Global Journal of Researches in Engineering, J: General Engineering, Volume 1 9 Issue 2

Figure 3: Correlation between annual erosivity index and average annual precipitation From figures 1 and 2, the month of August has the highest erosivity index. The months with zero rainfall had zero KE and zero EI. As the years go by, the relationship between precipitation pattern and erosivity index becomes more pronounced, i.e higher the precipitation, the higher the erosivity index. This is confirmed by the finding of review of rainfall erosivity in Brazil by Oliveira et al., (2002), that higher erosivity values observed in the tropics are caused by the high amount of precipitation, intensity, and KE of rain. Also that the ranges of rainfall erosivity values in tropical regions are similar and they are higher than those observed in other temperate climate regions. Figure 3 shows the correlation between annual erosivity index and average annual precipitation. The correlation between annual erosivity index and average annual precipitation was expressed as Y = 11.496x + 50.215. The coefficient of Determination R 2 of 0.651 (65.1 %) is an indication that precipitation alone contributed 65.1 % of erosion hazard during the period of study. The remaining percentage could be explained by soil, conservation, management and anthropogenic factors. The increase in precipitation could be as a result of climate change. III. C onclusion The rainfall erosivity factor (R) is one of the key factors in the USLE model and has gained increasing importance as the environmental effects of climate change have become more severe. The erosivity index for Auchi, was evaluated using Lombadi equation covering a period of 2005 – 2014. It was discovered that higher rainfall values resulted in high erosivity index values which was in line with other tropical climates. The average annual erosivity index for the city during the period of study was 587.32 MJ mm/hr. The R 2 of 0.651 shows that precipitation alone contributed 65.1% of the erosion risk within the study period. The knowledge of impact of rainfall on erosivity is essential in soil erosion risk assessment and for soil and water conservation planning. R eferences R éférences R eferencias 1. Angulo-Martínez M. and Beguería S. Estimating rainfall erosivity from daily precipitation records: a comparison among methods using data from the Ebro Basin (NE Spain). Journal of Hydrology 379 (1- 2): 111-121 (2009). 2. Isikwue M. O., Ocheme E. and Aho M. I. (2015). Evaluation of rainfall erosivity index for Abuja, Nigeria using Lombardi method. Nigerian Journal of Technology (NIJOTECH) Vol. 34 No. 1, January 2015, pp. 56 – 63. 3. Loureiro N. and Coutinho M. (2001). A New Procedure to Estimate the RUSLE EI 30 Index Based on Monthly Rainfall Data and Applied to the Algarve Region, Portugal”, Journal of Hydrology, Vol. 250: 2001, pp 12-18. 4. Morgan, C. (1979). Field and Laboratory Examination of Soil Erosion as a Function of Erosivity and Erodibility for Selected Hillslope Soils from Southern Ontario. PhD Thesis, University of Toronto. 1979, 114pp. 5. Morgan, R. P. C. (1942). Soil Erosion and Conservation. – 3rd ed. Blackwell publishing 6. Oliveira, P.T., Wendland, E. Nearing, M.A. “ Rainfall Erosivity in Brazil: A review” Catena Vol. 100, 2002, pp 139 – 147. 7. Onuoha S. N., F. I.Idike, Orakwe, L. C. (2012). Water Supply Resources for Domestic Purposes in Auchi metropolis of Edo State, Nigeria. International Journal of Engineering and Technology Volume 2 No. 6, June, 2012. 8. Silva, A.M. (2004). Rainfall Erosivity Map for Brazil. Catena.Vol. 57, 2004, pp 251–259. Wichmeier, W.H. Smith, D.D. Predicting Rainfall Losses—A Guide to Conservation Planning. USDA. y = 11.496x + 50.215 R² = 0.651 0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 0 .00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 Erosivity Index (MJ mm/hr) Average Annual Precipitation (mm) Global Journal of Researches in Engineering 38 Year 2019 © 2019 Global Journals Estimation of Rainfall Erosivity Index for Auchi, Edo State, Using Lombardi’s Method ( ) Volume XIxX Issue II Version I J