TIME SERIES ANALYSIS OF ANNUAL RAINFALL IN NIGERIA (A CASE STUDY OF THE SIX GEO-POLITICAL ZONES) 1985-2016
Rainfall is a determinant factors of many human and natural resources, hence the need to study the trends is highly Paramount. This project examines the recent trends in the rainfall pattern in Nigeria ( a case study of the six political zone in Nigeria from 1985 to 2016) using the data from the central bank of Nigeria statistical bulletin. The purpose of this study is to examine the pattern of trend and seasonal component that constitute the annual amount of rainfall, To forecast annual amount of rainfall in Nigeria using the best fitted model and having a descriptives analysis of the annual data collected as part of the preliminary investigation.
The jarque-bera statistics, mean, minimum and maximum amount of rainfall was used for the descriptives analysis. Time plot was used to study the pattern of rainfall based on each of the political zone over the years under study,Time series analysis of annual rainfall values are used to illustrate the trend of rainfall and also used in estimating seasonal variation. least square model was used in trend line analysis and to forecast for the subsequent years.
The result shows that rainfall is higher in southern region while in northern region rainfall is very low and moderate in the western region. The ordinary least square result shows that the model is statistical siginifant judging from the six geo-political zones, knowing the pattern and trend of rainfall in Nigeria, the distribution across each geo-political zones shows that may, June, July, August and September have higher rainfall than other months. In North -Central, North-East, Middle-Belt shows a seasonal pattern while South-East, South-West and South-South shows a cyclic pattern. 1988 has the highest volume of rainfall over the years.
TABLE OF CONTENT
List of Tables
List of Figures
TABLE OF CONTENT
1.1 INTRODUCTION 1
1.2. STATEMENT OF THE STUDY 7
1.3. AIM AND OBJECTIVES OF THE STUDY.
1.4 SIGNIFICANCE OF THE STUDY
1.5. SCOPE OF THE STUDY
1.6. SOURCES OF DATA
1.7. LIMITATION OF THE STUDY
1.8. DEFINITION OF TERMS
2.2 TIME SERIES ANALYSIS
2.2.1. TYPES OF TIME SERIES
2.2.2 USES OF TIME SERIES
2.3 RAINFALL TREND
2.4 MEASUREMENT OF RAINFALL
2.5. RAINFALL INTENSITY
2.6. EFFECT OF RAINFALL ON AGRICULTURE
2.7 TYPES OF RAINFALL
2.8. APPLICATION OF TIME SERIES TO RAINFALL PATTERN
3.2. POPULATION, SAMPLE SIZE, SAMPLING TECHNIQUES
3.2.2 SAMPLE SIZE
3.2.3 MODEL ESTIMATION TECHNIQUES
3.2.4 CHARACTERISTICS OF TIME SERIES
3.3 TIME PLOT
3.4 ORDINARY LEAST SQUARE
3.5 SEASONAL VARIATION
3.5.1 AUTOCORRELATION PLOT
3.5.2. SEASONAL INDEX
4.2. DESCRIPTIVE STATISTICS OF RAINFALL PATTERN IN NIGERIA
TABLE 4.2 DESCRIPTIVE RESULT
4.3. TIME PLOT FOR EACH GEO POLITICAL ZONE DISTRIBUTION OF RAINFALL
4.4. ORDINARY LEAST SQUARE
TABLE 4.4 ORDINARY LEAST SQUARE RESULT
4.5.1. AUTOCORRELATION PLOT
4.6. SEASONAL INDEX
5.1. SUMMARY OF FINDINGS
- BACKGROUND OF THE STUDY
Rain is liquid water in form of droplets that have condensed from atmospheric water vapor and then precipitated that is, become heavy enough to fall under gravity (Mordurch, 1995, Sala and Lauenroth, 1982). Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. It provides suitable conditions for many types of ecosystems, as well as water for hydroelectric power plants and crop irrigation. Rainfall is a determinant factor of many natural occurrences.
Rainfall is very crucial for the economic development of a country, three main characteristics of rainfall are amount, frequency, and intensity. Precise knowledge of these three main characteristics is essential for planning its full utilization. Rainfall is very crucial for the economic development of Nigeria as the integral percentage of the people get involved in rain fed agriculture. A state whose economy is heavily dependent on productive rain fed agriculture. Rainfall trends are often cited as one of the causes of socio-economic problems such as food insecurity. Long term records of daily rainfall have been compiled for years, norm and standard deviations have been worked out, floods and drought have been defined and climate zones of potential evaporation less precipitation have been mapped from rainfall pattern and crop studies. It has been cited that Living organism cannot survive without optimum water supply (Oladipo, 1993). Although it has been argued that rainfall and temperature are the most important climatic determinants of crop survival and production especially in Nigeria. Apart from the socio-economic problems facing Nigeria farmers, climatic variability constitutes a major limiting factor in crop production due to the practice of rain-fed agriculture. Due to changes in the characteristic of rainfall occasioned by global warming which has led to rainfall variability uncertainties at the onset, duration, total annual amount of rainfall, intensity and its general or favorable distribution cross the growing season month (Audu 2006).The water forecasting is a very powerful decision supporting, the precise estimation of the future water consumption. It is essential for determining the water management policy including the efficient water use and water purchase (Ejike).
