**Geography of Udi Cuesta Contribution to Hydro-Meteorological Pattern of the South Eastern Nigeria Meteorological Pattern of the South Eastern Nigeria**

**Geography of Udi Cuesta Contribution to Hydro-**

DOI: 10.5772/intechopen.72867

Ngene Ben Uchechukwu, Jonah C. Agunwamba, Imokhai T. Tenebe and Gideon O. Bamigboye Imokhai T. Tenebe and Gideon O. Bamigboye Additional information is available at the end of the chapter

Ngene Ben Uchechukwu, Jonah C. Agunwamba,

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.72867

#### **Abstract**

The presence of cuesta with escarpment plays an important role in the distribution of rainfall. Its role was studied and was put together in this work. Various parameters were studied and they include: amount of rainfall, elevation, latitude and the distance from the sea. In this research, frequency analysis was performed on the parameters and the log-pearson type III was considered the most suitable distribution method. Also, principal component analysis was used to determine that two components best estimates the variables with close correlation to be rainfall, elevation, latitude and distance from the sea as component 1 and distance to nearest neighbour and longitude as component 2. With regional coefficient of variation of 22%, the area has low variability which is an indication of high rainfall values with good consistency. Annual average rainfall of South Eastern Nigeria is at 1744 mm with bi-modal double peaks in July and September as in most parts of Southern Nigeria. High rain bearing wind speed of the area with escarpment obviously affect the rainfall pattern. From the determination of the difference in mean of rainfall, it is again obvious that areas close to Udi escarpment of the cuesta have difference in mean below or slightly above mean, hence indicating the effect on rainfall.

**Keywords:** distance from the sea, distribution method, elevation, latitude, rainfall and escarpment

## **1. Introduction**

The Udi escarpment of the South Eastern Nigeria is a long cliff or steep slope that separates an area of high elevation from an area of lower elevation as shown in **Figure 1** below. How this phenomenon affect rainfall pattern of the area and the water resources management is

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

meteorology, but on reaching the ground it is known to be element of hydrology. The region under study, south east Nigeria, is not known to have snow, hence the precipitation under discussion is limited to rainfall. Precipitation is the result of the cooling down of moisture containing air mass sufficiently to cause condensation to take place. The condensation is observed

Geography of Udi Cuesta Contribution to Hydro-Meteorological Pattern of the South Eastern…

http://dx.doi.org/10.5772/intechopen.72867

95

Though adiabatic cooling of air mass is the cause of condensation and rainfall, it takes the vertical transport pf the air mass for the cooling to take place. The type of precipitation and the intensity will depend on the nature of the movement of the moisturized air mass in a given area and it is seen in the following forms: convection, orographic, cyclonic and thunderstorm.

**i.** Convective precipitation: This type of precipitation results from heating of the earth's surface. It is characterized by summer thunderstorm and the warm air is lifted up to be displaced by a cooler air above it with the release of latent heat of vapourization. At a higher altitude the vapourized water droplets become frozen and hail forms or are intermixed with rainfall [7]. Convection precipitations are known to cause high intensity short

**ii.** Orographic precipitation: This type of rainfall takes place when an air mass rises over a mountain range. This occurs where the mechanical lifting of moist horizontal air mass occur over a natural barrier such as the Udi Cuesta. Since the area is close to the Niger Delta or the Nigeria coast, hot moist air mass moving horizontally will be lifted at the Cuesta. This will therefore cause rainfall in the windward slopes and lighter rainfall in the leeward slopes. A careful examination of **Figures 5**–**7** will confirm that the areas around the windward slope of the escarpment have a higher rainfall value than the leeward zone of Udi escarpment. This arises because the great source of air mass that causes rainfall is generated from the Niger Delta or coast of Nigeria moving northward as seen in **Figure 1**.

**iii.** Cyclonic precipitation: Cyclonic precipitation is associated with the movement of air masses from regions of high–pressure to low-pressure. The high and low–pressure regions are created by unequal heating of the earth's surface. Cyclonic precipitation may be

**iv.** Thunderstorms: Effect of thunderstorms which are usually very intense rainfall in nature is used when considering the sizing of urban drainage works. Thunderstorms often are

This is done with the aid of a rain gauge which may be recording or non-recording. The recording rain gauge is the automatic rain gauge which may be classified into three types (i) tipping bucket rain gauge (ii) weighing bucket rain gauge and (iii) syphon rain gauge. The non-recording rain gauge on the other hand is an ensemble and the rain to be measured is collected poured into a measuring cylinder which gives the value of the rainfall in millimeter of rain. Other methods used in obtaining rainfall measurement include weather radar, auto-

localized in nature but are associated with surface heating orographic effect.

to take place in the presence of condensation nuclei that is present in the atmosphere.

