An overview of the gradient
Nigeria's climate is best understood as a south-to-north gradient rather than a set of sharply divided zones: conditions shift from equatorial along the coast, through a tropical middle belt, to arid and semi-arid conditions in the far north, a description the CIA World Factbook's Nigeria profile summarises simply as "equatorial in south, tropical in center, arid in north" S2. That gradient tracks the country's vegetation belts closely enough that the two are usually mapped together: the wetter forest zone in the south gives way to successive bands of savanna and finally Sahel scrubland as one moves north, with rainfall and dry-season length changing in step across the same bands — see nigeria vegetation belts for the vegetation side of this same pattern S1. Two seasons dominate nearly everywhere in the country: a wet season driven by the southwest monsoon, running roughly from April to October, and a dry season driven by the northeasterly harmattan wind, running from around November to March, though the exact onset and length of each shifts by weeks to months between the coast and the far north S1S3
The forest zone: coast and delta
Along a coastal belt 50 to 250 km wide, encompassing mangrove and freshwater swamp forest as well as lowland rainforest, annual rainfall exceeds 1,600 mm and climbs beyond 2,500 mm in the Niger Delta and along the eastern coast, among the wettest conditions anywhere in West Africa S1. This is Nigeria's shortest dry season and its most consistently humid climate, conditions that sustain the delta's mangrove forests — the largest such ecosystem in Africa — even as decades of oil spills have degraded large stretches of it; mangrove cover in the wider delta fell from roughly 10,515 km² to 8,240 km² between 2010 and 2020 S5. The Niger Delta's wetlands, spanning more than 100,000 km² across several southern states, sit at the wet extreme of Nigeria's climate range and illustrate how closely rainfall, vegetation, and settlement pattern are tied together in the far south S5
Derived and Guinea savanna: the middle belt
Moving inland, the derived savanna zone — forest converted to grassland by long-term farming and grazing — receives 1,150 to 1,500 mm of rain a year with a dry season of about three months, only slightly shorter than the forest zone itself S1. Further north, the Guinea savanna splits into a southern band, also receiving 1,150 to 1,500 mm with a four-to-five-month dry season, and a northern band receiving 1,000 to 1,250 mm with a five-to-six-month dry season, together forming the broadest single climatic belt in the country and the one most associated with Nigeria's middle-belt farming communities S1. This is the zone through which much of the river benue and the middle stretch of the river niger flow before their confluence at Lokoja, and river-basin flooding here is now tracked annually by Nigeria's hydrological authorities alongside rainfall data S4
Sudan and Sahel: the arid north
North again, the Sudan zone receives a wider and more variable 500 to 1,500 mm of rain with a five-to-seven-month dry season, while the Sahel zone in Nigeria's extreme north and northeast falls to just 250–500 mm annually with a dry season stretching seven to eight months of the year — the most arid and most seasonally extreme conditions found anywhere in the country S1. These figures place Nigeria's Sahel zone at the southern edge of the wider Sahel belt that stretches across West Africa, and they explain why drought and desertification pressure are concentrated in states such as Borno, Yobe, Jigawa, Sokoto, and Katsina, the historic core of the sokoto caliphate and, more broadly, of Hausa and Fulani pastoral and farming life — see hausa people and fulani people S1
The harmattan and the dry season
Nigeria's dry season is defined less by an absence of rain than by the northeasterly harmattan wind, a dust-laden airflow off the Sahara that peaks in December and January and brings sharply reduced humidity, hazy skies, and markedly cooler mornings, particularly across the north S3. Night-time temperatures during harmattan can fall below 10°C across much of northern Nigeria, and morning readings on the Jos Plateau and Mambilla highlands have been recorded as low as 7–15°C, making these highland areas the coldest inhabited parts of the country during the season, while southern coastal states experience a much milder version, with lower humidity but overnight temperatures that usually stay above 20°C S3. Nigeria's Meteorological Agency has reported a gradual weakening of harmattan intensity and duration over roughly the past thirty years, alongside a steady rise in average temperatures nationwide, changes researchers attribute to broader shifts in the atmospheric circulation patterns that drive the Saharan trade winds south each year S3. In some recent seasons, including one flagged by NiMet as running warmer than the long-term average, southern Nigeria has seen persistent humidity and above-average heat displace the harmattan's usual dry, dusty character altogether, a sign of the climate variability now layered on top of the country's long-standing seasonal pattern S3
Why the zones matter beyond weather
These climate bands are not simply descriptive: they set the rainfall and dry-season constraints behind Nigeria's agricultural zoning, the flood risk the Nigeria Hydrological Services Agency assesses each rainy season for river-basin states, and the ecological classification — from mangrove to Sahel savanna — that underlies nigeria vegetation belts and the country's wider physical geography discussed in geography of nigeria S1S4. Because they run in belts rather than following state or regional boundaries precisely, a single Nigerian state can straddle two zones, which is why climate descriptions of Nigeria are usually given by zone rather than by administrative unit S1