Predicting drought impact on the Caspian Sea coast affected by climate change

Introduction: The phenomenon of climate change can have different effects on different systems. Due to the vital role of water in human life, the study of its negative effects on the occurrence, severity and duration of drought is of particular importance. In this study, the effects of climate change on droughts on the southern shores of the Caspian Sea in future periods will be evaluated
Material and methods: The region under study covers three northern provinces of Gilan, Mazandaran, which Golestan and covers  four percent in terms of area and 12 percent in terms of population of the whole Iran. In this study, the effects of climate change on droughts on the southern shores of the Caspian Sea in future periods will be evaluated. For this purpose, precipitation data from the HadCM3-A2 general circulation model for future periods (2099-2070, 2069-2040, 2039-2010) have been scaled statistically and while considering the uncertainty of climate fluctuations in the 20 series. At first, daily precipitation was produced. Then the standardized precipitation index was calculated for the monitoring period and future periods. Finally, the downscaled variables of the region were compared with the observed variables and after ensuring the ability of the HadCM3 model in downscaling temperature and precipitation variables of the region, observed daily time series of precipitation and temperature and large-scale variables from HadCM3 model in the periods of 2010-2039, 2040-2069, and 2070-2099) were fed to the SDSM model.
Results and discussion: The results obtained from the output of this index in the monitoring period and future periods with different time scales show that the intensity of drought in the coming decades will increase compared to the monitoring period. This increase is more severe for the east of the Caspian Sea, so that the intensity of the drought in the 2080s will be three times the observation period. The results indicated that the climate change results in an increase in the frequency and severity of drought in the studied region. Findings of the present research indicate that in spite of the existence of variability in the SPI lower than 9 months, it has increased 25 and 23.5% in longer periods of 1 to 2 year periods in comparison with the historical period. The incompatibility of drought simulated in the future with observation period in Gorgan station with four remaining stations of the southern regions of the Caspian Sea should be noted.  This situation may be due to differences in the resources of precipitation in the eastern and western coasts of the Caspian Sea and different response of two regions against the global warming. Different studies such as Alijani (1991) indicated that the Caspian Sea west coasts are more affected by the northerly flows of Siberian high pressure system than its east coasts, and in case of the establishment of the high pressure over Caspian Sea, precipitations in the west of the Caspian Sea will be higher than its eastern region. The phenomenon of global warming has resulted in weakening the Siberian high pressure system in general. Therefore, the degree of the reduction in precipitations in central and western regions of the Caspian Sea will be relatively higher than in its eastern regions such as Gorgan station.
Conclusion: Occurrence of successive droughts and increasing drought intensity in the coming decades of the southern Caspian coastal areas will reduce water resources and the region-based economy will face a more severe crisis, in which case water resources management and development of strategic irrigation document and cultivation pattern a region compatible with socio-economic and climatic trends seems absolutely necessary.