*2.1. Introduction to CLDAS*

CLDAS is an isolatitude and longitude mesh fusion analysis product covering the Asian region (0–65◦ N, 60–160◦ E) with a resolution of 0.0625◦ × 0.0625◦ and 1 h, and a spatial geometric distance of 9 km between the corresponding grid points, including six variables: 2 m air temperature, 2 m specific humidity, 10 m wind speed, surface pressure, precipitation, and shortwave radiation. This dataset is developed by using the Space and Time Mesoscale Analysis System (STMAS), optimal interpolation (OI), probability density function matching (CDF), physical inversion, terrain correction, and other techniques based on ground and satellite observations from a variety of sources. The dataset's quality and spatio-temporal resolution in China is better and higher than in the international market. The scientific goal of CLDAS is to use data fusion and assimilation technology, on the ground observation, satellite observations, numerical model products, and other sources of data fusion to obtain high space-time resolution and high-quality temperature, pressure, humidity, wind speed, precipitation, and radiation elements such as lattice data to drive the land surface model, obtain soil temperature and humidity, etc. The research focuses on processing and acquiring land surface driving data, realizing the operation and integration of multiple land surface models, and improving the underlying surface data, vegetation parameters, and atmospheric driving data.

#### 2.1.1. Data Sources for CLDAS

(1) Ground observation data: hourly temperature, air pressure, humidity, wind speed, precipitation, and other data observed by more than 2400 national automatic weather stations and nearly 40,000 regional automatic weather stations after quality control.

(2) ECMWF (European Center for Mediumrange Weather Forecasts) numerical analysis/forecast products: global 3 h, 0.125◦ resolution 2 m temperature, 2 m humidity, 10 mU/V wind speed, surface pressure, and other data products released by EC (European Center).

(3) GFS numerical analysis/prediction products: NCEP released global ozone, atmospheric precipitation, surface pressure, and other data products with 3 h and 0.5◦.

(4) Satellite precipitation products: FY2 precipitation estimation products (nominal disk chart) of the National Satellite Meteorological Center; East Asia Multi-Satellite Integrated Precipitation Data Product (EMSIP) with a resolution of 1 h and 0.0625◦ for the Asian region operated by the National Meteorological Information Center.

(5) Fusion precipitation product: the fusion product of FY2/CMORPH precipitation and automatic ground station precipitation with 1 h and 0.1◦ resolution in China operated by the National Meteorological Information Center.

(6) FY2 satellite entire disk nominal map: multi-channel geostationary satellite observation data with 1 h and 5 km resolution (subsatellite point) of the Service of National Satellite Meteorological Center (nominal disk map).

(7) DEM data: a global 30m spatial resolution topographic data product jointly measured by NASA (National Aeronautics and Space Administration) and NIMA (National Bureau of Surveying and Mapping of the Ministry of Defense) was used to re-sample DEM topographic data with a spatial resolution of 0.0625◦ in the Asian region using the area weight method.
