Journal of Emerging Trends in Engineering and Applied Sciences: Research Areas

Article Title: Heavy Rainfall/Flash Flood Events Forecasting in Africa: Nigeria as a Case Study
by Ikenna C. Orisakwe, Bob Alex Ogwang and Leon Guy Razafindrakoto

Abstract:
For a good and effective forecast of heavy rainfall/Flash flood risk over Africa, an attempt has been made to determine the effective threshold for the forecast of heavy rainfall/flash flood risks, using Nigeria as a case study. The threshold rainfall amount that qualifies a 24-hour rainfall event to be a heavy or extreme rainfall event over each of the cities studied for efficient weather-related disaster risk management, were made using the value associated with a specific percentile of the daily rainfall value. This was carried out using sets of daily rainfall data that varied from 30 to 40years. Simple linear regression, trend analyses, relative percentage occurrence, frequency and percentage contributions (intensity) of heavy rainfall to the cumulative rainfall were calculated and plotted. From the result, there is evidence of temporal variability on the seasonal and inter-seasonal analyses of the HRF, such that out of 37 cities studied, 26 cities recorded an increase in the percentage occurrence of HRF from 1971 � 2014, 9 cities recorded a decrease while 2 cities remained relatively unchanged with time while 25, 9 and 3 cities out of the 37 cities showed positive, negative and unchanged trends respectively in the occurrence of extreme rainfall (ERF) events. Generally, the average frequency of occurrence of HRF and ERF showed double peaksover the south in July and September in both cases, but with the highest peak occurring in September and July in the case of HRF and ERF respectively, though northern cities showed single peaks in August in both cases of HRF and ERF. However, spatial analyses showed that the HRF and ERF threshold values were observed to be decreasing with latitude as we move from south to north, which is in line with the spatial distribution of moisture across Nigeria. Having determined the effective threshold rainfall amount of heavy rainfall which is the main purpose of this study, now makes the heavy rainfall/flash flood risk forecast very subjective and location dependent. This implies that there is now increased efficiency in the forecast heavy rainfall. Furthermore, the result of this study engenders better planning for effective disaster risk management in Africa and in Nigeria in particular.

Keywords: Heavy Rainfall, Atmosphere, Threshold value, Forecasting, Extreme Rainfall

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