**2. The study area**

The study site is the South Eastern Zone of Nigeria. This region falls within the latitude 6' N and 8' N and longitude 4′ 30′E and 7′30'E also described as the inland region of the country according to **Figure 1**. Udi escarpment divides the zone into two area viz. South Eastern scarplands under Anambra /Imo River Basin and Eastern borderlands under Cross River Basins and the apex of Udi plateau at 300 m above sea level. The whole region which is densely populated covers an area of about 40,000 sq. km and represent 4% of the country's land mass with the physical environment and climate described in the **Figure 2** below.

#### **2.1. Physical environment**

The site is of the lowland region of southern Nigeria, which drains to the Atlantic Ocean through the Anambra/Imo River Basin and the Cross River Basin. According to [9], the geology of the area is basically of the stratified sedimentary rock of secondary to tertiary geological era. The unroofing of the anticlines left the Udi escarpment and brought about the undulating Cross River Basin right of the scarpland.

#### **2.2. Climate and hydrology of study area**

The South Eastern Nigeria is of the wet tropical type climate with mean annual temperature in the range of between 27° C and 34° C. The temperature of the area as observed by [9] is highest around March–April when the overhead Sun passes through Nigeria latitude. The rainfall, however, of the area has an annual average of 1744 mm, which is decreasing inland from the Niger Delta area or the coast of Nigeria .This is quite clear in **Figure 3** below. The Annual rainfall regime of the area is of the double maxima with double peak in July and September and an August break period. The high rainfall between May–September has a lowering effect on temperature of the area.

**3. Materials and methods**

**Figure 3.** Contour map of South Eastern Nigeria rainfall.

**3.1. Measure of reliability**

(a) Mean

is tested for reliability and consistency before use.

The data for this study area is the secondary data of 12 stations with monthly rainfall within the south eastern Nigeria obtained from the Nigeria Meteorological Agency, Lagos, Federal College of Agriculture, Ishiagu, Ebonyi State., Nigeria [23]. The data used is tabulated as shown in **Table 2** below. This table shows the location, annual rainfall amount, latitude, longitude elevation and period of data collection. For some areas however, it is necessary to observe that the data was for period less than 10 years owing to the absence of sufficient data. However, even with missing data as observed from the table below, the information obtained

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From the annual mean calculation of each station and the region, a departure from average is determined and plotted to indicate how mean rainfall for each stations differ from the mean.

This helps us to determine the variability experienced in the rainfall distribution.

The climate of Nigeria is classified into Rainy (April – October) and Dry (November – March) seasons, with each of the seasons lasting approximately six months. Annual rainfall ranges from 500 m in the extreme north to 3000 m along the coast. Nigeria is governed by high pressure southwest monsoon wind from the Atlantic in June–July pushing the inter-tropical front to the Sahara (northern) region of the country [1, 9]. At this point the sun is around the tropic of cancer or close to it, hence high temperature (25 ° C south and 40 ° C north) and low pressure. In December–January, on the other hand, the sun is at the tropic of Capricorn causing the wind system to shift to the south. At this time, the Sahara region becomes the high pressure belt forcing dry and cold wind to blow northeasterly to the low pressure area of the south. The wind system usually arrive the country about September and gradually spread throughout the country and last until March when the sun repeats the processes again. This process represents the wet and dry seasons of Nigeria of which the South East is a part. The **Table 1** represents the wind power available in various locations within the country. The area of the South East with the escarpment has maximum wind power of 122 w/m<sup>2</sup> , altitude of 167 m and is classified as class 2 as shown in **Table 1** below. Classification indicates class 1 for the weakest location for siting of wind power generators to class 7 the strongest possible site for electric energy generator site.

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**Figure 3.** Contour map of South Eastern Nigeria rainfall.
