ERA5-Land hourly data from 1950 to present

ERA5-Land (European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis) is a reanalysis dataset providing a consistent view of the evolution of land variables over several decades at an enhanced resolution compared to ERA5. ERA5-Land has been produced by replaying the land component of the ECMWF ERA5 climate reanalysis. Reanalysis combines model data with observations from across the world into a globally complete and consistent dataset using the laws of physics. Reanalysis produces data that goes several decades back in time, providing an accurate description of the climate of the past. ERA5-Land uses as input to control the simulated land fields ERA5 atmospheric variables, such as air temperature and air humidity. This is called the atmospheric forcing. Without the constraint of the atmospheric forcing, the model-based estimates can rapidly deviate from reality. Therefore, while observations are not directly used in the production of ERA5-Land, they have an indirect influence through the atmospheric forcing used to run the simulation. In addition, the input air temperature, air humidity and pressure used to run ERA5-Land are corrected to account for the altitude difference between the grid of the forcing and the higher resolution grid of ERA5-Land. This correction is called 'lapse rate correction'. The ERA5-Land dataset, as any other simulation, provides estimates which have some degree of uncertainty. Numerical models can only provide a more or less accurate representation of the real physical processes governing different components of the Earth System. In general, the uncertainty of model estimates grows as we go back in time, because the number of observations available to create a good quality atmospheric forcing is lower. ERA5-land parameter fields can currently be used in combination with the uncertainty of the equivalent ERA5 fields.

ERA5-Land（欧洲中期天气预报中心（ECMWF）再分析数据集）是一款再分析数据集，相较于ERA5，它以更高的分辨率提供了数十年来陆地变量演变的一致视图。ERA5-Land通过重演ECMWF ERA5气候再分析的陆地分量模块生成。再分析技术将数值模式数据与全球各地的观测数据相结合，依据物理定律构建出一套全球完整且一致的数据集。再分析可生成数十年前的历史数据，精准刻画过去的气候状况。

ERA5-Land以ERA5大气变量（如气温、空气湿度）作为输入，用以约束模拟的陆地场，这一过程被称为大气强迫（atmospheric forcing）。若缺乏大气强迫的约束，基于模式的估算结果会快速偏离真实情况。因此，尽管ERA5-Land的生产过程未直接使用观测数据，但这些观测数据可通过用于运行模拟的大气强迫产生间接影响。此外，运行ERA5-Land所需的输入气温、空气湿度与气压数据，会针对强迫场网格与ERA5-Land更高分辨率网格之间的海拔差异进行校正，该校正过程被称为‘递减率校正（lapse rate correction）’。

与其他模拟结果一样，ERA5-Land数据集提供的估算结果存在一定程度的不确定性。数值模式仅能或多或少精准地再现支配地球系统不同组分的真实物理过程。总体而言，模式估算的不确定性会随回溯时间的增加而增大，因为用于生成高质量大气强迫的可用观测数据会随之减少。目前，ERA5-Land的参数场可与等效ERA5场的不确定性相结合使用。