## 3 Results and Discussion
### Spatio-Temporal Variation of Terrestrial Ecosystems' GPP, ET, and WUE
The ET near the coastline had higher value, while the ET distribution in the summer was different than the GPP distribution. Since the plateau with higher ET value has lower temperature and air pressure values, there was lower ET in that area [51]. The global MOD16 terrestrial calculated ET was higher than in comparison with the ground measured ET at the GDK flux tower site as shown in Figure 10 [50]. Validation of the MODIS 16 global ET product was performed using flux tower measurements registered by the AsiaFlux network [50] and the results are presented in Figure 11 and Table 2. The fitted lines between the MODIS-based ET (y) and the flux tower measurement ET (x) were: y = 1.07x + 17.15, y = 1.07x + 17.15, y = 1.07x + 17.15, y = 1.07x + 17  
with a relatively high correlation coefficient, R = 0.76, bias = 2.52 g m\({}^{-2}\), RMSE = 9.84 kg m\({}^{-2}\) in 2007 and y = 1.26x + 18.90 with R = 0.83, Bias = \(-\)4.70 kg m\({}^{-2}\), RMSE = 10.41 g m\({}^{-2}\) in 2008. Understanding the spatial distribution of the WUE is significant to estimate the effect of the water cycle on the ecosystem carbon budget and to evaluate the spatial distribution of the water transferring capacity of ecosystems [18]. [PERSON] _et al_. [18] referred only to the temporal pattern of the WUE in different ecosystems, while we showed the spatial distribution map of the WUE (Figure 12). As shown in Figure 12(a,c), the WUE values near the coastline were higher than inland areas in dormant season because of overestimated GPP values near the coastline. Based on the spatial distribution of the WUE in the growing season (Figure 12(b,d)), the lower WUE was located in the inland area (cropland and rice paddy). The ET of cropland and rice paddy (irrigated region) was much higher than that of other areas [19,52]. The actual ET of rice paddy had similar values with potential ET because of high irrigation. Consequently, the WUE of the cropland was lower than other types of ground cover [19]. The WUE was high in areas located at higher elevations. The summit is located at higher elevation and therefore it has a lower air temperature which results in lower ET values [50]. Figure 13 describes correlated  
Figure 11: Time series of observed and estimated ET. Figure 10: Relationship between MODIS-based ET and flux tower measurement ET. relationship between the GPP and ET. The slope of the GPP-ET curvature in this figure represents WUE which was the ratio of GPP and ET. In dormant season, GPP and ET were correlated most significantly at GPP value less than 10 gC\(\cdot\)m\({}^{-2}\cdot\)8-day\({}^{-1}\) and at ET around the 0 to 5 g\(\cdot\)m\({}^{-2}\cdot\)8-day\({}^{-1}\) during 2007, whereas GPP and ET values were affected the WUE value in very little extent during 2008, with no correlation at higher values of GPP and ET during 2007 and 2008 (Figures 13 (a,c)). In contrast, in growing season, GPP and ET showed the positive relationship for all ranges, particularly GPP ranging from 10 to 50 gC\(\cdot\)m\({}^{-2}\cdot\)8-day\({}^{-1}\) and ET from 10 to 40 g\(\cdot\)m\({}^{-2}\cdot\)8-day\({}^{-1}\) (Figures 13(b,d)). Figure 13(b) showed the dense effect of GPP and ET values on WUE during 2007, whereas Figure 13(d) showed the spatially scattered effect of GPP and ET on WUE in 2008. We found that the seasonal mean of the WUE for the terrestrial ecosystem in 2007 was 2.86 g\(\cdot\)C\(\cdot\)g\(\cdot\)H\({}_{2}\)O\({}^{-1}\), ranging from 0.20 to 10.73 g\(\cdot\)C\(\cdot\)g\(\cdot\)H\({}_{2}\)O\({}^{-1}\) in the dormant season and the mean WUE was 1.81 g\(\cdot\)C\(\cdot\)g\(\cdot\)H\({}_{2}\)O\({}^{-1}\), ranging from 0.07 to 4.06 g\(\cdot\)C\(\cdot\)g\(\cdot\)H\({}_{2}\)O\({}^{-1}\) in the growing season.