The Analysis of Relationship Between Meteorological and Hydrological Droughts In Atrak Watershed

Drought is a natural and recurring phenomenon which causes water scarcity in various sectors. In comparison with other natural hazards and disasters, drought is more important considering intensity and frequency as well as spatial extent and total damage. In the current research, the Standardized Precipitation Index (SPI) and Standardized Discharge Index (SDI) were used to analyze the temporal characteristics of droughts. To this end, monthly precipitation time series of 23 raingauge stations and 7 hydrometry stations across the Atrak River basin were used and SPI and SDI for six time intervals (3, 6, 9, 12, 24 and 48 months) were calculated and analyzed. For assessment of drought impact on surface water resources, first the correlation between rain and discharge time series of different lag times were calculated within the study area. Then, the Pearson correlation method was applied to calculate the correlation between SDI and SPI series for different time intervals at each individual subwatershed and whole watershed of the Atrak River. The results showed that the correlation between meteorological and hydrological droughts was significant at 99 percent confidence level. The maximum correlation was found for SPI and SDI of 3 months time intervals. This indicates that droughts cause decrease in surface flows and this impact is remarkably observed in the discharge values of the same month or one month later. The highest Pearson correlation was found for the Shirabad station and the Darband subwatershed.