*1.1.1. Types of precipitation*

duration rainfall over a large area.

classified as either frontal or non-frontal cyclones.

matic weather stations, weather sensors and weather satellite [6].

*1.1.2. Measurement of precipitation*

**Figure 1.** Map of Nigeria showing zonal arrangement of areas of similar wind pattern.

the subject of this study. While the South Western Nigeria have a fair number of research on topography and water resources management, the South Eastern part have limited works in this regard, hence this work is needful.

Balogun [1] reported that areas of high rainfall also have low coefficient of variation and vice versa, this is the case for area around Udi. Areas around the range of Udi Plateau which runs perpendicular to the coastline of Nigeria have low coefficient of variation of rainfall. The importance of the variability study is seen in agriculture were there could be longer periods of rainfall absence thereby affecting plants and planting and also in hydrology, where drought is experienced and other human activities is affected.

Analysis of rainfall in general, enhances the management of water resources applications as well as the effective utilization of water resources [2]. Hydraulic Engineering designs such as dam height, embankment height, design discharge etc. are determined using results of frequency analysis. Specific areas such as the dimensioning of dams require the knowledge of frequency analysis and variability of annual rainfall to be efficiently carried out.

Even more compelling to the study of variability of rainfall data is the effect of climate change and global warming on water resources projects [3, 4]. This research has decided to look into the spatial and temporal variation of the area understudy. It also employed the use of frequency and principal component analysis to examine and interpret the collected data in the chosen areas [5].

## **1.1. Precipitation**

Precipitation defines the term used to describe the moisture coming out of the cloud and falling on the ground [6]. Precipitation just before it falls to the ground is governed by physics of meteorology, but on reaching the ground it is known to be element of hydrology. The region under study, south east Nigeria, is not known to have snow, hence the precipitation under discussion is limited to rainfall. Precipitation is the result of the cooling down of moisture containing air mass sufficiently to cause condensation to take place. The condensation is observed to take place in the presence of condensation nuclei that is present in the atmosphere.

#### *1.1.1. Types of precipitation*

the subject of this study. While the South Western Nigeria have a fair number of research on topography and water resources management, the South Eastern part have limited works in

Balogun [1] reported that areas of high rainfall also have low coefficient of variation and vice versa, this is the case for area around Udi. Areas around the range of Udi Plateau which runs perpendicular to the coastline of Nigeria have low coefficient of variation of rainfall. The importance of the variability study is seen in agriculture were there could be longer periods of rainfall absence thereby affecting plants and planting and also in hydrology, where drought

Analysis of rainfall in general, enhances the management of water resources applications as well as the effective utilization of water resources [2]. Hydraulic Engineering designs such as dam height, embankment height, design discharge etc. are determined using results of frequency analysis. Specific areas such as the dimensioning of dams require the knowledge of

Even more compelling to the study of variability of rainfall data is the effect of climate change and global warming on water resources projects [3, 4]. This research has decided to look into the spatial and temporal variation of the area understudy. It also employed the use of frequency and principal component analysis to examine and interpret the collected data in the chosen areas [5].

Precipitation defines the term used to describe the moisture coming out of the cloud and falling on the ground [6]. Precipitation just before it falls to the ground is governed by physics of

frequency analysis and variability of annual rainfall to be efficiently carried out.

this regard, hence this work is needful.

94 Engineering and Mathematical Topics in Rainfall

**1.1. Precipitation**

is experienced and other human activities is affected.

**Figure 1.** Map of Nigeria showing zonal arrangement of areas of similar wind pattern.

Though adiabatic cooling of air mass is the cause of condensation and rainfall, it takes the vertical transport pf the air mass for the cooling to take place. The type of precipitation and the intensity will depend on the nature of the movement of the moisturized air mass in a given area and it is seen in the following forms: convection, orographic, cyclonic and thunderstorm.


