分析发现ERA5中国区域数据在部分时段和个别年份存在显著偏差

ERA5数据在全球和中国区域气候变化研究方面发挥着至关重要的作用，近年来越来越得到研究者的广泛应用，但对于其在区域上的代表性的研究还非常初步。我们利用我们团队自己研发的高分辨温度数据集C-LSAT HR（1900-2024）作为基准，分析了ERA5在中国区域的表现，得到了一些非常有意思的结果：1）在众多的再分析数据集中，ERA5是表现最为突出的；2）1965-1966年由于缺乏中国区域的数据同化，ERA5在中国区域存在着显著的系统偏差和随机偏差。该结论可为此后对ERA5数据的用户提供一定的参考。

文章摘要如下：

Reanalyses are essential for climate change research and operational forecasting. Among the widely used reanalyses, ERA5 stands out as one of the most popular, with its latest version, extending back to 1940, released in 2023. However, a systematic comparative evaluation of ERA5's full-period dataset in China is lacking. This study compares the surface air temperature (SAT) data from ERA5 with those from four other extended reanalysis products (20CRv3, 20CRv3-ERA5, CERA-20C and ERA5-Land), using the recently updated C-LSAT HR as the benchmark dataset. The comparison focuses on climatology, long-term trends, and SAT variations over China. Our findings reveal that all three centennial-scale reanalyses significantly underestimate the warming trend in China since the early 20th century. Overall, ERA5 performs the best across all above evaluation aspects. However, the system and random errors in the years 1965 and 1966 are considerably larger than usual, primarily due to the lack of observations as input data. Further analysis using station observations as the “reference truth” shows that these anomalous errors persist throughout both years, with an overall cold bias of -0.74°C (1965) and -0.67°C (1966). The magnitude of the errors varies by season and region, with the most pronounced increase observed during the summer months. The MAE (MBE) in the summers of 1965 and 1966 increase by 0.44°C (-0.59°C) and 0.50°C (-0.65°C), respectively. Spatially, ERA5 records the largest system biases in the summer for southern Xinjiang and in the autumn for the Tibetan Plateau, with the MAE increase exceeding 3°C in these regions. The most significant contribution ratio of RMSE for abnormal years (IRMSE) occurs in the summer in South China and southern Xinjiang, where it exceeds 15% at most stations, although the average MAE increase for South China is only 1~2°C.

Lin J, Zhang H, Wei S, Xu Q, Li Z, Li Q*, 2025, Outstanding performance of ERA5 reanalysis temperature in China since 1950s and quantification of its abnormal error in 1965-1966, Quarterly Journal of the Royal Meteorological Society, accepted