocean reduces the temperature in the south in June.
- Low pressure: There is low pressure in the north due to high temperature in the Sahara in June and a high pressure in the south in June.
- Prevailing wind: The prevailing wind is the tropical maritime air mass or the South West trade wind which blows from the high pressure belt area in the south in June to the low pressure belt in the north. This then pushes the tropical continental air mass towards the north where the intertropical front is formed.
- Heavy rainfall: The heaviest rainfall occurs in West Africa during this wet season. As a result, the south experiences double maxima of rainfall while the north experiences a single maximum. Rainfall decreases from the south towards the north.
- Dry Season: The dry season occurs between November and February.
Characteristics of Dry Season
- Low temperature: During this season, the temperature is usually low because the sun is now overhead in the southern hemisphere; hence, the temperature is lower in the north while it is higher in the south.
- High pressure: The pressure system is also reversed. There is high pressure in the north and low pressure in the south in January.
- Prevailing wind: The prevailing wind is the tropical continental air mass or the North East trade wind. This wind then pushes the South West wind further towards the coast where the tropical front is now formed.
- Absence of rainfall: The tropical continental air mass blows from the high pressure area of the Sahara desert and since it blow offshore. It does not bring rain to West Africa.
- Harmattan: The dry season brings harmattan which is experienced between December and January. The harmattan is cold, dry, dusty and hazy.
Types of Climate in Nigeria
There are four climate types in Nigeria. These are:
- Sub-equatorial climate (South).
- Tropical hinterland (Tropical wet).
- Tropical continental (Tropical dry).
- High plateau climate.
- Sub-equatorial Climate
- It is found in the south, in places such as Warri, Lagos, Calabar, PortHarcourt, etc.
- It has heavy rainfall of over 2500mm per annum.
- It has double maxima of rainfall – June/July and September/October with convectional type of rainfall.
- There is no month without rainfall of at least 50mm.
- It has high temperature of about 27˚C.
- It has low annual range temperature i.e. 2 – 3˚C.
- It has a high relative humidity of over 90%.
- It has long period of wet or rainy season between 6 – 8 months and 3 – 4 months of dry seasons.
Effects of Sub-equatorial Climate on Agriculture
- Heavy rainfall gives rise to the growth of tree crops like cocoa, rubber, oil palm, kolanuts, etc.
- Heavy rainfall also gives rise to the growth of tuber crops like yam, cassava, potatoes, etc.
- Heavy rainfall (i.e. two peaks of rainfall) gives rise to double cropping i.e. two planting seasons in March and September e.g. early maize and late maize.
- Heavy rainfall and thunderstorm give rise to leaching and soil erosion.
- Heavy rainfall supports thick growth which is difficult to weed, cut down trees and generally it leads to reduction in the size of farmlands.
- Heavy rainfall and high humidity which give rise to forest, hinder rearing of cattle because of lack of grasses and high incidence of Tsetse flies.
- Tropical Hinterland (Wet) Climate
- This climate is found in the forest areas like Ibadan, Ilorin, Akure, Oshogbo, Enugu, etc.
- It has moderate rainfall of 2000 – 3000mm.
- It has 4 – 5 months of little rainfall i.e. the wet season is roughly 6 – 7 months of the year.
- It has double maxima of rainfall in the southern boundary and single maximum in the northern boundary.
- It has high temperature of over 27˚C.
- It has an annual range of temperature of 6˚C.
Effects on Agriculture
- Moderate rainfall gives rise to the growth of crops found in both north and south.
- Moderate rainfall gives rise to the growth of yam, cassava, cocoyam, millet, sorghum, etc.
- Both root crops like yam and grain crops like rice, maize, millets are grown.
- Light rainfall in the northern boundary gives rise to livestock production.
- Tropical Continental (Dry) Climate
- This is also called the Sudan climate.
- The climate is found in Sokoto, Bauchi, Kano, Bornu, etc.
- Rainfall is between 500 – 1000mm per annum.
- There is a long period of little or no rainfall (i.e. dry season of 4 – 8 months).
- The relative humidity is low (20 – 40%) in January and (50 – 60%) in July.
- High temperatures throughout the year (21˚C – 33˚C).
- It has a high range of temperature – (11˚C).
Effects on Agriculture
- Little rainfall brings about irrigation farming around Kima – Sokoto basin, Hadeija – Jaima basin, etc.
- Little rainfall favours the growth of grain crops like maize, rice, millet, sorghum, etc.
- Little rainfall supports livestock production like cattle, sheep and goats.
- Little rainfall encourages wind erosion.
- High Plateau Climate
- This climate is found around highland areas like Jos, Adamawa, Obudu, Mambilla Plateau.
- It has heavy rainfall around Jos and its environs with 2000mm.
- It has moderate temperature between 21˚C and 26˚C.
- Temperature range is between 8˚C – 12˚C.
- It has a high relative humidity.
Effects on Agriculture
- Heavy rainfall leads to contour ploughing.
- Heavy rainfall supports the growth of tree crops like coffee.
- Moderate rainfall in the lowland supports the growth of grasses for cattle rearing.
- Absence of pests e.g. Tsetse flies promotes livestock production.
Relationship between Climate (Rainfall) and Agricultural (Farming) Activities
There is a positive relationship between climate or rainfall distribution and farming or agricultural activities in Nigeria.
- In the Forest Vegetation Belt (Sub-equatorial climate) of Southern Nigeria.
- Rainfall throughout the year results in all-year round cropping.
- Heavy rainfall 150-200cm results in the growth of tree and root crops.
- Heavy rainfall and humid conditions result in difficulties in animal rearing.
- Heavy rainfall promotes the growth of weeds. This results in weeding the farm almost throughout the year.
- Early rains in March/April result in planting in March/April.
- Two peaks of rainfall give rise to double cropping in a year.
- Light rains and heavy sunshine in November to February result in clearing and burning of bush.
- In the Savanna Vegetation Belt (Tropical Continental Climate) of Northern Nigeria
- Rainfall from April to August leads to planting of crops from April to August.
- Little amount of rainfall (50-150cm) in a year favours the growth of grasses.
- Little amount of rainfall (50-150cm) in a year, favours the cultivation of rice, maize, millet, groundnut, etc. which does not require heavy rains.
- Little rain under 50cm from September to March and drying of grasses lead to movement of cattle farmers and their herds from the north to the south.
- Little rain under 50cm from September to March leads to irrigation of crops in farms near water courses.
- Little rain and heavy sunshine from September to December favour drying and storage of crops.