Investigating the drought characteristics of Tamar basin (upstream of Golestan Dam) using SPI and SPEI indices under current and future climate conditions

To predict climate change and its effect on drought future situation in Tamar Basin, first daily output data of CanESM2 model downscaled and predicted by SDSM model and also RCP 2.6 and RCP 8.5 scenarios in the 2020-2049 period. Then, drought conditions evaluated by predicted data and SPI and SPEI indices in the future. Trend analysis of temperature and precipitation variables also carried out by Mann-Kendall non-parametric test. The results of trend analysis showed that precipitation changes is negligible and increase of temperature in most time series is significant. The performance of SDSM model to predict temperature and precipitation data is also very suitable and its outputs showed that temperature and precipitation have increased rather than that in the baseline period. The results of SPI index indicated that in both the periods the most droughts and wets have occurred at the late and first half of the two periods respectively. Evaluation of drought by SPEI index showed more severe drought rather than SPI index and according to increase of temperature trend in the baseline period and also temperature increase in the future can say the results of SPEI index are more actual and logical than the results of SPI index.