# Spatiotemporal Analysis of Evapotranspiration and Effects of Water and Heat on Water Use Efficiency
## 2 Materials and Methods
### Evapotranspiration and Drought Index Data  
Gleam v3.3a (Global Land Evapotranspiration Amsterdam Model 3.3a) is a set of data estimating the different components of land surface evapotranspiration independently: actual evaporation (\(E\)), potential evapotranspiration (\(Ep\)), transpiration (\(Et\)), evaporation stress factor, root zone soil moisture, surface soil moisture, etc. [25]. This data product is based on the surface radiation and near-surface temperature of multiple reanalysis datasets, and the Gleam Ep dataset with a spatial resolution of 0.25\({}^{\circ}\)\(\times\) 0.25\({}^{\circ}\) is obtained by using the Priestley-Taylor formula. Evapotranspiration data are a monthly dataset ([[https://www.gleam.eu/](https://www.gleam.eu/)]([https://www.gleam.eu/](https://www.gleam.eu/))) (accessed on 14 October 2021). GLEAM evapotranspiration products have been widely used in the field of hydrology and meteorology since their development [26]. These data has been applied by scholars to the study of the arid region of northwest China, and the data quality has been verified accordingly [27; 28]. Therefore, monthly data of GLEAM V3.3A, \(E\), \(Ep\), and \(Et\) from 2000 to 2014 are used for data analysis.  
Two drought indices, SPEI and PDSI, were selected in this paper. The SPEI dataset is provided by the National Cryosphere Desert Data Center. ([[http://www.ncdc.ac.cn](http://www.ncdc.ac.cn)]([http://www.ncdc.ac.cn](http://www.ncdc.ac.cn))) (accessed on 14 October 2021). The spatial resolution is 1\({}^{\circ}\), and the temporal resolution is the monthly average from 2000 to 2014. The PDSI is the first comprehensive drought index developed and is most commonly used to assess the impact of drought on Agriculture in the United States. It was obtained from KNMI Climate Explorer ([[http://climexp.knmi.nl/](http://climexp.knmi.nl/)]([http://climexp.knmi.nl/](http://climexp.knmi.nl/))) (accessed on 14 October 2021), has a spatial resolution 1\({}^{\circ}\), and the temporal resolution is the monthly average from 2000 to 2014.  
Data Availability  
To verify the accuracy of GLEAM-\(E\) in Xinjiang region, the daily datasets from 34 sites of the China Meteorological Data Network ([[http://data.cma.cn/](http://data.cma.cn/)]([http://data.cma.cn/](http://data.cma.cn/))) (accessed on 14 October 2021) are used. Site scale assessment of surface evapotranspiration products was carried out. Due to the absence of observation data in time series, 132 valid observations were screened. The evaporating dish is the maximum evaporation condition of free water in the region under the condition of sufficient moisture [29]. In arid and semi-arid areas, the actual evapotranspiration is mainly determined by water and energy. At the same time, the evaporating dish evapotranspiration is not affected by moisture, and the main factor determining its size is solar energy. Therefore, the evaporating dish evapo  
Figure 1: Location of the study area (the small picture inserted shows the geographical location of Xin-jiang).  
transpiration has an inverse relationship with the actual evapotranspiration, and potential evapotranspiration represents the maximum evapotranspiration of an underlying solid surface under sufficient water supply [30]. It can be seen that the evapotranspiration in the evaporating dish is close to the potential evapotranspiration in the GLEAM product, and the feasibility of the GLEAM-_E_ product in the Xinjiang region can be verified by the correlation between the evapotranspiration and GLEAM-_Ep_. The results (Figure 2) show that there was a high correlation between the observations evapotranspiration and GLEAM-_Ep_. The correlation coefficient R\({}^{2}\) = 0.8654, indicating that the GLEAM-_E_ product had good verification accuracy in the Xinjiang region, and the verification results meet the requirements.