When the dry season comes

The dry season is longest in the north and shortest in the south. The table uses NiMet's long-term monthly averages, published on the World Meteorological Organization's weather service, to show the months that average under 10 mm of rain at ten weather stations, from north to south, and the hottest month: the one with the highest average daily maximum temperature.

Most of the averages cover 1981 to 2010 or 1991 to 2020; the pages for Abuja, Lagos and Port Harcourt do not give a period. Any one year can differ, so plan with the table and adjust with your own records.

Weather station	Months averaging under 10 mm of rain	Hottest month
Sokoto	November to April	April
Kano	November to March	April
Maiduguri	November to March	April
Yola	November to March	March and April
Abuja	November to February	March
Ilorin	December to February	March
Enugu	December and January	February
Benin City	None; least rain in December and January	February
Lagos	None; least rain in December and January	February
Port Harcourt	None; least rain in December and January	February

Need rises as the water falls

A crop's water need depends on the weather and on how far the crop has grown. FAO's manual puts the highest needs where it is hot, dry, windy and sunny, and the lowest where it is cool, humid and cloudy. A young crop needs about 50 percent of what it will need at full growth, and its need peaks as it reaches full size.

In the north the harmattan blows through much of the dry season: a dry, dusty wind from the Sahara, with low humidity and cooler nights, which FAO says may last from October to May. The hottest weeks come at the end, just before the rains (see the table).

Meanwhile the water falls. FAO notes that many smaller rivers, especially in the north, are seasonal, and the British Geological Survey reports groundwater levels falling in the dry season, most of all in hard-rock (basement) areas where the ground holds little water. So the weeks before the rains are when water need is high and the source is at its lowest.

The first rains do not end the problem at once. A study of a village in semi-arid north-eastern Nigeria found the start of the rainy season a precarious time, when none of its water sources could be relied on.

Sources: FAO (1986), Irrigation Water Management Training Manual No. 3: Irrigation Water Needs, Part I, chapter 2, sections 2.1 and 2.3; FAO (1994), Aquatic plants and wetland wildlife resources of Nigeria, CIFA Occasional Paper 21: chapter 1 and section 1.1, Climate; FAO (2016), AQUASTAT Country Profile: Nigeria, water resources and irrigation sections; British Geological Survey (2018), Africa Groundwater Atlas: Hydrogeology of Nigeria, groundwater status; Tarhule and Woo (2002), Adaptations to the dynamics of rural water supply from natural sources: a village example in semi-arid Nigeria, abstract.

The dry season at a glance

End of the rains: water in wells and rivers is near its highest
The harmattan: dry, dusty air and cool nights
The crop grows, and each week it needs more water
The water level in wells and rivers falls through the dry season
The hottest weeks, just before the rains: water need is high while the water is lowest
The first rains: early in the season, sources may not recover at once

Through the dry season the crop needs more water each week while the wells fall, so the last weeks before the rains are the hardest.

Check your source at its lowest

Plan on what your source gives at the end of the dry season, not at the start. Measure it late in the season, or ask for a pumping test made then: a figure taken just after the rains can overstate what the same well or borehole gives in the last weeks. FAO's handbook asks designers for the water a source gives when it is at its lowest, by the hour and by the day, and that is the figure to design on.

Ask neighbours with wells or boreholes nearby how their water held up in past dry seasons, and whether any ran dry. For a river or stream, note how far it shrank, or whether it stopped.

How to measure what a source gives Choosing a pump for your water source

Sources: FAO (2007), Handbook on Pressurized Irrigation Techniques, chapter 19: Engineering investigation, farm data sheet; British Geological Survey (2018), Africa Groundwater Atlas: Hydrogeology of Nigeria, groundwater status.

Power for the whole season

Count the hours of pumping the hottest weeks will need, and check that your power can deliver them every day: grid hours, generator fuel, or sunshine.

FAO's profile notes that many public irrigation schemes in Nigeria are under-used because of high running costs, fuel shortages and worn-out pumps. Service the pump before the season, and keep fuel and spare parts in hand.

Solar pumps run only while the sun shines, and the harmattan's dust settles on the panels. A modelling study of solar power in West Africa estimated that dust can cut panel output by more than 50 percent at the worst-affected places in the harmattan season, so plan to clean the panels often in those months.

Solar pump sizing checklist Irrigation pumping

Sources: FAO (2016), AQUASTAT Country Profile: Nigeria, water resources and irrigation sections; Isaacs and others (2023), Dust soiling effects on decentralized solar in West Africa, Applied Energy 340: abstract.

Storage to bridge the gaps

A tank lets a slow source fill through the day and night, and lets you water when power is there rather than only while the source is running. Size it on the need in the hottest weeks, not the first ones.

If you rely on tankers or town supply, agree deliveries before the season starts, and check that the tank holds enough to cover the gaps between them.

Sizing an irrigation storage tank

A month-by-month plan

Written for the north and the middle belt, where the dry season is longest. In the south the driest months are December and January, and the hottest is February (see the first table).

Month	What is happening	What to do
September and October	The rains are ending in the north, and later further south	Decide the crop and the area. Service the pump, and order filters, spare parts and fuel. Agree any water deliveries.
November	The dry season is under way across the north	Measure the source and note the date. Plant or start watering. Clean the filters after the first runs.
December to February	Harmattan: dry, dusty air and cool nights	Water to the crop's growing need, and check the soil before each watering. Clean dust off solar panels.
March and April	The hottest months in the north and the middle belt, with sources at their lowest	Measure the source again and keep the tank full. Watch for wilting in the afternoon. Keep fuel and spares in hand.
May and June	The first rains in the north; they start earlier further south	Keep watering until the rains settle, since early rains stop and start. Then flush the lines and service the system.

Sources: NiMet and WMO (2026), World Weather Information Service: Kano climate; NiMet and WMO (2026), World Weather Information Service: Abuja climate; FAO (1994), Aquatic plants and wetland wildlife resources of Nigeria, CIFA Occasional Paper 21: chapter 1 and section 1.1, Climate; British Geological Survey (2018), Africa Groundwater Atlas: Hydrogeology of Nigeria, groundwater status; Usman and Mamman (2022), Spatio-temporal analysis of dry spell for agricultural decision support in north-central Nigeria, Environmental and Earth Sciences Research Journal 9(1): results.

Before the season starts

You know your station's dry months and hottest month, from the table or from NiMet
You have measured your source, and will measure it again in the hottest weeks
You know the crop and the area, and when the crop will be at full growth
The pump has been serviced, and you hold spare parts, filter elements and fuel
Your power can run the pump for the hours the hottest weeks need
Your tank, if you have one, is full before the hours you water
Someone is in charge of daily checks, and knows what to do if water runs short
You have decided what to cut back first if water runs short

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Next step

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Planning dry-season irrigation in Nigeria, month by month.