Although much progress has been made in identifying the large-scale drivers of recent summer precipitation variability in North China, the evolution of these drivers over longer time scales remains unclear. We investigate multidecadal and interannual variability in North China summer precipitation in the 110-year Coupled ECMWF Reanalysis of the Twentieth Century (CERA-20C), considering changes in regional moisture and surface energy budgets along with nine circulation indices linked to anomalous precipitation in this region. The CERA-20C record is separated into three distinct periods according to the running climatology of summer precipitation: 1901–1944 (neutral), 1945–1979 (wet), and 1980–2010 (dry). CERA-20C reproduces expected relationships between large-scale drivers and regional summer precipitation anomalies well during 1980–2010, but these relationships generally do not extend to earlier periods. For example, a strong relationship with the Eurasian teleconnection pattern only emerges in the late 1970s, while correlations with the El Niño-Southern Oscillation and the Pacific–Japan pattern change sign in the mid-twentieth century. We evaluate two possible reasons for this nonstationarity: (1) the underlying atmospheric model may require strong data assimilation constraints to capture large-scale circulation influences on North China, or (2) large-scale drivers inferred from recent records may be less general than expected. Our analysis indicates that both factors contribute to the identified nonstationarity in CERA-20C, with implications for the reliability of seasonal forecasts and climate projections based on current models.

中文翻译：

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CERA-20C再分析中华北地区潜在大尺度驱动因素与夏季降水之间关系的长期变化

尽管在确定华北地区近期夏季降水变化的大规模驱动因素方面已取得了很大进展，但这些驱动因素在较长时间范围内的演变仍不清楚。我们研究了二十世纪110年ECMWF耦合再分析（CERA-20C）中华北夏季降水的年代际变化和年际变化，考虑了该地区的湿度和地表能量收支变化以及与该地区异常降水相关的9个环流指数。根据夏季降水的运行气候，CERA-20C记录分为三个不同的时期：1901-1944（中性），1945-1979（湿）和1980-2010（干）。CERA-20C很好地再现了1980-2010年期间大规模驱动因素与区域夏季降水异常之间的预期关系，但是这些关系通常不会扩展到更早的时期。例如，与欧亚遥相关模式的紧密关系仅在1970年代后期才出现，而与厄尔尼诺-南方涛动和太平洋-日本模式的相关关系则在20世纪中叶改变。我们评估了这种不稳定现象的两个可能原因：（1）潜在的大气模型可能需要强大的数据同化约束才能捕获对华北的大规模环流影响，或者（2）从最近的记录中推断出的大规模驱动力可能不如预期。我们的分析表明，这两个因素均导致CERA-20C的非平稳性，并影响了基于当前模型的季节预报和气候预测的可靠性。