*Article* **Assessment of Daily of Reference Evapotranspiration Using CLDAS Product in Different Climate Regions of China**

**Li-Feng Wu 1,2,†, Long Qian 3,†, Guo-Min Huang 1, Xiao-Gang Liu 3,\*, Yi-Cheng Wang 2, Hua Bai <sup>1</sup> and Shao-Fei Wu <sup>1</sup>**


**Abstract:** Reference Crop evapotranspiration (*ET*0) datasets based on reanalysis products can make up for the time discontinuity and the spatial insufficiency of surface meteorological platform data, which is of great significance for water resources planning and irrigation system formulation. However, a rigorous evaluation must be conducted to verify if reanalysis products have application values. This study first evaluated the ability of the second-generation China Meteorological Administration Land Data Assimilation System (CLDAS) dataset for officially estimating *ET*<sup>0</sup> (the local meteorological station data is used as the reference dataset). The results suggest that the temperature data of CLDAS have high accuracy in all regions except the Qinghai Tibet Plateau (QTP) region. In contrast, the global solar radiation data accuracy is fair, and the relative humidity and wind speed data quality are poor. The overall accuracy of *ET*<sup>0</sup> is acceptable other than QTP, but there are also less than 15% (103) of stations with significant errors. In terms of seasons, the error is largest in summer and smallest in winter. Additionally, there are inter-annual differences in the *ET*<sup>0</sup> of this data set. Overall, the CLDAS dataset is expected to have good applicability in the Inner Mongolia Grassland area for estimating *ET*0, Northeast Taiwan, the Semi Northern Temperate zone, the Humid and Semi Humid warm Temperate zone, and the subtropical region. However, there are certain risks in other regions. In addition, of all seasons, summer and spring have the slightest bias, followed by autumn and winter. From 2017 to 2020, bias in 2019 and 2020 are the smallest, and the areas with large deviation are south of climate zone 3, the coastal area of climate zone 6, and the boundary area of climate zone 7.

**Keywords:** raw reanalysis data; grid data; reference evapotranspiration; meteorological variables; Penman-Monteith equation
