## 2 Study Area and Datasets
### Datasets
#### 2.2.2 Data from the HiWATER Experiment  
As mentioned above, HiWATER was designed as a comprehensive ecohydrological experiment, and it was implemented in the HRB. MUSOEXE, a component of HiWATER, was implemented to reveal the spatial heterogeneities of heat and water fluxes by constructing two flux matrices [44]. In this study, EC data from 19 towers within the two matrices were used. The details of these EC systems are shown in Table 2, and the distribution of the stations is shown in Figure 1. EC16 and HHZ were excluded because they lacked surface net radiation (\(R_{n}\)) and soil heat flux observational data.  
The ground observation data include the H and latent heat flux (LE). The consistency of all of the EC systems and the quality of the data were ensured using the following steps. First, the consistency of the EC instruments was tested during an inter-comparison campaign in the flat, open Gobi desert, over a surface covered by coarse grain sand and small pebbles with with withered sparse scrub vegetation. This campaign was completed before HiWATER-MUSOEXE was conducted [29]. Second, all of the raw data were acquired at 10 Hz and processed. The processing included spike removal and corrections for density (WPL correction) [45; 46]. Third, a four-step procedure was performed to control the quality of the EC data; for more details, see [24; 29]. The soil heat flux (G) was measured by using three soil heat plates at a depth of 6 cm at each site, and the surface G was calculated based the soil temperature and moisture above the plates [47]. Energy imbalances are common in ground flux observations. To force the energy balance, the conserving Bowen ratio (H/LE) and the residual closure technique are often used. Computing the LE as a residual variable may be a better method for producing energy balance closure under conditions with large LE [48]. Thus, the residual closure method was applied because the \"oasis effect\" was distinctly observed in the desert-oasis system on clear days during the summer [24]. The data obtained during the HiWATER experiment can be freely obtained from the Heihe Plan Data Management Center ([[http://www.heihedata.org/](http://www.heihedata.org/)]([http://www.heihedata.org/](http://www.heihedata.org/))).  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Station** & **Latitude (\({}^{\circ}\)N)** & **Longitude (\({}^{\circ}\)E)** & **Elevation (m)** & **EBR** & **Sensor Height (m)** & **Dominant Land Cover** \\ \hline EC01 & 38.89322 & 100.35813 & 1552.75 & 1.01 & 3.8 & vegetables \\ EC02 & 38.88695 & 100.35406 & 1559.09 & 0.90 & 3.7 & maize \\ EC03 & 38.89053 & 100.37634 & 1543.05 & 0.94 & 3.8 & maize \\ EC04 & 38.87752 & 100.35753 & 1561.87 & 0.84 & 4.2 (6.2 after 19 August) & buildings \\ EC05 & 38.87574 & 100.35068 & 1567.65 & 0.82 & 3.0 & maize \\ EC06 & 38.87116 & 100.35970 & 1562.97 & 1.02 & 4.6 & maize \\ EC07 & 38.87676 & 100.36521 & 1556.39 & 0.93 & 3.8 & maize \\ EC08 & 38.87254 & 100.37649 & 1550.06 & 0.88 & 3.2 & maize \\ EC09 & 38.87239 & 100.38546 & 1543.34 & 0.81 & 3.9 & maize \\ EC10 & 38.87567 & 100.39572 & 1534.73 & 0.94 & 4.8 & maize \\ EC11 & 38.86991 & 100.34197 & 1575.65 & 0.92 & 3.5 & maize \\ EC12 & 38.86515 & 100.36631 & 1559.25 & 0.90 & 3.5 & maize \\ EC13 & 38.86074 & 100.37852 & 1550.73 & 0.99 & 5.0 & maize \\ EC14 & 38.85867 & 100.35310 & 1570.23 & 1.04 & 4.6 & maize \\ EC15 & 38.85551 & 100.37223 & 1556.06 & 0.89 & 4.5 & maize \\ EC17 & 38.84510 & 100.36972 & 1559.63 & 0.78 & 7.0 & orchard \\ SD & 38.97514 & 100.44640 & 1400.00 & 1.03 & 5.2 & swampland \\ SSW & 38.78917 & 100.49330 & 1594.00 & 0.81 & 4.6 & uncultivated land-desert \\ GB & 38.91496 & 100.30420 & 1562.00 & 0.90 & 4.6 & uncultivated land-Gobi \\ \hline \hline \end{tabular} Note: EBR represents energy balance closure, and the calculation method can be found in [28].  
\end{table}
Table 2: The eddy covariance system matrix of HiWATER-MUSOEXE.