Rainfall parameters influencing erosivity in southeastern Nigeria

Abstract

Rainfall erosivity was characterized for the Guinea Savanna, Forest and Coastal belts of southeastern Nigeria (4° and 7°N; 6°30′ and 9°30′E). The highest maximum rainfall amounts ranged from 117 to 183 mm per rain event whereas the maximum 6-minute intensities ranged from 191 mm h −1 to 254 mm h −1 Advanced storms were dominant in the region. The values of the Kowal and Kassam kinetic energy equation (designated E k were 1.6 times higher than the values obtained using Wischmeier and Smith's equation (designated E). Compound rainfall erosivity used were the EI 30, KE ≥ 25mm h −1, AI m, E k I 30 and E k E m. The mean annual erosivity values using the EI 30 index ranged from 12,814 to 18,611 MJ · mm/ha · h. The KE ⩾ 25mm h −1 ranged from 141 to 249 MJ ha −1, the AI m from 849 to 1421 cm 2 h −1, the E k I 30 from 16,697 to 29,610 MJ · mm/ha · h and E k I m from 32,752 to 62,238 MJ · mm/ha · h. Rainfall erosivity approximations from rainfall amounts using indices from Roose and Arnoldus may be converted to Sl units (Foster et al.) by multiplying by a factor of 17. Rainfall erosivity differences were more pronounced between the Guinea Savanna and Forest or Coastal belts than between the Forest and Coastal belts. Erosivity is higher in the Forest or Coastal belts than the Guinea Savanna belt. The high erosivity of rains in southeastern Nigeria can be attributed to heavy storms of comparatively high intensities and, often, long duration. The magnitude of rainfall erosivity provides a useful insight into the causes of the catastrophic erosion problems in southeastern Nigeria.