Analysis and Generalization of the Classification Equations of the Palmer Drought Severity Index. A. Theoretical Considerations

The Palmer Index reckons as a returning point in the evolution of the drought quantifying models, that in spite of passing four decades since the introduction, its special procedure and properties justifies its utilization. This index is usually addressed as a water budget accounting method for moisture anomaly estimation, yet its unique classified technique has been occasionally faced with brief indications and inaccurate deductions. Therefore, scrutinizing the analysis section of events intensity and duration throughout the drought severity index (PDSI) calculations (classified process) is essential for theoretical and operational purposes. This subject was taken into account in the present article for more practicality of the superior capabilities of the index. Accordingly, the results can be summarized at the following headings: 1) deriving the generalized structure of the classification equation, via introducing an innovated neutral intensity, 2) explaining its analytical extraction for both of the excess and lack of moisture, which is required to adjust the duration factors regionally, 3) identifying the effect of categorization on this factors and on the starting or ending event analysis, also providing an opportunity for new systematic suggestions about the classes, 4) describing the backtracking procedure that is fairly a complex part, as well as, making it applicable even for the other indices apart from the PDSI and 5) making preparation to improve proper handling of the procedure, and expanding its development and modification or improvement potential.