Determining the Effect of Intensity and Duration of Drought on the Lag Time Between Meteorological and Hydrological Drought and Examining Uncertainties (Case Study: Anzali Basin)

There is a deficiency in the number and depth of researches regarding the significant association between meteorological and hydrological droughts, and investigating the effects of uncertainties in the lag time between the two phases of the droughts. In this study, the lag time between the two phases of meteorological and hydrological droughts was investigated based on the available observations, using frequency-counting methods for the Anzali wetland basin with 9 meteorological and 20 hydrometric stations having recorded data from 1985 to 2015. Due to the fact that in the 30-year observation period, the possibility of severe droughts is low, to generate unobserved meteorological drought conditions of varying magnitude, continuity, and intensity, using the Monte Carlo method artificial rainfall was simulated. The SWAT water balance model was employed to generate the hydrological drought situations for different meteorological drought scenarios. The effect of the persistence and severity of meteorological drought on the lag time was investigated using the statistical technique of cross-correlation matrices. The results showed that an increase in meteorological drought duration increases the hydrological drought duration while an increase in the drought intensity reduces the lag time between the two phases of the droughts. The confidence interval of the lag time between meteorological and hydrological droughts showed that there is a chance of 70% to have a lag time of one month or less between the two phases of the droughts.