# The Response of NDVI to Climate Change in the Lowest and Hottest Basin in China
## 4 Discussion
However, this study observed a positive correlation between PET and NDVI in the oasis-desert transition zone, which may be attributed to the replenishment of shallow groundwater or the water regulation effects of irrigation systems. This finding aligns with [PERSON] et al. 's conclusion in the Mongolian Plateau, which indicates that human activities (such as groundwater extraction) can indirectly enhance vegetation adaptability to evapotranspiration by alleviating water limitations [36]. It is crucial to highlight that the PET estimation method employed in this study not only incorporates mean temperature but also integrates critical information like diurnal temperature ranges. This enables a more comprehensive characterization of the pronounced potential evaporation demand in continental arid zones like the Turpan-Hami Basin. The latest study by [PERSON] et al. confirmed through eddy covariance observations that in arid regions influenced by irrigation, the positive correlation between PET and gross primary productivity (GPP) arises from the adaptive regulation of vegetation stomatal conductance in response to water supply [37]. Indirect support comes from [PERSON] et al. 's research in Xinjiang, which indicates that in areas with significant human impacts, such as croplands and oases, net primary productivity (NPP) shows a marked response to non-climatic factors [38]. Furthermore, land-use conversions, such as the transformation of grasslands to croplands leading to a 94.64 gC/m\({}^{2}\) increase in NPP, clearly reflect that human regulation of moisture conditions can surpass natural climatic constraints, thereby potentially altering the apparent response of vegetation to metrics like PET [38]. This suggests that in oasis areas with stronger human intervention, PET reflects the unique mechanism by which vegetation regulates water use through evapotranspiration, rather than merely serving as a simple indicator of water stress. However, some regions within the basin (53.2% of the total area) showed no correlation between PET and NDVI. These regions represent natural ecosystems in the study area that are minimally or not at all influenced by anthropogenic water regulation. In such ecosystems, soil moisture is in a state of long-term depletion, with no regular irrigation to supplement it. Natural precipitation is scarce, evaporation is intense, and shallow groundwater is either too limited or too deep to be effectively utilized by shallow-rooted desert vegetation. Future research should further investigate the spatial heterogeneity of the PET-NDVI relationship across different regions and the underlying reasons to more accurately understand the response mechanisms of vegetation to water changes in arid areas. Thirdly, the significant contribution of human activities to vegetation restoration, such as the increase in NDVI in oasis areas, confirms the \"social-ecological coupling\" characteristics of ecosystems in arid regions [20]. For instance, [PERSON] et al. found that the expansion of farmland in Xinjiang is highly synchronized with the increase in NDVI [19]. This study further reveals, through spatial heterogeneity analysis, that the construction of shelterbels and irrigation projects are the core driving forces behind oasis vegetation improvement. However, ecological restoration and agricultural development overly dependent on groundwater, especially against the backdrop of a continuous rise in PET, may result in unsustainable water resource consumption. In the Turpan-Hami Basin, agricultural water use accounts for as much as 90% of the total. Should future climate change intensify the water supply-demand contradiction, the existing irrigation mode, which is heavily dependent on groundwater, will face significant challenges, and its long-term sustainability is questionable. The ecological risks arising therefrom need to be guarded against. It should be noted that this study has several limitations.