As it was mentioned earlier, the 360-month period is not present in the periodogram of monthly total rainfall for the station of Kuwait International Airport during the time from January 1965 to December 2009, although http://www.selleckchem.com/products/Tipifarnib(R115777).html it was considered in the process to estimate the model parameters. If this period had been excluded from the model, then the rainfall pattern would have changed as shown in Figure 4(c). Obviously, the model in this case becomes insufficient to capture the large scale of the data pattern. The overall model error here becomes MAE = 13.2mm, which is about 4.7% larger than before. Accordingly, it can be assumed that the spikes shown in Figure 4(a) such as those for months 35, 135, 339, 376, 396, 470, and 518 that have not been simulated sufficiently by the model may result from hidden periods that had not been taken into account.

The implication is that the difficulty in fitting rainfall models by this criterion would require a wide range of historical data sufficient to show all possible periods responsible for the variable pattern.5. ConclusionsThis study examined the spatial and temporal variability of monthly total rainfall data obtained from weather stations located in the urban areas of Kuwait. It has been shown that a point estimate of rainfall can be considered spatially representative over the urban areas as the weather stations are sufficiently close in distance. This finding has been proved useful to model rainfall variability over the urban areas using a single dataset obtained from Kuwait International Airport for the time from January 1965 to December 2009.

A sinusoidal model has been proposed by considering a number of periods of 6, 12, 18, 20, 26, 30, 42, and 360 months. Except for the last one, all the periods have been identified in the rainfall data of Kuwait International Airport using the periodogram technique. The absence of the last period, which is due to insufficient length of time of data, reveals the role of hidden periods on model accuracy. This is confirmed by plotting the correlogram of the standardized residuals for the remaining stochastic component of the model, which exhibits the Entinostat signature of a repetitive oscillating movement due to the presence of other periods that have not been taken into account. A wider range of rainfall data would thus be necessary to develop a more accurate periodic model. Acknowledgment The author is grateful to the Directorate of Civil Aviation of Kuwait for providing the rainfall data used in this study.
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