A Time Series Analysis of the Monthly Distribution of Rainfall in Enugu Metropolis

A Time Series Analysis of the Monthly Distribution of Rainfall in Enugu Metropolis

ABSTRACT

It is widely accepted that water supply will be a pressing issue in this century. Thus, the position of adequate rainfall in the development of human and natural resources is worthwhile to research work. The data used in this project work was the monthly amount of rainfall in Enugu city within the period of (2000- 2012). A preliminary inspection of the data revealed that the data has no trend but consist of multiplicative seasonal movements. Furthermore, the monthly data was also found to be stationary and serially uncorrelated by the Augmented Dickey-Fuller test of unit root and the Autocorrelation test for serial correlation of the error term respectively.

The exponential smoothing procedures were adopted for the construction of the best fit model for the prediction of future rainfall patterns in Enugu. This was achieved by algorithms aimed at smoothing out all irregular components inherent in the series. The best fit model parameters were used to predict monthly rainfall distribution for 2013. The result suggested heavy rainfall in general for the year in question with its amplitude in October.

CHAPTER ONE

INTRODUCTION

1.1 Background to the study

Rainfall is a determinant factor of many natural occurrences. Vegetation distribution and types over land masses are a result of rainfall. Animals breeding periods synchronize with the rainfall period. Rainfall events have been directly linked to sickness and diseases particularly those of waterborne and vector-borne types. Crop planting, yields and harvest are influenced by rainfall. Investments in agricultural produce and products are expected to be done by the knowledge of rainfall and other weather conditions.

Naturally, rainfall variability is of spatial and temporal forms and within these variations, if by time series analysis no significant trend is obtained then the rainfall is steady, otherwise, it has changed Janhabi and Ramakar(2013).

With regards to rainfall, studies have pointed to the fact that the climate is changing (Goswami et al, 2006). Specifically, the research of (Ragab and Prudhomme, 2002) discusses the variability and uncertainty of rainfall across the whole globe amidst global warming and among others, it states that while North Africa witnesses rainfall decrease, the regime of rainfall in some parts of South Africa is increasing. On the other hand, no coherent trend has been recorded in some other regions, in the face of different significant trends of other regions in Sri Lanka (Jayawardene et al, 2005). However, (Odjugo, 2010) argues that not any change in the climate should be considered as climate change since climate fluctuates. And in his overview of climate change in Nigeria, he established that rainfall has decreased by 81mm within 105 years period. Thus, not to mistake climate fluctuation for climate change (Nsikanet al, 2011).

The growth of population demands increased domestic water supplies and at the same time results in higher consumption of water due to expansion in agriculture and industry. Mismanagement and lack of knowledge about existing water resources and changing climatic conditions have consequences of an imbalance of supply and demand of water. The problem is pronounced in semi-arid and arid areas where these resources are limited.

Generally, the study of weather and climatic elements of a region is vital for the sustainable development of agriculture and planning. Particularly, rainfall and temperature temporal analyses for trends, fluctuations and periodicities are deemed necessary as such can indirectly furnish with the “health” status of an environment. (Afangidehet al, 2010).

Before the modelling of the rainfall forecast, preliminary statistical tests were carried out on the time series to test the presence of trend and stationarity in it. Simple linear regression analysis may provide a primary indication of the presence of trends in the time-series data. The Box-Jenkins method is a univariate time series analysis. It is thus essential to analyse the presence of the unit root in the time series. The stationarity of the time series can be tested with the Augmented Dickey-Fuller Test. This test is popularly used to check the presence of unit root in the time series (Mahalakshmiet al, 2014).

The Nigerian climate is humid in the south with annual rainfall over 2000mm and semi-arid in the north with annual rainfall less than 600mm. Generally speaking, three climatic zones cover the North, middle and southern areas of the country: Sahel, Savanna and the Guinea zones. Rainfall commences in approximately March/April in the southern coastal zones, spread through the middle zone in May/June and reaches the northern zone in June/July, reaching its peak over middle and northern zones between July and September (Babatundeet al, 2011). The negative impact of climate change such as temperature rise, erratic rainfall, sand storms, desertification, low agricultural yield, drying up of water bodies and sea-level rise are real in the desert prone eleven front-line states of Nigeria. Environmental degradation and the attendant desertification are major threats to the livelihood of the inhabitants of the front-line states of Nigeria. These lead to increasing population pressures, intensive agricultural land use, overgrazing, bush burning, etc (Oluwafemiet al, 2010).

1.2 Statement of the Research Problem

Rainfall is one of the key climatic elements of Enugu, because crops, animals and indeed humans derive 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 practised. In previous findings, the coefficients of rainfall only approximate annual average values but does not express vividly the deviation from the long term average either up or down the normal curve. Whereas, each “up and down” fluctuation can lead to conditions which are warmer or colder, wetter or drier. For instance, while individual monthly total rainfall in an annual rainfall series may look stable in terms of runoff within the city, the deviations from the long term mean might show continuous increases with runoff and discharges overwhelming the drains which were designed to cope with normal rainfall in the area.

Invariably, with further significant variations in the rainfall characteristics of the area, scientific studies must be undertaken to provide society with accurate information on the real and potential impacts of extreme climatic variability, as well as, the mitigation and adaptation options available. At this time when the world is grappling with diverse environmental problems including global warming, ozone depletion, acid rain, killer hurricanes, destructive thunderstorms, droughts and major flood episodes, efforts at finding explanations to these problems should be of great importance since the environmental, social and economic cost of managing extreme climatic variability is bound to be enormous from the standpoint of society and policymakers (Ekpoh, 2011).

1.3 Aim and Objectives of the Study

The aim of the study is on time series analysis of the monthly rainfall distribution in the Enugu metropolis and trends as an imperative for human adaptation to climate change in the area. The specific objectives are as follows;

To examine monthly rainfall anomalies of Enugu for the period 2000 – 2013 To examine the trend in the monthly rainfall anomalies for Enugu using the same 2000- 2013 monthly rainfall data. To assess the monthly rainfall probability in the area using the 2000-2013 rainfall data. To make recommendations towards adapting to the implications of rainfall anomalies in Enugu.
1.4 Scope of the study

This research is restricted to the city of Enugu. The analysis is restricted to the period of (2000-2013) rainfall data drawn from archives of NIMET Enugu. This rainfall climatology study of Enugu involved the analysis and determination of the series, averages, deviation from averages, extremities, probability assessment as well as relationships.

1.5 Relevance of the study

This research will attempt to identify episodes of rainfall inconsistencies and expose the trend in rainfall behaviour in the area. It will help us understand the likely causes of an extreme event such as flood in the area. It will also help in ascertaining the vulnerability of the inhabitants of the area to rainfall variability.

Furthermore, possible adaptations to the problem of rainfall extremities shall be proffered as it may help in cushioning the continuous calamities caused by climate change in the area. The study will also enhance runoff discharge prediction and the design of drains and buildings in the area, as it will afford us the opportunity of predicting mean rainfall values as well as the likely impact on building and drainage channels in the area.

The study will also furnish the political class/leaders, administrators and policymakers with facts that will guide them in the formulation of policies towards adapting to the problems of climate change in the area. It is hoped that this research work will serve as a reference work for future studies as well as an understanding of climatic variability in the area and Enugu state in general.