Historical trend analysis and future projections of precipitation from CMIP5 models in the Alborz mountain area, Iran

Abstract

Precipitation changes in annual and seasonal time series over the Alborz Mountains area during 1950–2014 were analyzed using historical observations from 154 rain gauge stations. The projected changes in precipitation for the twenty-first century were evaluated using three Coupled Model Intercomparison Project Phase 5 (CMIP5) datasets. Trends in the precipitation time series were detected by linear regression and its significance was tested by t test. Mann–Kendall rank test (MK test) and Sen’s slope estimator were also employed to confirm the results. Sequential Mann–Kendall test (SQ-MK test) was also applied for change point detection in annual and seasonal precipitation time series. Pre-whitening was used to eliminate the influence of serial correlation on the MK test. Future precipitation was analyzed by GFDL-CM3, HadGEM2-AO and MPI-ESM-MR models under two representative concentration pathways (RCP) RCP 4.5 and RCP 8.5 scenarios. The analysis of the historical precipitation series indicated an insignificant trend in the annual and seasonal series at most stations. The highest numbers of stations with negative significant trends occurred in winter and with positive significant trends in summer. The results of change point detection in annual and seasonal precipitation series show that most of the significant mutation points began in the 1970s. The future projections showed that precipitation may decrease according to most of the models under the RCP 4.5 and RCP 8.5 scenarios, while the decrease may not be large, except in the summer season for the end of this century.