Projected Changes in Extreme Precipitation over Haihe River Basin Based on a Variable-Resolution Community Earth System Model

The simulation capabilities of the Uniform Resolution Community Earth System Model (UN-CESM) and Variable-Resolution Community Earth System Model (VR-CESM) for climatological precipitation and extreme precipitation in the Haihe River Basin (HRB) during 1976–2005 were evaluated using the daily gridded climate observation dataset CN05.1. Further analysis was conducted on the spatial and temporal characteristics of extreme precipitation over the HRB based on the VR-CESM precipitation estimation under the RCP8.5 scenario for 2021–2050. Compared with those of UN-CESM resolution: 1°(latitude)×1°(longitude), the results of VR-CESM compensate for the low resolution of global models in watershed scale simulations. The overall simulation effect is also improved. VR-CESM resolution in HRB: 0.125°(latitude)×0.125°(longitude) shows an enhanced accuracy in simulating the frequency of extreme precipitation in the southwestern part of the HRB and southern Yanshan and the intensity of extreme precipitation in the northern part of the eastern plain. With 1976–2005 as the base period, VR-CESM projects that the annual precipitation will decrease in the northern part of the HRB and increase in the central and southern regions of the HRB during 2021–2050. The precipitation in the southeastern HRB will generally increase by more than 10% in July. The projected frequency of heavy precipitation is bounded by 38° N and shows a decreasing trend in the north and an increasing trend in the south, with almost a 20% increase in the border area of the four southern provinces (Hebei, Henan, Shanxi, and Shandong Province). The projected increases in the maximum precipitation for 5 consecutive days mostly occur in the northern part of Beijing, the central parts of the Taihang Piedmont Plain, and the border regions of Shandong, Hebei, and Henan provinces, with the increasing magnitude of RX5day larger than 80% compared with the baseline period. The results for the precipitation, frequency, and intensity of extreme rainfall indicate significant spatiotemporal heterogeneity in the risk of extreme rainfall in the HRB, implying the potential complexity of dealing with extreme precipitation in the HRB in the future.