#### *1.1.2. Measurement of precipitation*

This is done with the aid of a rain gauge which may be recording or non-recording. The recording rain gauge is the automatic rain gauge which may be classified into three types (i) tipping bucket rain gauge (ii) weighing bucket rain gauge and (iii) syphon rain gauge. The non-recording rain gauge on the other hand is an ensemble and the rain to be measured is collected poured into a measuring cylinder which gives the value of the rainfall in millimeter of rain. Other methods used in obtaining rainfall measurement include weather radar, automatic weather stations, weather sensors and weather satellite [6].

#### *1.1.3. Mean rainfall estimation for a watershed*

Several methods are employed in calculating the mean rainfall value of a catchment which is useful for many hydrologic investigations. The methods include arithmetic mean, the Theissen polygon, the isohyetal method, application of mathematical surface fitting techniques, finite element method and two-axis technique [8]. The arithmetic mean, Thiessen polygon and isohyetal methods are explained in the following example. The annual rainfall in three locations of Nsukka (A), Enugu (B), Ezzamgbo (C) and Ishiagu (D) is shown in **Table 1** and **Figure 2** as 1517 mm, 1609 mm, 1468 mm and 1799 mm respectively.

**1.2. Wind**

Winds are one of the main factors that affect the climate of a place. It is therefore important to have a good knowledge of the climatic factors that affect the movement of air mass or wind. A critical element in the process of generation of rainfall of any type is wind or movement of air which is also useful as a source of energy generation. Generally, air mass or wind can be harnessed for the supply electricity where they are in abundance such as the case in many locations in Nigeria as shown in **Table 1**. From the principal component analysis tables, it is shown that there exist a strong correlation between rainfall and distance from the sea which is the source of rain bearing moist air mass. Sea and land breeze is experience in the coastal area in Nigeria, which is close to the southeast. During the day, land area is heated more than the sea, thereby causing air over land to expand and rise, causing low-pressure areas on land. This causes cooler air from sea to move inland toward the low-pressure area on land resulting in light wind known as sea breeze. At night the reverse process is experienced where the land

Geography of Udi Cuesta Contribution to Hydro-Meteorological Pattern of the South Eastern…

http://dx.doi.org/10.5772/intechopen.72867

97

The air mass in Nigeria oscillates between North and South in harmony with the movement of the thermal equator and it is influenced by land mass and water bodies [9]. Nigeria has two types of wind movement in a year, also known as the North Western trade wind and a harbinger of harmattan season and the South Eastern trade wind, which bring the rainy season. The South Western wind (June/July) is a result of the dominance of the tropical maritime air mass from the south atlantic which causes the rainy season. During the period (December/January),

cool more rapidly than the sea resulting in land breeze.

**Table 1.** Classification of wind power density according to location in Nigeria.

*1.2.1. Types of pressure and air mass (wind)*

The average mean rainfall for the area may be calculated as follows:

(a) Arithmetic mean method:

#### (1517 + 1609 + 1468 + 1799)/4 = 6393/4 = 1598 mm

(b) Thiessen polygon method:


#### (c) Isohyetal method:


From the calculations using the three methods, the Isohyetal method has the lowest weighted average precipitation value and hence may be chosen depending on the overall objective of the hydrologic investigation.

## **1.2. Wind**

*1.1.3. Mean rainfall estimation for a watershed*

96 Engineering and Mathematical Topics in Rainfall

(a) Arithmetic mean method:

(b) Thiessen polygon method:

\*As a fraction of total area sum = 1571.7 mm

(c) Isohyetal method:

the hydrologic investigation.

\*As a fraction of total area Sum = 1486 mm

1517 mm, 1609 mm, 1468 mm and 1799 mm respectively.

(1517 + 1609 + 1468 + 1799)/4 = 6393/4 = 1598 mm

The average mean rainfall for the area may be calculated as follows:

**Mean Depth Area between Isohyetal\* weighted depth (mm)**

**STN Depth (mm) Area of polygon\* weighted depth (mm)**

A 1517 0.23 348.9 B 1609 0.35 563.2 C 1468 0.29 425.7 D 1799 0.13 233.9

1200 0.06 72 1300 0.13 169 1400 0.21 294 1500 0.26 390 1600 0.20 320 1700 0.11 187 1800 0.03 54

Several methods are employed in calculating the mean rainfall value of a catchment which is useful for many hydrologic investigations. The methods include arithmetic mean, the Theissen polygon, the isohyetal method, application of mathematical surface fitting techniques, finite element method and two-axis technique [8]. The arithmetic mean, Thiessen polygon and isohyetal methods are explained in the following example. The annual rainfall in three locations of Nsukka (A), Enugu (B), Ezzamgbo (C) and Ishiagu (D) is shown in **Table 1** and **Figure 2** as

