Although Nigeria lies wholly within the tropical zone, there are wide climatic variations in different areas of the country. Near the coast, the seasons are not sharply defined. Temperatures rarely exceed 32°C (90°F), but humidity is very high and nights are hot.
Inland, there are two distinct seasons: a wet season from April to October, with generally lower temperature, and a dry season from November to March, with midday temperatures that surpass 38°C (100°F) but relatively cool nights.
The Long Rainy Season:This starts in March and lasts to the end of July, with a peak period in June over most parts of southern Nigeria. It is a period of thick clouds and is excessively wet particularly in the Niger Delta and the coastal lowlands. It is marked by humidity with values hardly below 85 per cent in most parts of the forested south.
The Short Dry Season:This is experienced in August for 3-4 weeks. However, the real dry period known as the “August break” is generally observed in the last two weeks of August in most parts of southern ” Nigeria”.
The Short Rainy Season:This brief wet period follows the “August break” from early September to Mid-October, with a peak period at the end of September. The rains are not usually as heavy as those in the long rainy season, although the spatial coverage over southern Nigeria is similar.
The two periods of rainfall intensity give the double maxima phenomenon of the rainy season characteristic of southern Nigeria. The short dry season in August between these two rainy periods allows for harvesting and planting of fast-growing varieties of grains, such as maize.
The Long Dry Season:This period starts from late October and lasts to early March with peak dry conditions between early December and late February. The period witnesses the prevailing influences of the dry and dusty north-east winds, as well as the ‘harmattan’ conditions. Vegetation growth is generally hampered, grasses dry and leaves fall from deciduous trees due to reduced moisture.
The climatic conditions in the northern part of Nigeria exhibit only two different seasons, namely, a short wet season and a prolonged dry season. Temperatures during the day remain constantly high while humidity is relatively low throughout the year, with little or no cloud cover.
There are, however, wide diurnal ranges in temperature (between nights and days) particularly in the very hot months. The mean monthly temperatures during the day exceed 36°C while the mean monthly temperatures at night fall, most times, to below 22°C.
Thus much of Nigeria and the region to the west experiences two rainy periods as the intertropical convergence moves north or south; but in the north the two rainy seasons merge to give a single wet season between July and September.
The few high plateaus of Jos and Biu, and the Adamawa highlands, experience climatic conditions which are markedly different from the generalised dry and wet period in northern Nigeria. Temperatures are 5 – 10°C lower due to high altitude than in the surrounding areas. Similarly, the annual rainfall figures are higher than in areas around them, particularly on the windward side.