Precipitation Projection in Lake Urmia Basin in East Azerbaijan, Iran Using Downscaling of Selected CMIP6 Models

Lake Urmia, one of the largest saltwater lakes in the world, has experienced a significant decrease in water levels in recent decades. Climate change has been identified as one of the main factors contributing to this reduction. Increases in temperature and changes in precipitation patterns are among the effects of climate change that have led to a decrease in water resources. In this study, five General Circulation Models (GCMs) have been used, including GFDL, MRI, MPI, BCC, and CMCC, to examine precipitation projections in the eastern basin of Lake Urmia under climate scenarios. The precipitation output of the mentioned models has been statistically downscaled using CMHyd software. The selection of GCM models was based on access to their data and their ability to simulate the stations observed precipitation. In the downscaling process, data from three synoptic stations have been used. The observational base period of 1985-2014 and future periods are considered 2026-2050 as near future, 2051-2075 as medium future and 2076-2099 as far future. Also, the future precipitation was predicted under three scenarios: optimistic, moderate and pessimistic, SSP1-2.6, SSP2-4.5 and SSP5-8.5, respectively. The precipitation was studied annually and the changes of precipitation in each of the next three periods compared to the base period of observations and then their significance was examined at a confidence level of 5%. In the optimistic scenario, most models for the periods 2026-2050 and 2051-2075, except for the Tabriz station, indicate a decrease in annual precipitation, and in the period 2076-2099, all stations experience an increase in precipitation which is not significant. In the pessimistic scenario, the BCC, GFDL and CMCC models reveal a decrease in annual precipitation, which in the BCC model is significant for the period 2076-2099. In the middle scenario, except for the GFDL and MRI models which present an increase in precipitation, other models exhibit a decrease in precipitation for all three periods and across all stations. Based on the expected decrease in precipitation in the coming years, and to prevent further drying of Lake Urmia, a national water management program to counteract climate change should be developed.

Keywords: Urmia Lake, Climate change, Precipitation, CMIP6, CMHyd.