Investigating the Relationship between Hydrological and Meteorological Droughts Using SPI, RDI and SDI Indices with an Emphasis on Comparing Two Different Methods of Calculating ET0 (Case Study: Sufi Chai Basin of Maragheh)

For the optimal management of the surface water, it is necessary to identify the effect of meteorological drought on the river flows in terms of time. In this study, the relationship of meteorological and hydrological droughts in Sufi Chai River basin of Maragheh (East Azarbaijan province) was evaluated using SPI, RDI and SDI. The daily weather data of the Maragheh synoptic station and the daily data of Tazehkand hydrometric station (upstream of Alavian dam) were used. The statistical period of 34 years were determined (1983-2017) and 3, 6, 12, 24 and 48 month time series were created. In RDI, ETO was calculated using FAO-Penman-Monteith and Hargreaves-Samani methods. The correlation of hydrological and meteorological indices was performed for 3 to 48 month time series without delay and with delay of one-five month. The results in without delay condition showed the highest correlation between the indices is belonged to the series with similar period. The correlation between the similar RDIFPM and SDI series were less than the ones corresponding to SPI and SDI, or RDIHS and SDI. It is concluded considering the other weather parameters, in addition to rainfall, for calculating the indices, results in reduction of the correlation between the meteorological and hydrological indices. Among RDIHS and SDI values with delay condition, in the 3, 6 and 12 time series, the greatest effect of the meteorological drought on river flow was observed with the 3 month delay and in the 24 and 48 month time series, this effect was simultaneous.