## 4 Discussion
The above analysis shows that the spatial and temporal characteristics of the vegetation WUE in Gansu Province are closely related to the water and temperature conditions of the environment and that precipitation has a higher influence on vegetation WUE than air temperature. Cultivated vegetation in Gansu Province is mostly concentrated in the Hexi Corridor area, as well as Dingxi and Longnan, where adequate light conditions are conducive to plant growth; however, due to the suboptimal irrigation system, there is a large amount of water waste, with about 70% of the canalized water being lost in the form of seepage and evapotranspiration [40], so the WUE in the area is not very high (1.23 gC\(\cdot\)mm\({}^{-1}\cdot\)m\({}^{-2}\)). In terms of g/kg, this means that vegetation fixation requires the evapotranspiration of 1 kg of water for every 1.23 gC. For the last 20 years, WUE has been decreasing continuously, so how to improve the irrigation WUE of oasis farmland is an issue of concern. It has been shown that VPD has a significant effect on vegetation WUE, and the larger the VPD is, the stronger the carbon sequestration capacity is and the larger the transpiration water consumption is. This is mainly because an increase in VPD makes the atmosphere more arid, which increases transpiration and water balance in plants but also leads to limiting mechanisms, such as stomatal closure in photosynthesis [41]. In addition, the increase in VPD may also affect a range of physiological and metabolic processes by modulating stomatal conductance, which in turn may play an important role in plant growth and development [42]. In studies exploring the characteristics of WUE change in Gansu Province, the main data used have been vegetation-type data. However, human activities have also had an impact on the transformation of land types and introduced uncertainties. Nevertheless, it is expected that future WUE changes in Gansu Province will not lead to a large-scale decrease, but rather a possible reversal of the phenomenon, i.e., a shift from a decreasing to an increasing trend, although the exact reason for this is not yet clear. Therefore, how to clarify the possible dynamics of WUE in Gansu Province in the future is the next step to be carried out. In this study, the temporal and spatial dynamic characteristics of vegetation WUE in Gansu Province were analyzed, and the future development of this indicator was predicted, but the spatial resolution characteristics of remote sensing data inevitably affected the results. We focused on the influence of natural factors on vegetation WUE, but these factors are comprehensive and complex, and a large number of studies have been carried out to analyze them at different scales and with various methods; therefore, other factors, such as drought conditions [43], human activities [44], and CO\({}_{2}\)[45], should also be considered, and their influence on WUE quantitatively differentiated. In addition, in terms of climatic impacts, mean annual temperatures cannot represent temperature changes at the month or even week level, but sudden temperature changes may have a greater impact on plants and their WUE. How all these factors affect WUE in Gansu Province needs to be further analyzed and will be the aim of further work.