Rainfall Variability during Onset and Cessation of the Growing Season in the Sudano-Sahelian Region of Nigeria
Keywords:Rainfall, onset, cessation, Sudano-Sahelian, Nigeria
Onset and cessation of rainfall is fundamental to crop production, especially in areas with variable climate and predominance of rain-fed farming practice. This paper, therefore, examined rainfall trends during onset and cessation of the growing season in the Sudano-Sahelian region of Nigeria using 64 years (1951-2014) rainfall data for 8 synoptic weather stations (Sokoto, Gusau, Katsina,
Kano, Potiskum, Nguru, Maiduguri and Yola). Simple regression was used to analyse the trends of rainfall during the onset and cessation. The results revealed that rainfall declined in Katsina, Nguru and Yola at annual rates of -0.036 mm, -0.197mm and -0.143 mm respectively during the onset while Sokoto, Kano, Potiskum and Maiduguri witnessed increase at annual rates of 0.040
mm, 0.188 mm, 0.269 mm, 0.026 mm and 0.025 mm respectively. Sokoto, Katsina, Potiskum, Nguru and Yola experienced decreasing rainfall trend at annual rates of -0.232 mm, -0.112 mm, -0.082 mm, -0.153 mm and -0.360 mm respectively during cessation while Kano and Maiduguri recorded increase at annual rates of 0.180 mm, 0.246 mm and 0.037mm respectively. Rainfall trends were significant in Kano and Yola during onset and cessation respectively. The mean rainfall of 1983-2014 negatively deviated from that of 1951-1982 in Kano during onset and cessation while the negative deviation in Sokoto and Potiskum was only recorded during onset. While the rainfall pattern shows increasing spatial variation during onset of the growing season, generally it is more varied during cessation. The paper recommends early maturing crops, irrigation and/or staggering of planting in line with prevailing rainfall trends during onset and cessation, especially in Sokoto, Katsina, Potiskum, Nguru and Yola.