By Akintola Omigbodun (Dr)

February and March have been observed to be the hottest months of the year in Nigeria and the rest of West Africa. However, this year in the Lagos area, we have had three noticeable rainfall events during January and we have, in early February, been experiencing the cooler temperatures brought about by the harmattan.

The long-term average rainfall in the Lagos area for January is less than 25mm but the rainfall experienced in January 2013 is more than this long-term average. Can we because of these January rains say that the climate is changing?

We should understand, in the first place, that the climate over Nigeria and the rest of West Africa has several features. The annual rainfall in the region decreases in magnitude as one goes from the coast in the South to the border with the Sahara Desert in the north.

There are two main seasons – the rainy season and the dry season. The rainy season occurs between April and October in the south while in the north, the start of the rainy season is delayed till June. The climate observed is the result of the interactions between the ocean, the land and the atmosphere.

There are two air masses, the Equitorial Maritime and the Tropical Continental and the boundary between these two air masses is called the Inter Tropical Front, ITF, and this boundary stays to the north of the equator all year round. The Equitorial Maritime air mass is characterized by southwesterly winds coming to land off the Gulf of Guinea and these are the main rain bearing winds in Nigeria.

The Tropical Continental air mass is the dry northwesterly winds known as the harmattan. The rainy season occurs all over Nigeria when the ITF has retreated to beyond the northern boundary of Nigeria and the whole country is traversed by southwesterly winds.

The dry season occurs when northeasterly winds cover the whole of the northern part of the country and may even break through to the coast on a few days during the height of the season as we have experienced in Lagos during early February 2013.

Other factors that determine our climate are humidity, air temperature and pressure, wind speed and direction, cloud cover and types, amount and form of precipitation, infrared and solar radiation, terrestial radiation, soil moisture, evaporation, vegetation cover, latitude, elevation and sea surface temperature. There are variations in all the factors we have just mentioned above from one year to the next year with the result that we have years of heavy rainfall, the wet years, and years of low rainfall, the dry years.

In a study of rainfall fluctuations in West Africa for the period of 1901 to 1990, the average of annual rainfalls for the period was used as a baseline against which annual rainfalls were plotted and compared. It was observed that annual rainfall levels from 1971 to 1990 were significantly low compared to the long-term average.

Another study at Ahmadu Bello University of rainfall in Northern Nigeria covered the area north of latitude 100N with data from Kontagora, Kaduna, Bauchi, Gombe, Yelwa, Samaru, Poliskum, Birnin Kebbi, Gusau, Kano, Maiduguri, Sokoto, Katsina, Hadejia and Nguru.

Rainfall data for the period 1976 to 2005 was analysed and the results showed that the rains now start late but end early and thus the length of the rainy season is decreasing. The frequency of dry spells of 5 days is decreasing, while dry spells of 10, 15 or more days are on the increase.

Northern Nigeria is therefore becoming drier. Professor O. J. Olaniran gave an inaugural lecture at the University of Ilorin entitled Rainfall Anomalies in Nigeria: the Contemporary Understanding. Rainfall data for Nigeria for the period 1921 to 1985 was considered. One of the conclusions was that in Southern Nigeria, there is evidence that the climate oscillates frequently between wet years and dry years.

The Nigerian Meteorological Agency, NIMET, has carried out a review of the climate over Nigeria in 2010. The review indicated that warmer than normal conditions prevailed over greater parts of the country. It was also found that rainfall amounts in 2010 over the country were generally higher than long-term mean values.

Rainfall data provided by NIMET for Iseyin and Sahki in Oyo North for the period 1990 to 2010 show a pattern of wet years followed by dry years. Maximum rainfall was at 4-year intervals, with a minimum two years after a maximum.

There was noticeable drought in the northern parts of West Africa between 1968 and 1973 and there was a Drought Relief Committee in Nigeria. We have mentioned earlier that in the period following on the drought, West Africa had lower than average rainfall. The rainfall that has been observed in 2010, 2011 and 2012 in Nigeria would suggest that we might be in a period of higher than average rainfall.

Whether the rainfall we have experienced in the last few years follows the natural variability between wet years and dry years or the rainfall is a reflection of climate change, our communities should be able to cope adequately with the levels of rainfall we are experiencing.

Current rainfall levels are not higher than what has been observed at various times over the last 100 years. We will examine in the weeks ahead what can be done to prevent floods or mitigate the effects of floods in some of our communities. .