Rainfall anomaly patterns in dry and wet years over Nigeria

Abstract

Rainfall amount and rainfall frequency for five individual dry and five individual wet years were compared with the 1941-1987 averages for Nigeria. Five spatial-anomaly types were found to emerge for dry years, namely above average rainfall in southern Nigeria but below average rainfall in northern Nigeria (spatial type I), above average rainfall in the centre but below average rainfall in the coastal and extreme northern parts of the country (spatial type 11) and below average rainfall in southern Nigeria but above average rainfall in northern Nigeria (spatial type 111). The other two anomaly types are country-wide occurrence of below average rainfall (spatial type IV) and country-wide occurrence of above average rainfall (spatial type V). These spatial-anomaly types also hold true for wet years, except that the spatial type I1 is replaced by the Occurrence of below average rainfall in the centre but above average rainfall in the coastal and extreme northern parts of the country (spatial type VI).The spatial type I and I1 anomalies support the hypothesis of a restricted northward advance of the Inter Tropical Discontinuity (ITD) in dry years and on a complementary basis the spatial patterns for the rainfall amount anomaly (RAA) and the rainfall frequency anomaly (RFA) depicted these two anomaly types in 40 per cent of the monthly periods for the set of dry years considered. The spatial type IV anomaly, which occurs during the peak of the rainy season, supports the hypothesis of a weakening of the rainy season intensity and on a complementary basis the spatial patterns for the RAA and the RFA depicted this pattern in 30 per cent of the monthly periods for the dry years studied. This shows that both hypotheses are valid for explaining dry years in subtropical West Africa.The spatial type I11 and V anomalies support the hypothesis of a considerable northward incursion of the ITD in wet years. It was found that the spatial patterns of the RAA depicted these anomaly types in 53.3 per cent of the monthly periods whilst the spatial patterns of the RFA depicted the anomaly types in 66.7 per cent of the monthly periods for the set of wet years considered.

Irrigation Schedules for Selected Food Crops Using Water Balance Book-Keeping Method

“…The study area generally experiences moisture deficit from January to early March with an annual moisture deficit value of 312.5 mm. Some previous rainfall reports have confirmed similar trends in rainfall and soil moisture patterns over southern Nigeria (Olaniran, 1990(Olaniran, , 1991Jayeoba, 2011).…”

Identification of deficiencies in seasonal rainfall simulated by CMIP5 climate models

“…The preceding discussion thus highlights two likely causes of model bias in the representation of the West African Monsoon and provokes a number of additional questions. Further detailed analysis of such mechanisms is merited, along with other LDS drivers, including the deflection of south-westerly winds to westerly winds (Olaniran 1989), which could be addressed through idealized model integrations and further analysis of observations.…”

Effect of climate variability on the yield of crops in Ondo State, Nigeria

“…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 (Olaniran, 1991a;Salami and Matthew, 2009;Osang et al, 2015). These drought periods are indications of the great variability of climate across tropical Africa and 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.…”