## 4 Results and Discussion
### Variations in Monthly ET, GPP, and WUE for 12 Irrigation Districts  
To quantitatively understand oasis agricultural water consumption, cropland biomass production, and water product between irrigation districts, histograms of the average monthly ET for the Daman, Shangsan, Ganjun, Yingke, Xigan, Wujiang, Liyuan River, Shahe, Liaoquan, Yanuan, Banqiao, and Pingchuan districts, which represent the oasis agricultural areas in the identified geographic locations, are plotted for all months from 2010 to 2016 (Figure 6). The monthly regional ET from 2010 to 2016 is plotted in Figure 6 (first column), with the seasonal variations of each irrigation district showing a unimodal curve with a peak in July. From June to August in all years, the average monthly regional ET in each irrigated area generally changed directly from 120 to 150 mm; however, there were certain exceptions. For example, in 2011 and 2015, the maximum monthly regional ET value in the Ganjun irrigation district was approximately 75 mm. On the other hand, the maximum value in the Shangsan and Banqiao districts in 2010, Shangsan and Xigan and Daman districts in 2014, and Shangsan irrigation district in 2016 exceeded 150 mm. The seasonal patterns of ET in the oasis agricultural area in the arid and semi-arid region of Northwest China are distinct from those of moist areas of the same latitude in the North China Plain (NCP) [97]. This is because single crops account for the majority of the former, and double crops in rotation account for the majority of the latter. The monthly regional patterns (seasonal variations) in GPP and WUE have a strong resemblance to ET for different irrigation districts, as shown in Figure 6 (second and third columns). However, the monthly spatial variation patterns are different from the amplitude changes and CV statistical indicators for the different irrigation districts (Figure 6, red stars). At the irrigated area scale, ET had the smallest spatial variation, GPP had the largest spatial variability, and WUE was in the middle. Numerous studies reported that the primary irrigation method in midstream oasis agricultural areas has always been flood irrigation from the surface and groundwater [61]. In other words, each irrigated area has a sufficient water supply during the growing season. In addition, the crop for the entire oasis is mostly field corn. Therefore, the differences in ET for each irrigated area are relatively small. However, in addition to the influence of irrigation, other anthropogenic activities, such as changing the amount of fertilizer applied and renewing plant varieties, also greatly affect the changes in GPP for each irrigated district. Previous studies in the NCP have proved this [98; 99]. As a result, GPP showed stronger variability in years with both large (2011 and 2015) and small (2010 and 2013) ET seasonal changes among the 12 irrigation districts. The spatiotemporal variability of WUE is jointly affected by ET and GPP. In general, a higher monthly ET also means a greater GPP, which gives a higher WUE for each irrigation district (Figure 6). More importantly, at the monthly scale, WUE values of the oasis croplands the early (May) and late (June) growing seasons are close to the mid-growing season (July and August) (Figure 6, third column). The early WUE was slightly lower because ET added in the early stage was significantly faster than GPP, while ET added in the later stage showed a synchronous decrease (nearly linear), which is confirmed in the following, with bivariate histograms between monthly ET and GPP. This is an important finding and indicates the factors that describe monthly WUE and water-saving irrigation time allocation schemes in midstream oasis agricultural areas. Figure 6: Cont. Figure 6: Spatiotemporal patterns of monthly average ET, GFP, and WUE composites of cumulative daily ET, GFP, and WUE for 12 irrigation districts for all months in 2010-2016 over midstream across agricultural areas.