The newly released simulations from the Sixth Phase of the Coupled Model Intercomparison Project (CMIP6) provide an opportunity to re‐examine long‐term soil moisture trends. In this study, we assessed the historical simulation (1850–2014) of surface soil moisture from 18 general circulation models that are part of CMIP6 and compared them with model simulations from CMIP5 and NLDAS‐2, and in situ observations over CONUS. Our results show that for CONUS as a whole, there is no significant long‐term trend in soil moisture, but significant drying trends exist over medium‐term, short‐term, and near‐present periods based on the CMIP6. Our comparison of CMIP6 to NLDAS‐2 (1980–2014) and in situ observations (2004–2014) demonstrates that it more accurately captures soil moisture trends in CONUS than CMIP5. CMIP6 shows a significant wetting trend in the Northwest, Midwest, Northeast, and Southeast. There is greater agreement amongst the individual models in CMIP6 than CMIP5, but intermodel variability still exists.

中文翻译：

---

连续美国表层土壤水分的历史变化：CMIP6的评估

耦合模型比较项目（CMIP6）第六阶段的最新发布的模拟提供了一个重新检查土壤长期水分趋势的机会。在这项研究中，我们评估了CMIP6的18个通用循环模型中的表面土壤水分的历史模拟（1850年至2014年），并将其与CMIP5和NLDAS-2的模型模拟以及CONUS上的现场观测进行了比较。我们的结果表明，对于整个CONUS，基于CMIP6，土壤水分没有明显的长期趋势，但是在中期，短期和近乎当前的时期内，存在明显的干燥趋势。我们将CMIP6与NLDAS-2（1980-2014）和现场观测结果（2004-2014）进行了比较，结果表明，与CMIP5相比，它可以更准确地捕获CONUS中的土壤水分趋势。CMIP6在西北，中西部，东北和东南部显示出明显的润湿趋势。与CMIP5相比，CMIP6中的各个模型之间的共识更大，但是模型间的可变性仍然存在。