The Four-Parameter Kappa Distribution in Prediction of Standardized Precipitation Index

Document Type : Research Paper


1 Professor, Faculty of Civil Engineering, University of Tabriz, Iran

2 Ph.D. Student, Faculty of Civil Engineering, University of Tabriz, Iran


The standardized precipitation index (SPI) is
used vastly for drought monitoring. Among the many of drought indices, the
using of SPI for drought events in various time scales is more important. The
calculation is based on
fitting a
probability distribution that describes an
observed series of precipitation. There are many models for obtaining
probability distribution and parameter estimation, but choosing an appropriate
approach is important. This paper employs the four-parameter kappa distribution
and techniques of parameters estimation for calculation of SPI. The parameters
of kappa distribution are estimated by the genetic algorithm and method of
maximum likelihood, and finally the results indicate that the genetic algorithm
is more satisfactory for parameters estimation and SPI prediction.