comparison of the impact of drought on surface and sub-surface water in the kaka-reza basin

Awareness of drought interrelationships and hydrological response of watersheds is a prerequisite for optimal management of surface and groundwater resources. the aim of the present study was to compare the impact of drought on surface and subsurface waters in the kaka-reza basin. in this study, after controlling the data, a common period (1982-2017) for hydrometric and rainfall stations was considered. then the standardized precipitation index (spi) and the standardized discharge index (sdi) were calculated for the 1-, 3-, 6-, 9-, 18-, 12- and 24-month time steps. the base flow and the corresponding index were calculated by b-flow lyne and hollick recursive digital filter. then, the standardized base flow index (sbfi) was calculated by adapting the spi method for the corresponding time steps. finally, the relationships between spi, sdi and sbfi were investigated and analyzed using correlation method. the results showed that the greatest effect of drought on groundwater for the 9- and 12-month time step with coefficient of determination 0.87, while the effect of drought on surface water for the corresponding time step has a coefficient of determination of about 0.4.