Evidence of climatic change in Nigeria based on annual series of rainfall of different daily amounts, 1919?1985

Abstract

Annual series of light rainfall, moderate rainfall and heavy rainfall are computed for 4 zones arranged from south to north in Nigeria: Coastal, GuineaSavanna, Midland and Sahelian zones. Daily rainfall data for the period 1919-85 are utilized. Each series is examined for evidence of change in structure in terms of pattern of decrease and increase in dry and wet years, the overall trend, and the occurrence of runs of dry and wet years. The northern Nigeria (Midland and Sahel) heavy rainfall series and the Sahel moderate rainfall series are found to depict evidence of climatic change as defined by Landsberg (1975) that climatic conditions must change to a new equilibrium position with the values of climatic elements changed significantly. On the other hand Landsberg's definition of climatic fluctuations as involving temporary deflection which can revert to earlier conditions is found to fit the 4 regional light rainfall series and the Midland area moderate rainfall series. The southern Nigeria moderate and heavy rainfall series are found to depict only evidence of high frequency oscillations about a stable long-term mean. The recent drought in Nigeria north of about 9 ~ N is shown to be associated with a large decline in moderate and heavy rainfalls over this part of the country.

Variability and Trends of Daily Heavy Rainfall Events over Niger River Basin Development Authority Area in Nigeria

“…A significant decline in the frequency of all size categories at the more northerly station in Sudan was reported by Walsh et al (1988). A similar result was reported for northern Nigeria where Olaniran [14] detected a significant decrease in heavy rainfall (>25.4 mm) series for the midland and Sahel zones. A negative trend in heavy rainfall event was reported by Babatolu [15] for the Niger River Basin Development Authority Area, Nigeria during the period .…”

“…In Africa, there is an observed significant increase in intensity of extreme rainfall events between 1931-60 and 1961-90 in about 70% of South Africa [14]. A significant decline in the frequency of all size categories at the more northerly station in Sudan was reported by Walsh et al (1988).…”

Climate variability in Jordan

“…In order to avoid disadvantages of the parametric methods, non-parametric approaches such as the sequential Mann-Kendall rank test is employed in this study. The climatic trend is defined as a monotonic increase or decrease in the average value between the beginning and the end of an available time series (Olaniran, 1991). Among some non-parametric trend tests, the sequential version of the Mann-Kendall rank test has the ability to detect the beginning and/or the end of the trend.…”

Variabilité climatique et statistiques. Etude par simulation de la puissance et de la robustesse de quelques tests utilisés pour vérifier l'homogénéité de chroniques

“…Le test de corrélation sur le rang (KENDALL et STUART, 1943 ;WMO, 1966 ;OLANIRAN, 1991) Le test de corrélation sur le rang est basé sur le calcul du nombre P de paires (X;, Xj) pour lequel Xj > X s (j > i, i = 1 N -1). Sous l'hypothèse nulle (H 0 ) de stationnante de la série, la variable co définie par : Pour un risque a de première espèce donné, l'acceptation de H 0 est définie par l'appartenance de <o à l'intervalle [-U 1 _ a/2 o t , U 1-<ï/2 o t ], U 1 _ e(/2 désignant la valeur de la variable normale réduite de probabilité de non dépassement 1-a/2.…”