Inadequacy of the gamma distribution to calculate the Standardized Precipitation Index

Revista Brasileira de Engenharia Agrícola e Ambiental

Meschiatti, Monica C.¹  Blain, Gabriel C.¹ 

[1] Instituto Agronômico, Campinas, Brazil

关键词: rainfall departures;    normality test;    goodness-of-fit tests;   

DOI  :  10.1590/1807-1929/agriambi.v19n12p1129-1135

学科分类：农业科学（综合）

来源: Universidade Federal de Campina Grande * Centro de Ciencias e Tecnologia

【 摘 要 】

The Standardized Precipitation Index was developed as a probability-based index able to monitor rainfall deficit in a standardized or normalized way. Thus, the performance of this drought index is affected by the use of a distribution that does not provide an appropriate fit for the rainfall data. The goal of this study was to evaluate the adjustment of the gamma distribution for the rainfall amounts summed over several time scales (Pelotas, Rio Grande do Sul, Brazil), to assess the goodness-of-fit of alternative distributions to these rainfall series and to evaluate the normality assumption of the Standardized Precipitation Index series calculated from several distributions. Based on the Lilliefors test and on a normality test, it is verified that the gamma distribution is not suitable for calculating this Index in several timescales. The generalized normal distribution presented the best performance among all analysed distributions. It was also concluded that the drought early warning systems and the academic studies should re-evaluate the use of the gamma distribution in the Standardized Precipitation Index calculation algorithm. A computational code that allows calculating this drought index based on the generalized normal distribution has also been provided.

【 授权许可】

Unknown