Concerning the various effects of climate change on intensifying extreme
weather phenomena all around the world, studying its possible
consequences in the following years has attracted the attention of
researchers. As the drought characteristics identified by drought
indices are highly significant in investigating the possible future
drought, the Copula function is employed in many studies. In this study,
the two- and three-variable Copula functions were employed for
calculating the return period of drought events for the historical, the
near future, and the far future periods. The results of considering the
two- and three-variable Copula functions were separately compared with
the results of the calculated Due to the high correlation between
drought characteristics, bivariate and trivariate of Copula functions
were applied to evaluate the return periods of the drought. The most
severe historical drought was selected as the benchmark, and the drought
zoning map for the GCM models was drawn. The results showed that severe
droughts can be experienced, especially in the upper area of the basin
where the primary water resource is located. Also, the nature of the
drought duration plays a decisive role in the results of calculating the
return periods of drought events.