Historical Changes and Future Projections of Extreme Temperature and Precipitation along the Sichuan–Tibet Railway

Based on multiresource high-resolution in situ and satellite merged observations along with model simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX), this study first investigated historical changes in extreme temperature and precipitation during the period of 1979–2018 in areas along the Sichuan–Tibet Railway, and then projected the future changes in the frequency and intensity of extreme temperature and precipitation under the RCP (Representative Concentration Pathway) 4.5 and 8.5 scenarios. This paper is expected to enhance our understanding of the spatiotemporal variability in the extreme temperature and precipitation along the Sichuan–Tibet Railway, and to provide scientific basis to advance the Sichuan–Tibet Railway construction and operation. The results show that temperatures in the Sichuan–Tibet region display a noticeable warming trend in the past 40 years, and the increase of minimum temperature is significantly higher than that of maximum temperature in the northwest of the region. Significant increase of precipitation is found mainly over the northwest of the Tibetan Plateau. Except for Lhasa and its surrounding areas, precipitation over other areas along the Sichuan–Tibet Railway shows no significant change in the past 40 years, as indicated in five datasets; however, precipitation along the railway has shown a remarkable decrease in the past 20 years in the TRMM satellite dataset. The warm days and nights have clearly increased by 6 and 5 day decade⁻¹ for 1979–2019, while cold days and nights have markedly decreased by about 6.6 and 3.6 day decade⁻¹, respectively. In the past 20 years, the areas with increased precipitation from very wet days and extremely wet days are mainly distributed to the north of the Sichuan–Tibet Railway, while in the areas along the railway itself, the very wet days and extremely wet days are decreasing. Under RCPs 4.5 and 8.5, the temperature in the Sichuan–Tibet region will increase significantly, and the frequency of extreme high (low) temperature events in the late 21st century (2070–2099) will greatly increase (decrease) by about 50%–80% (10%) compared with occurrences in the late 20th century (1970–1999). Meanwhile, the frequency of very wet days and extremely wet days in the Sichuan–Tibet region will increase by about 2%–19% and 2%–5%, respectively, and the areas along the Sichuan–Tibet Railway will be affected by more extreme high temperature and extreme precipitation events.