**4. Influence of climate**

The rainfall of southern Nigeria generally is heavy and aggressive. Rainfall amount ranges from over 2500 mm in the southernmost region towards the Atlantic Ocean to about 1500 mm annu‐ ally around River Benue in the northern borders. Rainfall intensities are high and often above 50 mm/h with short interval intensities in excess of 100 mm/h. Rainfall often come between the month of March and last till October. In some years the rainy period is unduly prolonged while in other years their onset may be delayed for more than 5 weeks. The present global climate change resulting from El-Niño and has not helped issues in this regard.

The nature of the rainfall regime contributes significantly to the erosivity of rainfall. Rainfall erosivity is the potential ability of rain to cause erosion. It is also a function of the physical characteristics of rainfall. Obi and Salako [11] reported that the raindrop sizes obtained gen‐ erally in the Guinea savannah ecological zone of West Africa ranged from 0.6 to 3.4 mm. The mean drop sizes (D50) of 28 rainfall events ranged from 1-1 to 2.9 mm. There are experimen‐ tal evidence to suggest that intensity and energy are likely to be closely linked with erosivi‐ ty. A number of statistical relations have been established in the past between the erosive power and amount of rainfall in other parts of the tropical region [12, 13, 10, 14]. The best estimator of soil loss was found to be a compound parameter, the product of the kinetic en‐ ergy of the storm and intensity. In Nigeria, the total kinetic energy load of 1091 mm rainfall at Samaru in Northern Nigeria was about 3600 Jm-2. This was twice the amount recorded in southern Africa by Stocking [15]. However, the product of the kinetic energy of the storm and the maximum intensity of the rainfall during the first 30 mins of a storm (EI30) was most significantly correlated with soil loss determined on standard field plots [16]. Erosivity val‐ ues therefore have been used successfully to produce iso-erodent map of West Africa [14].

In southeastern Nigeria, Obi and Ngwu [17] characterised the rainfall regime and recom‐ mended Lal's index of Aim as having advantage over other indices of erosivity such as KE> 1 and EI30. However, Salako et al. [18] compared all the available indices of erosivity adopt‐ ed in southeastern Nigeria and came up with some modifications of existing ones. Two indi‐ ces EkI30 and EkIm were recommended

Where;

sis and location of this particular gully site on the landscape is similar to numerous other

The rainfall of southern Nigeria generally is heavy and aggressive. Rainfall amount ranges from over 2500 mm in the southernmost region towards the Atlantic Ocean to about 1500 mm annu‐ ally around River Benue in the northern borders. Rainfall intensities are high and often above 50 mm/h with short interval intensities in excess of 100 mm/h. Rainfall often come between the month of March and last till October. In some years the rainy period is unduly prolonged while in other years their onset may be delayed for more than 5 weeks. The present global climate

The nature of the rainfall regime contributes significantly to the erosivity of rainfall. Rainfall erosivity is the potential ability of rain to cause erosion. It is also a function of the physical characteristics of rainfall. Obi and Salako [11] reported that the raindrop sizes obtained gen‐ erally in the Guinea savannah ecological zone of West Africa ranged from 0.6 to 3.4 mm. The mean drop sizes (D50) of 28 rainfall events ranged from 1-1 to 2.9 mm. There are experimen‐ tal evidence to suggest that intensity and energy are likely to be closely linked with erosivi‐ ty. A number of statistical relations have been established in the past between the erosive power and amount of rainfall in other parts of the tropical region [12, 13, 10, 14]. The best estimator of soil loss was found to be a compound parameter, the product of the kinetic en‐ ergy of the storm and intensity. In Nigeria, the total kinetic energy load of 1091 mm rainfall

change resulting from El-Niño and has not helped issues in this regard.

gully sites in the region.

160 Research on Soil Erosion Soil Erosion

**Figure 2.** Typical gully site

**4. Influence of climate**

Ek is in MJha-1 (kinetic energy)

I30 is 30 minutes rainfall intensity and

Im being maximum intensity computed over a 6 minutes duration

Rainfall therefore plays very significant roles in the erosion hazard of southeastern Nigeria. The rainfall distribution, amount and intensity in combination of other environmental fac‐ tors contribute in accelerating the rate of interrill rill and gully erosion in southeastern Ni‐ geria. This is evidenced in the sense that as rainfall amount decrease northwards, the rate of all types of soil erosion by water decreases.
