Projection of changes in precipitation indices of the southern coast of the Caspian Sea in 2021-2050 period

Precipitation, as one of the most important elements of the hydrological cycle, is affected by climate change and this can lead to new conditions in water resources.In the present study, to monitor and simulation of Precipitation conditions in the southern coast of the Caspian Sea (Gilan and Mazandaran provinces), daily precipitation data of Astara, Rasht, Bandar Anzali, Ramsar, Gharakhil, Noshahr and Babolsar synoptic stations for base period 1986- 2015 from the Meteorological Organization and daily data for CanECM2 model with three scenarios RCP2.6, RCP4.5 and RCP8.5 from the Canadian Climatological Site was obtained. SDSM version 3.5 was used to simulate precipitation changes over the future period (2021-2050). After doing model calibration and validation, the downscaling of precipitation data was performed for the future period (2021-2050). Then, intensity, duration and frequency extreme indices of precipitation for the base and future periods were calculated. The results of three scenarios showed that the average annual precipitation in the study area increased, on average, by 20 to 70 mm as compared to base period (1986-2015). In addition, the results of analysis of precipitation indices showed an increase of precipitation with more than one mm in all weather stations and an increase of precipitation with more than 10 mm in most of the weather stations, excluding Babolsar and Gharakhil, in the future period 2021-2050 in comparison with the base period. However, the precipitation more than 20 mm was similar in the future and base period with a little change. The results revealed that a decrease in R95p and R99p indices at Ramsar and Nowshahr stations and an increase in the western and eastern parts will occurred in the future. Moreover, a decrease in the dry period length will happened in the future as compared to the base period. The extreme precipitation values are expected to be high for the region, which will increase the average annual precipitation.