APPLICATION OF STATISTICAL FUNCTIONS FOR RAINFALL DISTRIBUTION MODELLING AND SPI CALCULATION IN MEDITERRANEAN WATERSHED

Abstract

Drought indices are one of the most widely used methods for drought monitoring because of their ease of application and interpretation.The most commonly used drought index method is the Standardized Precipitation Index (SPI) method, which uses precipitation as an input.The performance of the Standardized Precipitation Index (SPI) is affected by the choice of an incorrect probability distribution function, which can distort index values, exaggerating or minimizing drought severity.This study aims to test the suitability of the statistical distribution functions proposed by the Bootstrap model, which estimates the closest probability distribution for calculating the SPI at time scales (TS) of 3, 6, 9, and 12 months.Daily rainfall data collected at the Dar Chaoui meteorological station were used for the period 2000-2021.Distribution function parameters were estimated using the maximum likelihood (ML) method and the Kolmogorov-Smirnov method and then confirmed using the Bootstrap method.The results show several extremely dry picks, especially in the 9-and 12-month time scales.