RAINFALL PARAMETERS INFLUENCING EROSIVITY IN SOUTHEASTERN NIGERIA

Rainfall erosivity was characterized for the Guinea Savanna, Forest an d Coastal belts of southeastern Nigeria (4 degrees and 7 degrees N; 6 degrees 30/ and 9 degrees 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 kineti c energy equation (designated E(k)) were 1.6 times higher than the val ues obtained using Wischmeier and Smith's equation (designated E). Com pound rainfall erosivity used were the EI(30), KE greater than or equa l to 25 mm h(-1), AI(m), E(k)I(30) and E(k)I(m). The mean annual erosi vity values using the EI(30) index ranged from 12,814 to 18,611 MJ . m m/ha . h. The KE greater than or equal to 25 mm 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 bullet> mm/ha . h. Rainfall erosivity approximations from rainfall amounts using indices from Roose and Arnoldus may be converted to SI u nits (Foster et al.) by multiplying by a factor of 17. Rainfall erosiv ity differences were more pronounced between the Guinea Savanna and Fo rest or Coastal belts than between the Forest and Coastal belts. Erosi vity is higher in the Forest or Coastal belts than the Guinea Savanna belt. The high erosivity of rains in southeastern Nigeria can be attri buted to heavy storms of comparatively high intensities and, often, lo ng duration. The magnitude of rainfall erosivity provides a useful ins ight into the causes of the catastrophic erosion problems in southeast ern Nigeria.