Development of Erosivity Map for Nigeria

摘要

Mean monthly rainfall data, computed from monthly rainfall data, spanningabout a period of 36 years, were used to compute rainfall erosivity indices for someselected stations in Nigeria. About 38 locations were selected, cutting across all of thefive (5) agro-ecological zones of Nigeria. The Fournier index C, defined as ‘C = P12/P’where P1 is the rainfall amount in the wettest month of the year and P is the annualrainfall amount, was used. Values of rainfall erosivity indices ranged from 26.0mm atYandev in the southeastern part of Nigeria to106.7mm at Yelwa in the northwestern partof the country.The indices were used to develop a rainfall erosivity map for Nigeria using ArcView GIS3.2a (ESRI 2000). The map reveals that Nigeria may be broadly divided into five (5)major erosion risk zones. The southwestern part is generally in the low erosion risk zone,with the exception of the coastal portion of Lagos, Ondo, Edo and Delta states. Thesoutheast and central portions are generally in the moderate to severe erosion risk zone,while the extreme northwest and northeastern part are in the severe to extremely severerisk zone.