Rainfall trend is the significant change in the spatial and temporal patterns of rainfall. Rainfall trend in other words can be said to be the general tendency, movement, or direction and pattern in which rainfall takes. In the global scene for example, rainfall trend analyses, on different spatial and temporal scales, has been of great concern during the past century because of the attention given to global climate change from the scientific community, they indicate a small positive global trend, even though large areas are instead characterized by negative trends (IPCC, 1996). Murphy and Timbal (2007) reported that most of the rainfall decline (61%) has occurred in autumn (March–May) in southeastern Australia. A similar rainfall decline occurred in the southwest of Western Australia around 1970 that has many common features with the southeastern Australia decline. However, in the regional level Nicholson (2000) observed that one of the most important contrasts in rainfall is the multi-decade persistence of anomalies over northern Africa. Rainfall variability on the other hand is the degree to which rainfall amounts vary across an area or through time. Variability of rainfall can be used to characterize the climate of a region. Rainfall in Nigeria is subjected to wide variability both in time and space. This variability has assumed a more pronounced dimension as a result of climate change. According to Chidozie et al, rainfall variability increases from the northwest to the southwest, while between-year (yearly) rainfall variability increases from the north central to the southeast. This study further confirms that rainfall variability over time follows a spatial trend within ascertain arbitrary boundary (Laux et al, 2010, Mudita et al, 2008). The major cause of rain production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts. If enough moisture and upward motion is present, precipitation falls from convective clouds (those with strong upward vertical motion) such as cumulonimbus (thunder clouds) which can organize into narrow rain bands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation which forces moist air to condense and fall out as rainfall along the sides of the mountains. On the leeward side of mountains, desert climate can exist due to the dry air caused by down slope flow which causes heating and drying of the air mass. The movement of the monsoon trough or inter-tropical convergence zone, brings rainy seasons to savannah climes (Laux et al, 2010, Mudita et al 2008). The urban heat island effect leads to increased rainfall, both in amounts and intensity, downwind of cities. Global warming is also causing changes in the precipitation pattern globally, including whether conditions across Eastern North America and drier conditions in the Tropic Rainfall characteristics in Nigeria have been examined for dominant trend notably by Olaniran (1990, 1992) and Olaniran and summer (1989, 1990). They showed that there has been a progressive early retreat of rainfall over the whole country, and consistent with this pattern, they reported a significant decline of rainfall frequency in September and October which, respectively coincide with the end of the rainy season in the northern and central parts of the country. The pattern of rainfall in northern Nigeria very high in spatial and temporal dimensions with inter-annual variability of between 15 and 20% (Oladipo,1993). As a result of the large inter-annual variability of rainfall, it often results in climate hazards, especially floods and severe and droughts with their devastating effect is on food production and associated calamities and sufferings(Oladipo, 1993,Okorie 2003, Adejuwon 2004).Rainfall is one of the key climatic resources of Nigeria. Crops and animals derived their water resources largely from rainfall. It is considered as the main determinant of the types of crops that can be grown in the area and also the period of cultivation of such crops and the farming systems that can be practiced. Nigeria’s population and economic development are linked to climate sensitive activities including rainfall. An understanding of current and historical rainfall trends and variation is inevitable to the country’s future economic and tourism development. Rainfall is the most important natural factor that goes a long way in determining a lot of things especially agricultural production in Nigeria, especially in the southern part of Nigeria. The changes and variability associated with rainfall and the pattern of extreme high or low precipitation are very important for agriculture as well as the economic development of the state. It is a well-known fact that the pattern of rainfall is changing on both the global and the regional scales due to global warming (Hulme et al, 1998, Kayano, 2008). As the moves to encourage the agricultural sector in other to avoid food scarcity continues to gain ground and acceptability, information on rainfall variability is of essence for the design of water supply and supplemental agricultural irrigation schemes and the evaluation of alternative cropping and of soil water management plans. Much as long rainfall records are mostly available in many countries, little use is made of this information because of the unpredicted nature of the records. (Minaand Sayedul, 2012). It is important to state that rainfall of Nigeria and West Africa in generally is influenced by the dynamics of continental air mass and maritime air mass which meet along a slanting surface called Inter-Tropical Discontinuity (ITD) (Odekunle, 2004).
1.2 STATEMENT OF THE PROBLEM
Water resources are essential renewable resources that are the basis for existence and development of a society. The agricultural sector in Nigeria today has been characterized by low productivity over the years, because one of the key factor that determine a good productivity is rainfall which is very pertinent for the economic growth and development of Nigeria at large because the greater percentage of the people (especially adults) actively participate in rain fed agricultural practices (crop production, animal husbandry and plantation). As a country whose economy largely depends on efficient and productive rain-fed agriculture, rainfall patterns and trends are often quoted as one of the major causes of several socio-economic problems like food insecurity in the state.
