Joint frequency analysis of rainfall and precipitation concentration index (PCI) at Birjand and Tabas meteorological stations, South Khorasan Province, Iran

Abstract

In this study, copula functions and precipitation concentration index were used for the joint frequency analysis of the conditional probability of rainfall-rainfall and PCI-PCI at Birjand and Tabas meteorological stations in eastern Iran. Monthly rainfall data in the statistical period 1969-2018 were considered in this regard. The results of PCI at the studied stations showed that at both stations the distribution of rainfall pattern is highly irregular, which was worse at Tabas meteorological station. By selecting the appropriate marginal distribution function and also confirming the correlation between rainfall- rainfall and PCI-PCI at Tabas and Birjand meteorological stations, the Gumbel-Hougaard and Clayton copulas were selected for the pair variables, respectively. The results of conditional probability showed that with different probabilities, rainfall and PCI of each station can be estimated using the rainfall and PCI of another station. For example, according to the presented curves, if the annual rainfall of Birjand meteorological station is 220 mm, with 80% probability, the annual rainfall of Tabas meteorological station will be about 110 mm. According to the presented curves and the use of copula functions in the joint analysis of the rainfall and rainfall pattern, it is possible to better water resources management and water harvesting in the region.