An Analysis of the Relationship between Meteorological and Hydrological Droughts: A Case Study of Kashkan Watershed, Lorestan Province, Iran

Drought is a natural phenomenon with dangerous consequences in all regions of the world. Scientists have proposed several indices for drought evaluation and monitoring which are designed based on the use of meteorological variables and different computational methods. In this research, SPI and SDI indices were used to analyze the temporal characteristics of droughts. The data of daily precipitation and discharge time series of 5 rain gauges and hydrometric stations across Kashkan watershed in Lorestan province from 1969-1970 to 2012- 2013 were used and the value of SPI and SDI for six time intervals (3, 6, 9, 12, 24 and 48 months) were calculated and analyzed. For assessing the effect of droughts on discharge, Pearson correlation method was applied to calculate the correlation between SDI and SPI series for different time intervals, and different time lags were calculated at each station of the Kashkan river basin. The results showed that the correlation between meteorological and hydrological droughts was statistically significant at 99 and 95 percent confidence level. The maximum correlation was found for SPI and SDI of 9 and 12 months time intervals. This indicates that droughts decrease surface flows which strongly affect the discharge values of the same month or the following one or two months.