Chapter 1: Introduction1.1 Background of StudyRainfall is the fall of moisture from the sky to the earth surface in any physical form. It is the one of the most difficult elements to predict. The liquid precipitation and rain can be different intensity such as light rain or heavy rain. It is a measure of amount of rain that falls over time. Annual maximum rainfall is an extreme occasion with hazard duration for a river basin with instant effect to agriculture, soil conservation, drainage and so on. The knowledge of annual maximum rainfall is very important for flood mitigation and water resources management. Water is vital for any life process because any living things cannot survive without the water.
The main source of water in any area is rain. The yield of crops is depends on the rainfall pattern which makes it essential to measure the probability of occurrence of rainfall from past history of hydrological data using statistical analysis. Kelantan is Malaysia’s second largest agricultural production area. There is an increasing water use for economic and industrial developments. Monsoon season is the major raining season to Kelantan which often cause reaction of watershed during precipitation-runoff process. It can results in floods, landslides, debris disasters and so on.
An applicable probability distribution of the annual maximum rainfall is very important to reduce losses arising from these types of disasters. Rainfall analysis using probability distribution and annual maximum rainfall can enhance the management of water resources application as well as the effective usage of water resources. Those information from the analysis can be used to prevent floods and droughts, and applied to the planning and designing of water resources related engineering such as reservoir design, flood control work, drainage design, and soil and water conservation planning. In addition, the information also provide fundamental to the society to get ready for heavy rainfall events. Water resources planner, farmers and urban engineers require reliable data for the management and application of water resource strategies. Malaysia has experienced variability in rainfall for the past 10 years especially in Kelantan.
In this situation, it can expect to have increment in the frequency and concentration of extreme rainfall events. Thus, this will cause severe floods in state of Kelantan every year during the monsoon season. Flood can cause property damage and significant loss of life every year in Kelantan River Basin. Malaysia usually has two monsoon seasons such as Southwest and Northeast Monsoon. According to the weather forecast, there will be more rainfall in Northeast Monsoon where the Kelantan located in comparison to the Southwest Monsoon. Occurrence of flood in Kelantan seems to be a serious issue in the monsoon season.
Flooding due to massive rainfall not only cause damage to properties but also loss of life and serious agony to the victims. Flooding occurs when the river loses its ability to contain the water and the water overflows the river bed flood the low lying areas and adversely affecting the human settlements. 1.2 Problem StatementFloods happen annually in the east of Peninsular Malaysia and resulted in the damage to property, destruction of crops, loss of livestock and non-functioning of infrastructure facilities.
The flood in Kelantan area has become the most common natural hazard which bring a lot of harm for every time during the flood event. Citizen live in this affected area have to face with this kind of situation where they need to be evacuated and moves their private and belongings to the safe area. A change in climatic conditions stress living things by forcing their adaptation. The flood disaster is relevant to rainfall variability. There is a relationship between rainfall inputs and flood generation. Floods may be produced by high intensity of rainfall or longer duration of rainfall.
Monitoring the maximum rainfall data annually is extremely significant. This is because most of the human activity is influenced by climatic conditions. Heavy rainfall can lead to numerous hazards such as landslides can threaten human life, disrupt transport and communications and cause damage to buildings and infrastructure.
Therefore, more specific research like rainfall analysis is needed to overcome the problem in Kelantan. 1.3 Objectives of StudyThe objectives of this study are:1. To investigate the best fit probability distribution in describing the characteristics of annual maximum rainfall in a flood prone area, Kelantan River Basin.2. To determine best fit probability distribution of annual maximum rainfall in Kelantan by using different statistical analysis.
3. To determine the parameters of different probability distributions.4. To evaluate the performance of different probability distribution models based on three goodness of fit tests.5. To compare the performances of different probability distributions.
1.4 Scope of StudyThe main objective of the study is to find the best fit probability distribution and perform an analysis of annual maximum rainfall in Kelantan, Malaysia as this area had caused by heavy rainfall brought by the Northeast monsoon starting from November to March every year. Six rain gauge stations are provided having annual rainfall data over 20 years were selected to perform the rainfall frequency analysis. The daily rainfall data for a period of 20 years is used to understand normal rainfall, deficit rainfall and excess rainfall. The choice of an appropriate statistical analysis is one of the major problems in engineering practice. The selection of the best fit probability distribution is based on the highest total test scores acquired by summing up the scores of each goodness of fit test. A suitable probability distribution will provide accurate prediction of maximum rainfall for the particular year.
In this study, the five common probability distribution are used to estimate the rainfall frequency such as Beta, Gumbel, Generalized Extreme Value, Log- Pearson Type III and Weibull distribution. Probability distribution does relate the magnitude of the extreme events like floods with their number of occurrences such that their chance of occurrence with time can be predicted easily. The probability of occurrences of rainfall can be determined by fitting a probability distribution to the set of hydrological data.
The hydrological data is analysed and the variability in the data is studied from the statistical parameters in order to fit the distribution. Three goodness of fit tests like Kolmogorov Smirnov, Anderson Darling and Chi-Squared tests are used to evaluate the performances of different probability distribution as stated above.1.5 Significance of StudyThe significances of this study are as follows:1.
To contribute the research knowledge of describing the characteristics of annual maximum rainfall in a flood prone area, Kelantan River Basin.2. To assist and support the government to reduce the risk of flooding in Malaysia in the future.3. To provide insight into rainfall variability to help improve the range of climate prediction.
4. To develop a better probability distribution on the rainfall in a flood prone area which can be useful for the development of agriculture and increase the living standard of the citizen in the area.