From the calculations using the three methods, the Isohyetal method has the lowest weighted average precipitation value and hence may be chosen depending on the overall objective of Winds are one of the main factors that affect the climate of a place. It is therefore important to have a good knowledge of the climatic factors that affect the movement of air mass or wind. A critical element in the process of generation of rainfall of any type is wind or movement of air which is also useful as a source of energy generation. Generally, air mass or wind can be harnessed for the supply electricity where they are in abundance such as the case in many locations in Nigeria as shown in **Table 1**. From the principal component analysis tables, it is shown that there exist a strong correlation between rainfall and distance from the sea which is the source of rain bearing moist air mass. Sea and land breeze is experience in the coastal area in Nigeria, which is close to the southeast. During the day, land area is heated more than the sea, thereby causing air over land to expand and rise, causing low-pressure areas on land. This causes cooler air from sea to move inland toward the low-pressure area on land resulting in light wind known as sea breeze. At night the reverse process is experienced where the land cool more rapidly than the sea resulting in land breeze.

#### *1.2.1. Types of pressure and air mass (wind)*

The air mass in Nigeria oscillates between North and South in harmony with the movement of the thermal equator and it is influenced by land mass and water bodies [9]. Nigeria has two types of wind movement in a year, also known as the North Western trade wind and a harbinger of harmattan season and the South Eastern trade wind, which bring the rainy season.

The South Western wind (June/July) is a result of the dominance of the tropical maritime air mass from the south atlantic which causes the rainy season. During the period (December/January),


**Table 1.** Classification of wind power density according to location in Nigeria.

described as air mass in motion and it is one of the climate parameters according to [12]. This motion is caused by pressure differences across the earth's surface due to the uneven heating of the earth by solar radiation [13] Energy for electricity and other uses in some part of Africa has been on the decline, and its demand has been on the increase irrespective of this fact. This fact aforementioned has prompted the supreme council of energy in Egypt to come up with a blue print geared towards improving/or improvising other potential and viable energy sources in the electricity sector thereby cutting down on dependents on fossil fuels [14] and to some scholars, wind is a viable option. Nigeria is growing rapidly with estimated population of over 140 million [15] and will shoot up undoubtedly in the coming years. This will adversely affect the need for more energy and this call for concern. In a quest to cushion the effects of human wants, lot of natural resources is required with most of these resources used for this purpose are not sustainable. Unfortunately, the daily activities of humans are hugely dependent on the natural resources available and their longevity somewhat proportionate to sustainable practice [16].

Geography of Udi Cuesta Contribution to Hydro-Meteorological Pattern of the South Eastern…

http://dx.doi.org/10.5772/intechopen.72867

99

In Nigeria, as well as obtained elsewhere, it is necessary to determine the amount of air mass

**iii.** Evaluation of productivity and cost effectiveness of a particular wind energy system

**iv.** Determine operational requirements such as resource information, load management,

Previous attempts aimed at determining the characteristics of wind energy in Nigeria have been insufficient as they are regional in nature. Such efforts in literature include the works of [17–21]. The work is aimed at determining the country wide character variation of Nigeria wind both in terms of location and time. It involves determining the shape and scale factors of various sites and hence the wind power densities will be ascertained to enable classification of sites in terms of their wind densities. Furthermore, the coefficient of variation of different sites is determined including the relationship it has with wind speed. Both the relationship between wind speed, altitude, the monthly and annual variation are computed for the various zones viz.: Coastal, Inland, Middle Belt and the Far-Northern region of Nigeria. The various characteristics of wind mentioned above gives an insight to the productivity of a turbine generator; hence, the need for proper location for their optimal and efficient utilization in electricity generation is required [19]. According to [22], sites with average wind speed of 7.5 m/s in Europe will generate wind power up to 250 KW. Using this criterion alone will limit the number of stations for possible wind turbine generators in Nigeria, hence further analysis to point out other areas of possible siting of such systems. This research also uses wind speed data from the Nigeria Meteorological Agency to determine available wind resources for each of the 24 stations in the Network. It further shows the zoning effects of the stations and how the area of same physical and climatic conditions affect wind speed and wind power density. The **Figure 1** below indicates the zonal arrangement of wind speed in Nigeria with South East

in motion to enable:

**i.** Proper design of Civil Engineering Structures. **ii.** Planning for siting of wind turbines/generators

procedure and prediction of maintenance or system life.

based on available wind resources.

falling under the Inland region.

