Climate Variability and Change—Hydrological Impacts (Proceedings of the Fifth FRIEND World
Conference held at Havana, Cuba, November 2006), IAHS Publ. 308, 2006, 394–400.
Possible impacts of climate variability/change and
urbanization on water resources availability and quality in the Benin-Owena
River basin
J. N. OKPARA, L. E. AKEH & A. C. ANUFOROM
Nigerian Meteorological Agency, Hydrometeorological Division, PMB 615, Garki, Abuja, Nigeria
Abstract In this study, monthly rainfall and temperature from
four Nigerian meteorological stations in the Benin-Owena basin covering the
period 1940–2002, and evaporation (1960–2003) and river discharge (1980–2004)
data were obtained and analysed to investigate the impact of climatic
variability and urbanization on the water resources of the basin and the
socio-economic implications. The Benin-Owena basin is heterogeneous in nature
and located in the southwest of Nigeria. The study area covers a total land
area of 59 787 km2 and has a human population of over 13
million. Population data, the volume of solid waste generated in the region and
water quality data from 32 boreholes distributed across the area were obtained
from the UNICEF water and sanitation (WATSAN) project office and also analysed.
The analysis showed that climatic variations exist over the region that appear
as fluctuations of wet and dry periods every 2–3 years in terms of rainfall and
the river flow. Also an increasing temperature trend was observed, rising at
the rate of 0.37°C/decade. This, coupled with the high rate of
evaporation, will cause increasing water loss in the basin. The borehole
results showed that the aquifers are productive with relatively high potential
water yields. Their water quality is within the World Health Organization (WHO)
acceptable standards in terms of the physico-chemical and bacteriological
composition, except for a few boreholes located in the unplanned densely
populated areas of the basin; there, abnormal concentrations of chloride (297
mg L-1), turbidity (20FTU), iron (0.43 mg L-1) and faecal
coliform counts of 3 per 100 ml of water, occur. Re-assessment of the water quality
10 years after commissioning of the boreholes showed that 18% out of the 96% of
boreholes initially with good water quality, now had poor quality due to the
high rate of unplanned urbanization.
Key words climatic
variability; urbanization; river basin; discharge; borehole; water quality