On the annual and seasonal patterns of rainfall fluctuations in sub‐saharan West Africa

Abstract

Monthly rainfall data for 16 stations in Nigeria were collected for the period . From this, the annual, the wet season, the onset, the peak, and the retreat rainfall data were derived. The patterns of fluctuations of rainfall were analysed therefrom. The series were first examined for trends and then for periodic fluctuations. Trend analysis revealed that a majority of the series exhibit negative trends, and in some cases the trends were significant. For all the series analysed, there is the general tendency towards increasing aridity. Spectral analysis indicates prominent periods of between 2-and 8-year cycles. Other periodicities observed include 1 6 , 18-, and 21-year cycles.

Towards a wetter Sudano‐Sahelian ecological zone in twenty‐first century Nigeria

“…Of the known factors influencing the climate of West Africa in general, and Nigeria in particular, the northward and southward migration of the ITD and its associated air masses (mT and cT) appear to be the most popularly accepted (Lamb, 1983;Adejuwon et al, 1990;Odekunle, 2004;Adejuwon and Odekunle, 2006). It has been established that rain falls mostly when an area is overlain by the mT air mass and ceases when the area is overlain by the cT air mass, thereby making the latitudinal position of the ITD a strong determinant of most rainfall attributes.…”

“…Short-term and long-term trends that recur regularly can thus be referred to as shortterm and long-term periodicities, respectively. A review of the literature indicates apparent evidence of rainfall trends and periodicities in West Africa (Hutchinson, 1985;Adejuwon et al, 1990;Folland et al, 1991).…”

“…Many studies on the Sudano-Sahelian ecological zone (SSEZ) of West Africa in general, and Nigeria in particular, have established a general trend in rainfall towards aridity (Adejuwon et al, 1990;Folland et al, 1991;Nicholson, 2001;Hulme et al, 2001). Recently however, some scenarios (based on greenhouse gas emissions) have suggested that the observed trend towards aridity will be put on hold or be reversed in the twentyfirst century (MEFRN, 2003;Haarsma et al, 2005;Adejuwon, 2006).…”

Relating seasonal dynamics of enhanced vegetation index to the recycling of water in two endorheic river basins in north-west China

“…Most methods used in establishing the onset and cessation of the precipitation season usually aim to determine the effective planting date of crops (Adejuwon et al, 1990;Adejuwon and Odekunle, 2006;Benoit, 1977;Ilesanmi, 1972). In these methods, the onset and end of the precipitation season is equated to the onset and end of the growing season (Benoit, 1977;Odekunle et al, 2005).…”

“…These methods do not help clarify the relationship between the onset of the growing and precipitation seasons, when the seasons are not entirely synchronised. Cumulative % precipitation (Ilesanmi, 1972) is the most widely used indicator of the onset and cessation of the precipitation season independent of other climatic and vegetation factors (Adejuwon et al, 1990;Adejuwon and Odekunle, 2006;Odekunle, 2006). In this method, daily % precipitation data are processed to generate 5-day means.…”