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Nigeria Climate
As in most of West Africa, Nigeria's climate is
characterized
by strong latitudinal zones, becoming progressively drier
as one
moves north from the coast. Rainfall is the key climatic
variable, and there is a marked alternation of wet and dry
seasons in most areas. Two air masses control
rainfall--moist
northward-moving maritime air coming from the Atlantic
Ocean and
dry continental air coming south from the African
landmass.
Topographic relief plays a significant role in local
climate only
around the Jos Plateau and along the eastern border
highlands.
In the coastal and southeastern portions of Nigeria,
the
rainy season usually begins in February or March as moist
Atlantic air, known as the southwest monsoon, invades the
country. The beginning of the rains is usually marked by
the
incidence of high winds and heavy but scattered squalls.
The
scattered quality of this storm rainfall is especially
noticeable
in the north in dry years, when rain may be abundant in
some
small areas while other contiguous places are completely
dry. By
April or early May in most years, the rainy season is
under way
throughout most of the area south of the Niger and Benue
river
valleys. Farther north, it is usually June or July before
the
rains really commence. The peak of the rainy season occurs
through most of northern Nigeria in August, when air from
the
Atlantic covers the entire country. In southern regions,
this
period marks the August dip in precipitation. Although
rarely
completely dry, this dip in rainfall, which is especially
marked
in the southwest, can be useful agriculturally, because it
allows
a brief dry period for grain harvesting.
From September through November, the northeast trade
winds
generally bring a season of clear skies, moderate
temperatures,
and lower humidity for most of the country. From December
through
February, however, the northeast trade winds blow strongly
and
often bring with them a load of fine dust from the Sahara.
These
dust-laden winds, known locally as the harmattan, often
appear as
a dense fog and cover everything with a layer of fine
particles.
The harmattan is more common in the north but affects the
entire
country except for a narrow strip along the southwest
coast. An
occasional strong harmattan, however, can sweep as far
south as
Lagos, providing relief from high humidities in the
capital and
pushing clouds of dust out to sea.
Given this climatological cycle and the size of the
country,
there is a considerable range in total annual rainfall
across
Nigeria, both from south to north and, in some regions,
from east
to west. The greatest total precipitation is generally in
the
southeast, along the coast around Bonny (south of Port
Harcourt)
and east of Calabar, where mean annual rainfall is more
than
4,000 millimeters. Most of the rest of the southeast
receives
between 2,000 and 3,000 millimeters of rain per year, and
the
southwest (lying farther north) receives lower total
rainfall,
generally between 1,250 and 2,500 millimeters per year.
Mean
annual precipitation at Lagos is about 1,900 millimeters;
at
Ibadan, only about 140 kilometers north of Lagos, mean
annual
rainfall drops to around 1,250 millimeters. Moving north
from
Ibadan, mean annual rainfall in the west is in the range
of 1,200
to 1,300 millimeters.
North of Kaduna, through the northern Guinea savanna
and then the
Sudan (see Glossary)
savanna zones, the total rainfall
and
the length of the rainy season decline steadily. The
Guinea
savanna starts in the middle belt, or southern part of
northern
Nigeria. It is distinguished from the Sudan savanna
because it
has more trees whereas the Sudan few trees. Rainy seasons
decline
correspondingly in length as one moves north, with Kano
having an
average rainy period of 120 to 130 days, and Katsina and
Sokoto
having rainy seasons 10 to 20 days shorter. Average annual
rainfall in the north is in the range of 500 to 750
millimeters.
The regularity of drought periods has been among the
most
notable aspects of Nigerian climate in recent years,
particularly
in the drier regions in the north. Experts regard the
twentieth
century as having been among the driest periods of the
last
several centuries; the well publicized droughts of the
1970s and
1980s were only the latest of several significant such
episodes
to affect West Africa in this century. At least two of
these
droughts have severely affected large areas of northern
Nigeria
and the Sahel region farther north. These drought periods
are
indications of the great variability of climate across
tropical
Africa, the most serious effects of which are usually felt
at the
drier margins of agricultural zones or in the regions
occupied
primarily by pastoral groups.
Temperatures throughout Nigeria are generally high;
diurnal
variations are more pronounced than seasonal ones. Highest
temperatures occur during the dry season; rains moderate
afternoon highs during the wet season. Average highs and
lows for
Lagos are 31° C and 23° C in January and 28° C and
23° C
in June.
Although average temperatures vary little from coastal to
inland
areas, inland areas, especially in the northeast, have
greater
extremes. There, temperatures reach as high as 44° C
before the
onset of the rains or drop as low as 6° C during an
intrusion of
cool air from the north from December to February.
Data as of June 1991
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