FIGURE 7 QQ pot of the RMSSE and the normal distribution values: (a) the period of November 2018 – July 2019 (weak spatial dependence), (b) the period of August 2019 - February 2020 (strong spatial dependence)
Cross-validation using correlation of coefficient and RMSE for each well was done to observe the variance of each well during November 2018 – July 2019 (weak spatial dependence), and August 2019 – February 2020 (strong spatial dependence) (Table 6). Most wells with strong spatial dependence have a high correlation of coefficient (0.76 – 0.97). On the other hand, most of the weak spatial dependence data have a relatively low positive correlation of coefficient (0.37 – 0.98), and even sometimes, it becomes negative like in well 13. The highest correlation happens in well 4, well 7, and well 8 with a coefficient 0.98, 0.95, and 0.96, respectively. It indicates that during the weak spatial dependence period, these three wells were influenced by the rainfall that occurred in January 2019.
TABLE 6 Correlation of coefficient and RMSE between observed and predicted WL for strong spatial dependence, weak spatial dependence, and all data compiled