Precipitation Concentration Impact on Flood frequency, Periodicities and Return Periods in Kaduna River

This study investigated precipitation concentration impact on flood frequency, periodicities and return periods in River Kaduna, North central Nigeria. Rainfall data within the catchment and discharge data for the river Kaduna were collected from Kaduna Meteorological Agency and department of Geography, Ahmadu Bello University, Zaria. The records collected for hydrological analysis span from 1962 to 2015. Preliminary statistical analysis such as correlogram, Box-Ljung Q statistics, Mann-Kendal test, Spearman’s Rho test etc, were used to check for outliers or error within data collected. Pearson type III was used for the prediction of expected discharge while annual and wet Precipitation Concentration Index (PCI) was calculated using the rainfall indicator equations. The preliminary results revealed normality in the data and rainfall increase causes a corresponding increase in discharge (correlation coefficient (r) value of 0.889 and determinant (r2) of 0.790), a relationship which suggests that increasing seasonal rainfall amount which linked to climate change has implications for flood generation, frequency and return periods. The above relationship is further buttressed following the relationship between exceedance probability and annual precipitation was defined by the linear regression y=0.002x+4.323 with the coefficient of determination R2 = 0.967. The high coefficient of determination shows a strong relationship between exceedance probability and precipitation. The seasonal PCI also show 8 years (15%) of Uniform Precipitation Distribution and 46 years (85%) of Moderate Precipitation Distribution. The discharge computed for the corresponding return periods ranged from 21,312 m3/s to 30,738 m3/s for return periods of 2 and 200 years. Rainfall amounts and variability are determinants of flood discharge characteristics such as onset of discharge, peak, recession, discharge variability etc, all of which can be influenced by climate change. Predicting flood from rainfall amounts and PCI are fundamental for designing hydrological response to rainfall fluctuation. Findings from this study are helpful when designing the catchment's flood mitigation system and water resources infrastructure to meet water supply needs of communities around the study area. The use of PCI yielded good results and in the absent of recent and consistent stream discharge data for most river basins in Nigeria can serve as an alternative approach for flood prediction in the country.