**Figure 2.** Map of Nigeria showing Udi escarpment and the two river basins [9].

the wind system shifts down from the tropic of Capricorn with the Sahara becoming the high pressure zone. This brings about the dry and cold wind – the tropical continental air mass with a northeasterly wind with low pressure belt in the south. At this time, the inter-tropical front will be in southern coastal fringes of Nigeria.

#### *1.2.2. Characteristics and uses of Nigeria wind energy*

Wind speed noted Back and Bretherton [10] explains a moderate amount of daily viability in precipitation. According to their study, faster winds are related to high incidence of rainfall which also explains daily rainfall variability. As earlier noted there exist three main types of air mass lifting which include frontal lifting, orographic lifting and convective lifting and they are functions of the type of atmospheric circulation and local conditions, geography and wind included [11].

This work therefore looked at the influence of wind on the rainfall pattern of the south east Nigeria and the energy generating capacity of the wind available in the country. Wind is described as air mass in motion and it is one of the climate parameters according to [12]. This motion is caused by pressure differences across the earth's surface due to the uneven heating of the earth by solar radiation [13] Energy for electricity and other uses in some part of Africa has been on the decline, and its demand has been on the increase irrespective of this fact. This fact aforementioned has prompted the supreme council of energy in Egypt to come up with a blue print geared towards improving/or improvising other potential and viable energy sources in the electricity sector thereby cutting down on dependents on fossil fuels [14] and to some scholars, wind is a viable option. Nigeria is growing rapidly with estimated population of over 140 million [15] and will shoot up undoubtedly in the coming years. This will adversely affect the need for more energy and this call for concern. In a quest to cushion the effects of human wants, lot of natural resources is required with most of these resources used for this purpose are not sustainable. Unfortunately, the daily activities of humans are hugely dependent on the natural resources available and their longevity somewhat proportionate to sustainable practice [16].

In Nigeria, as well as obtained elsewhere, it is necessary to determine the amount of air mass in motion to enable:


the wind system shifts down from the tropic of Capricorn with the Sahara becoming the high pressure zone. This brings about the dry and cold wind – the tropical continental air mass with a northeasterly wind with low pressure belt in the south. At this time, the inter-tropical front will

Wind speed noted Back and Bretherton [10] explains a moderate amount of daily viability in precipitation. According to their study, faster winds are related to high incidence of rainfall which also explains daily rainfall variability. As earlier noted there exist three main types of air mass lifting which include frontal lifting, orographic lifting and convective lifting and they are functions of the type of atmospheric circulation and local conditions, geography and wind included [11]. This work therefore looked at the influence of wind on the rainfall pattern of the south east Nigeria and the energy generating capacity of the wind available in the country. Wind is

be in southern coastal fringes of Nigeria.

98 Engineering and Mathematical Topics in Rainfall

*1.2.2. Characteristics and uses of Nigeria wind energy*

**Figure 2.** Map of Nigeria showing Udi escarpment and the two river basins [9].


Previous attempts aimed at determining the characteristics of wind energy in Nigeria have been insufficient as they are regional in nature. Such efforts in literature include the works of [17–21]. The work is aimed at determining the country wide character variation of Nigeria wind both in terms of location and time. It involves determining the shape and scale factors of various sites and hence the wind power densities will be ascertained to enable classification of sites in terms of their wind densities. Furthermore, the coefficient of variation of different sites is determined including the relationship it has with wind speed. Both the relationship between wind speed, altitude, the monthly and annual variation are computed for the various zones viz.: Coastal, Inland, Middle Belt and the Far-Northern region of Nigeria. The various characteristics of wind mentioned above gives an insight to the productivity of a turbine generator; hence, the need for proper location for their optimal and efficient utilization in electricity generation is required [19]. According to [22], sites with average wind speed of 7.5 m/s in Europe will generate wind power up to 250 KW. Using this criterion alone will limit the number of stations for possible wind turbine generators in Nigeria, hence further analysis to point out other areas of possible siting of such systems. This research also uses wind speed data from the Nigeria Meteorological Agency to determine available wind resources for each of the 24 stations in the Network. It further shows the zoning effects of the stations and how the area of same physical and climatic conditions affect wind speed and wind power density. The **Figure 1** below indicates the zonal arrangement of wind speed in Nigeria with South East falling under the Inland region.
