FIGURE 2. Water table data from 11 observation wells vs rainfall rate every month
The flowchart of this study can be seen in Figure 3. The coefficient of skewness can be derived from the statistical tools in GIS. Based on the coefficient of skewness, the original data from each well is transformed using logarithmic transformation. The purpose of the logarithmic transformation is to gain a better coefficient of skewness and to stabilize the variance. The limit of the excellent coefficient of skewness is ±2 (Rubin, 2012), therefore if it is outside the threshold, the data is highly skewed, and logarithmic of transformation must be considered. In this case, the original data is within the range ±2; however, by the log-transformation, it is slightly improved. Therefore, it has been decided to use the log-transformation for better predictions.