A time series is a set of observations, each of which is recorded at a specific time. the objective of analysis time series are- Forecasting, Control, understanding feature of the data including seasonality, cycle, trend and its nature, description and explanation (Hamilton, J. D. ,2020). ) The annual rainfall series are plotted in figure 2, where its varies widely, with the lowest annual total recorded (50 mm) in 1987, while the highest total was (297 mm) in 2013.the Median of rainfall (108 mm) so 25% of them about (82 mm) and 75% about (153 mm).
Analysis of the monthly average of troposphere column ozone
In this paper we used the linear and exponential statistical method, to detect the trend in long-term rainfall data series. A trend exists when there is a long-term decrease or increase in the data. General linear or most often nonlinear (damped and exponential) component that changes over time. (Mudelsee, M., 2019).
Two methods of trend taken in this study liner trend, as show in figure.3 and exponential trend in figure.4, the trend( red line) in both methods is decrease with time. MAPT and MAD in exponential lees than in liner because that’s mean the accuracy of exponential is the best .also MSD in exponential higher than liner Because outliers have an effect on it. The forecast of annual rainfall for next four years after 2018 made (green line) where in 2022 the amounts of it will be (150 mm ) in liner method but will be (125 mm) in exponential method.
The Simple Moving Average (SMA) method was discovered by G. U. Yule in 1909. The process of computing moving averages smoothens out the fluctuations in the time series data. It 7 can be shown that if the trend is linear and the oscillatory variations are regular (Rahardja, D. ,2020).
the average of a span of series values surrounding and including the current value. The span is the number of series values used to compute the average. If the span is even, the moving average is computed by averaging each pair of uncensored means. The number of cases with the system-missing value at the beginning and at the end of the series for a span of n is equal to n/2 for even span values and (n–1)/2 for odd span values. (Koutrasetal.,2020).
The 5 moving average (red line) in figure 5 show that rain still variation so we take second 5 moving average to know the liner trend (red line) as show in figure 6. the trend shows that rainfall decrease and in 2020 will be (138 mm)