## 2 Materials and Methods
### Data  
The ratio of GPP to ET data elucidates the intricate spatial and temporal variations in China's WUE over the long term. This investigation employs the Global Land Surface Characteristic Parameter Data Product (GLASS) based on MODIS sourced from the National Earth System Science Data Center ([[http://www.geodata.cn](http://www.geodata.cn)]([http://www.geodata.cn](http://www.geodata.cn))). The GLASS prod  
Figure 1: Study area and climate zone ((**a**–**f**) shows the multi-year average values of LAI (leaf area index), RAD (solar radiation), TEM (temperature), PRE (precipitation), SM (soil moisture), VPD (vapor pressure deficit) from 2001–2020 and I–VII means the distribution of climate zones in the study area, there into I is mid-temperate arid region; II is mid-temperate semi-arid region, III is mid-temperate and semi-humid region, IV is plateau temperate semi-arid region, V is warm temperate semi-humid region, VI is northern subtropical humid region, VII is edge tropical warm region).  
uct represents a comprehensive and meticulously assembled global dataset, generated through inversion techniques that incorporate a variety of remote sensing data and in situ ground measurements.  
The climate variables analyzed in this study included TEM, PRE, and RAD. The TEM and PRE datasets were acquired from the National Tibetan Plateau Data Center Third Pole Environment Data Center (TPDC), whose dataset was downscaled on the basis of global 0.5\({}^{\circ}\) climate data from the climatic research unit (CRU) and WorldClim [38; 39]. These datasets have been further validated using 496 independent meteorological observation stations in China, and the results are reliable. In addition, these data are monthly averages with a spatial resolution of 0.0083\({}^{\circ}\) and cover a time range of January 1901-December 2023. China's net solar radiation dataset from 1982 to 2020 was used in this study. The data are based on the European Centre for Medium-Range Weather Forecasts Reanalysis 5 (ERA5) net surface radiation (SSR) data and were interpolated and reconstructed via CDO software to obtain net surface radiation data in China [40].  
The MOD17 data product, which is based on NASA's MODIS, was used for the LAI in this study. This dataset spans the period from February 2000 to the present, with an 8-day interval and a spatial resolution of 500 m. In the present investigation, the TerraClimate dataset, accessible at [[https://www.climatologylab.org/terraclimate.html](https://www.climatologylab.org/terraclimate.html)]([https://www.climatologylab.org/terraclimate.html](https://www.climatologylab.org/terraclimate.html)) (accessed on 16 March 2024), was employed to delineate the VPD values across China. TerraClimate is a comprehensive monthly climate and climate water balance dataset that covers the entire global landmass. Leveraging climate-guided interpolation techniques, it integrates the spatially precise climate norms derived from the WorldClim dataset with temporally variable yet spatially coarser data sourced from CRUTs 4.0 and the Japanese 55-year reanalysis (JRA55), resulting in a spatially detailed dataset encompassing a broadened temporal scope [41]. The present study employed the global daily surface soil moisture dataset, which boasts a spatial resolution of 1 km and spans the period from 2000 to 2020. This dataset combines the European Space Agency-Climate Change Initiative (ESA-CCI) surface soil moisture, surface soil moisture from the ERA5 reanalysis dataset and International Soil Moisture Network in situ observations, and other optical remote sensing datasets based on the random forest algorithm to produce the surface soil moisture at 1 km resolution [42]. The above data were resampled to 0.05\({}^{\circ}\) via bilinear interpolation in ArcGIS for calculation and analysis.