Abstract

GUTIERREZ-LOPEZ, Alfonso; VARGAS-BAECHELER, José; RESENDIZ-TORRES, Víctor  and  CRUZ-PAZ, Ivonne. Simplified Desing of a Drought Index, Using a Mixed Probability Function. Tecnol. cienc. agua [online]. 2016, vol.7, n.5, pp.135-149. ISSN 2007-2422.

Nowadays, there are many procedures to characterize the phenomenon of drought; most of them are based on the Standardized Precipitation Index (SPI), which is calculated based on historical records of rainfall for a certain period of study. This set of data is standardized using various probability distributions, which enables the analysis of the impacts of droughts at different time scales. The complexity of this process is the use of various probability distributions and that none of its parameters have a physical meaning. This paper presents a simplified methodology for calculating the SPI, based on the hypothesis that a series of events occur randomly in time. A Poisson process is used to explain the number of raining days and an exponential distribution to characterize the mean rainfall high. Looking for a physical explanation of the parameters of the distribution of mixed probability (Poisson-exponential), they correlate directly with the SPI index, obtaining a modified index is calculated simply by counting the number of raining days in the period; representing a simple and trustworthy way the condition of drought. The methodology is applied in eight northern states of the Mexican Republic.

Keywords : Drought; Poisson distribution; rainfall regimen; standardized precipitation index.

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