Uncertainty analysis of SPI and SRI calculation using bootstrap in the Mediterranean regions of Algeria

The standardized precipitation index (SPI) and the standardized runoff index (SRI) are widely used in drought monitoring. In the calculation of these indices, the time scale and distribution functions are especially significant. In the current study, the uncertainty in the estimation of the two indices, in terms of time scale and distribution functions, was investigated in the wadi Mina basin (Algeria) using monthly precipitation and runoff values based on the gamma-II (GAM-II), extreme value-III (EVD-III), Pierson-III (PEI-III) and Weibull-II (WEI-II) distribution functions. With this aim, precipitation and runoff amounts were calculated considering 12- and a 24-month time scales; then, using the bootstrap method, 1000 random sample were generated for each precipitation and runoff event and for each time scale, and the confidence interval of the two indices was calculated at around 95