Nigeria is located between Latitude 4° and 14°N and Longitude 2°45' and 14°30'E. To the north, the country is bounded by the Republics of Niger and Chad, in the west by the Republic of Benin, in the east by the Republic of Cameroon, and to the south by the Atlantic Ocean. Approximately 13,000 km2 of the land is covered by water (1.4%) and the remaining 98.6% of the land cover ranges from thick mangrove forests and dense rain forests in the south to a near-desert condition in the northeastern corner of the country. The country takes its name from its most prominent river, the Niger. Nigeria has a land area of about 910,770 km2 (Adeyinka et al., 2005); a north-south length of about 1,450 km and a west-east breadth of about 800 km. Its total land boundary is 4,047 km while the coastline is 853 km.
Nigeria is located primarily within the lowland humid tropics just north of the equator and is generally characterized by a high-temperature regime almost through the year. In the far south, mean maximum temperature is about 32°C while in the north it is 41°C. However, the mean minimum temperature is 21°C in the south and under 13°C in the north which has a much higher annual range. The mean temperature for the country is 27°C, in the absence of altitudinal modifications. Over the last few decades, there has been a general increase in temperature throughout Nigeria (UNFCC, 2003).
Nigeria, by virtue of its location, experiences a warm tropical climate with two seasons - the rainy or wet season that lasts from mid-March to November in the south and from May to October in the north; and the dry season occupies the rest of the year (Oyenuga, 1967).
The Nigerian climate varies from tropical in the coastal area to sub-tropical up north. There are two regimes of climate: a dry season and a wet season. The seasonal pattern of climatic conditions over Nigeria gives rise to four seasons in the south and two in the north. This is the result of annual total rainfall occurrence and distribution, which is more predominant in the south than in the north. The mean annual rainfall along the coast in the southeast is 4000 mm while it is only 500 mm in the northeast.
Southern Nigeria: The four observed seasons are
• The long rainy season: This starts in February/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 region and the coastal lowlands.
• The short dry season: This is experienced in August for 2-3 weeks known as 'August break.'
• The short rainy season: This brief wet period follows immediately after 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 long dry season: This period starts from late October and lasts till early March with peak dry conditions between early December and late February. The period witnesses the prevailing influences of the dry and dusty northeast winds, as well as the 'harmattan' conditions.
Nigeria can, thus, be broadly divided into the following climatic regions:
(a) the humid sub-equatorial, in the southern lowlands
(b) the hot tropical continental, in the far north
(c) the moderated sub-temperate in the high plateaus and mountains
(d) the hot, wet tropical, in the hinterland (the middle belt) (Online Nigeria, 2002).
In general there are fewer dry season in the extreme southern tip of the country, the wet season often does not exceed 5 months in the northeastern part. Similarly annual rainfall totals range from 2,500 mm in the south to less than 400 mm in parts of the extreme north (FMEN, 2001).
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