Previous studies by Olaniran (2000) have analyzed rainfall trends in Nigeria, also Olaniran and Summer (2003) shows that there has been a progressive early retreat of rainfall over the whole country, and consistent with this pattern, they reported a significant decline of rainfall frequency in September and October, respectively which coincide with the end of the rainy season in the northern and central parts of the country.
Subyan (2004) worked on the Geo statistical pattern of annual and seasonal mean rainfall patterns in southwest Saudi Arabia. The difference of mean annual rainfall over West and Central Africa because of the severity of drought was confirmed by Ragab and Prudhomme (2002). Their findings and results showed that long-term trend of rainfall series over these regions depict major climatic discontinuity.
Rainfall variability in Africa has been studied by several researchers since the inception of recent drought period in the 70’s. Many studies compared Sahelian rainfall with rainfall over West and Central African sub-regions (Ogo&Adeyemi 2009, Gbuyiro et al, 2002).
Enete & Ebenebe (2009) showed that the trend suggested a general decline in rainfall values in recent times. Rainfall values for the years under study suggested values between 265.37mm and 320.21mm. Rainfall characteristics in Nigeria have been studied for dominant trend notably by Olaniran & Summer (1989, 1990). They found that there was a progressive early decline of rainfall over the country. Following the pattern, they reported a noticeable and significant decline of rainfall frequency in September and October which coincide with the end of rainy season in almost every parts of the country especially in the Northern and Central parts but not all have been able to capture the rainfall trend over all the state in Nigeria but concentrating on one or more state in their studies. In view of this, the study will examine the pattern of trend and seasonal component that constitute the amount of rainfall in Nigeria and also to forecast for the subsequent years.
1.3 Aim AND OBJECTIVES OF THE STUDY
The aim of the study is to examine the application of time series analysis on annual rainfall in Nigeria.
Having understood that rainfall is important in the development of the nation and state wealth, also in the life of people living in that nation. The objectives of this work are to:
- have a descriptive analysis of the annual data collected as part of the preliminary investigation.
- determining the pattern of trend and the seasonal component that constitute annual amount of rainfall in Nigeria.
- to forecast Annual amount of rainfall in Nigeria using the best fitted model for subsequent years
1.4 SIGNIFICANCE OF STUDY
Climate change and global warming has increased at an alarming rate as a result of anthropogenic factors such as urbanization. Therefore, this study is relevant because it will assist researchers to understand the future consequences of rainfall variation due to climate change. This is because climate change has been linked to the climate, which in turn would affect where and how people make a living, how the flora and fauna species would thrive, how food would be produced which would be influenced by availability of water.
Studies has shown that both plant and animal require a specific amount of water for their existence, excess or inadequate supply of water could lead to their demise. Carbon dioxide is emitted into the atmosphere at an accelerated rate and also the depletion of the ozone layer which has caused the earth’s surface to be heated up.
This study would also be of help to tourists in planning the time of their visits. This study would equally be of help to the policy makers in Nigeria, agriculturists and researchers who are interested in the rainfall pattern of the Country.
1.5 SCOPE OF THE STUDY
This research work is culled from the Central Bank Statistical Bulletin for the period of 31 years (1985-2016) and the research work will be limited to Nigeria data using the six Geo –Political Zones.
1.6 Sources of Data
Central Bank of Nigeria Statistical Bulletin:
This is where Central Bank of Nigeria(CBN) publishes all the monetary values of different activities of sectors in the country, CBN published the data yearly in order for researchers, government, student, policy maker among others that used it as analytical technique in policy making, decision making, budget implementation and making research by student on yearly basis.
1.7 LIMITATION OF THE STUDY
This study intends to expand its research tentacles to the global economy in terms of model application and literature review, but limit the scope of the analysis to the Nigerian economy. The study seeks to analyze the trend series analysis of annual rainfall in Nigeria. It is therefore pertinent to state that the cluster of this study will not go beyond the confines of the Nigerian economy in data usage only. In order to fully capture the subject matter in terms of analysis, a thorough secondary quantitative analysis will be conducted with data covering a period of 31 years (1985 to 2016) due to non-availability of some important data and the high cost of collecting data from source, but nevertheless the study was done in the best way to achieve its objectives to make recommendations and conclusion.
1.8 DEFINITION OF TERMS
RAINFALL: The amount of rain that falls in a location over aperiod of time.
AGRICULTURE: The science, art or practice of cultivating soil, raising crops, feeding, breeding and raising livestock.
TIME SERIES: is simply a sequence of numbers collected at regular intervals over a period of time.
CLIMATE: The general weather condition of a region, as temperature, air pressure, humidity, precipitation, sunshine, cloudiness and winds thorough the year, averaged over a series of years.
TREND: A pattern of gradual change in a condition or an averaged tendency in a time series.
DROUGHT: A period of dry weather, especially a long one that is injurious to crops.
ANOMALY: Deviation from the normal or from the expectation
SEASON: A period of the year during which a particular activity usually takes places in the human world or among plants and animals e.g rainy and dry season.
TEMPORAL VARIATION: This means changes that occurred in the distribution of a particular event.
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