Evaluation of historical and future precipitation changes in CMIP6 over the Tarim River Basin

Precipitation directly affects the socioeconomic development in the inland river basins of the arid regions of Northwest China. However, the scarcity of observed data makes it hard to adequately investigate precipitation changes. To help solve this problem, we evaluated the precipitation patterns and trends of 19 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) in the northern mountains, central basin, and southern mountains of the Tarim River Basin based on observed data from 1965 to 2014, and conducted a comparison with CMIP5. The results showed that the CMIP6 models have spatial differences in capturing the monthly precipitation over the Tarim River Basin. Although it can capture the changes in monthly precipitation of mountains and basins, it does not capture the monthly maximum precipitation in mountains quite well. CMIP6 models capture precipitation with greater deviations in the wet season than in the dry season, especially for the peak precipitation in June and July. Underestimation of annual precipitation in the northern mountains is common in CMIP6 models with the RMSE of 42.51–50.55 mm. Most models capture the wetting trends in the southern mountains, but their reproduction of wetting trends in the northern mountains differs significantly in coverage. The change rates of annual precipitation from 2015 to 2100 in the northern mountains, central basin, and southern mountains under SSP2-4.5 and SSP5-8.5 are 0.20–0.29 mm/a, 0.10–0.18 mm/a, and 0.23–0.49 mm/a, respectively. The wetting trend in the Tarim River Basin is significantly higher under SSP5-8.5 than under SSP2-4.5. The comparison between CMIP5 and CMIP6 indicates that CMIP6 models are generally able to capture its fluctuating characteristics. However, there is no single model that can simultaneously represent the observed precipitation changes in the Tarim River Basin, especially for the differences in basins and mountains.