M. Bagheri-Bodaghabadi
Abstract
The Importance of Correcting Land Indices in Determining Land Suitability Classes Introduction: Land evaluation plays a decisive role in determining land suitability for the intended uses. For this purpose, various approaches have been proposed, among which the parametric approach has a special place. ...
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The Importance of Correcting Land Indices in Determining Land Suitability Classes Introduction: Land evaluation plays a decisive role in determining land suitability for the intended uses. For this purpose, various approaches have been proposed, among which the parametric approach has a special place. In this approach, the land indices (LIs) are calculated using the Khidir method (the square root) and/or the storrie method, and then the land suitability classes are determined based on the LIs. Unfortunately, in many land suitability studies, the land index has been used without being corrected, called uncorrected land index. This has led to many differences in the results of different approaches of land suitability evaluation. The current study shows the importance of employment of the corrected land index and its effect on land suitability classes. Materials and Methods: In this study land suitability classes were determined by the four methods including 1-simple limitation, 2- number and intensity of limitations, 3- Kiddir (square root) and 4- storrie, using the two cases i.e. the corrected land index and the uncorrected land index. Properties and criteria for determining land suitability classes are shown in Table1. Simple limitation method is based on the Liebig’s law or the law of the minimum. Land classes are defined according to the lowest class level of the land characteristics. Number and intensity of limitations method has been described in table 1. In parametric approach land index (uncorrected land index) is calculated using Kiddir and Storrie methods as shown in equations 1and 2, respectively. The relationships between uncorrected land indices and corrected land indices are presented in table 2. (1) (2) Then, a simulation process was done for the eight characteristics involved in calculating the land suitability index. For this purpose, one million random values were created for each of the S1 to N2 classes; so that the minimum rating (Rmin) was a random number for each class in own defined range (Rating in Table 1) and the other seven characteristics were random numbers between Rmin and 100. For example, in the S2 class, a minimum random number is in the range of 60 to 85 and seven other characteristics were between this Rmin and 100. Finally, a total of five million random simulations were created. Results and Discussion: Table 3 shows the results of five million simulations for S1 to N2 classes. Based on the minimum, maximum and mean values obtained, it can be seen that the simulation process is acceptable. These numbers show that the simulations have simulated almost all the cases that may occur in reality, from the best to the worst. Based on the results, it is clear that the mean values of the land indices for the Storrie method are much lower than the Khiddir ones, but the mean values for the corrected land indices, do not differ too much, in the both the Storrie and Khiddir methods. These results are sufficient to conclude the importance of using the corrected land indices and to show the difference between the results obtained from the corrected land indices and the uncorrected land indices. Tables 4 to 8 show the results of one million simulations for each suitability class. The results showed that using the corrected land indices, the results of the four employed methods are much closer, especially for the Storrie and Khiddir methods. All together, the simple limitation method was more consistent with the Khiddir method. On the other hand, the employed methods differed greatly when the uncorrected land indices were used. The analysis of five million simulations has shown that the contradictory results of land evaluation methods in various studies can be quite logical, mathematically, but with a different probability. Totally, the results of the uncorrected land indices may be largely inaccurate and misleading, and may show unrealistic results. Therefore, it is strongly suggested that the corrected land indices be used in determining the suitability classes, and then the results be compared with the observations in the reality. Conclusions: According to the findings of the current study, it can be illustrated that it is very important and necessary using the corrected land index to determine the land suitability class. The study showed, using the corrected land index leads to the closeness of the results of different methods, so that there is no significant difference between Storrie and Khiddir methods. In general, the results of the Khidir method are closer to the simple constraint method than the Storrie ones, although using the uncorrected land index, there was a very significant difference between the Khiddir and Storrie methods, but using the corrected land index the difference was too small and insignificant.
