# Water Use Efficiency Spatiotemporal Change and Its Driving Analysis on the Mongolian Plateau
## 1 Introduction
For example, changes in the vegetation growth season may affect the quality of vegetation growth and the carbon storage capacity, thus directly affecting the WUE [29]. At the same time, the degree of interpretation of GPP regarding WUE anomalies in InnerMongolia is higher than that for ET; however, the relationship between WUE anomalies and vegetation greenness and meteorological factor anomalies is still unclear [30]. Phenology refers to the study of natural events such as growth and reproduction in vegetation, animals, and other organisms, which may occur earlier or later in response to climate change. Rising temperatures often cause phenomena like vegetation blooming and animal activity to occur earlier, affecting ecosystems and agricultural production. Phenology changes are an important indicator of global warming, reflecting the impact of climate change on nature, and they have become a key metric in global climate monitoring [31; 32; 33; 34]. Most previous studies have shown that carbon storage is affected by the temperature and humidity [35; 36; 37; 38; 39]. Changes in vegetation phenology also affect carbon storage and sinks. For example, an earlier 'turning green' period may cause plant leaves to be larger, intercepting more light in the canopy, thereby improving the light efficiency and increasing the spring GPP and vegetation transpiration [40]. Some studies have shown that changes in the phenological parameters of vegetation affect carbon assimilation [41; 42; 43]. Thus, these parameters may be able to indicate the impact of vegetation changes on WUE. To explore the influence of phenological parameters on water use efficiency, we considered the effects of the vegetation phenology on both NPP and ET. In addition, due to the complexity of the ecosystem, the impact of changes in the growing season on WUE may not be consistent across different regions. Most previous studies on WUE in the Mongolian Plateau have focused on the relationship between WUE and meteorological factors over the past 20 years [30; 44]. Studies on WUE over long periods and trend analyses of various models are limited, and research on the synergistic effects of vegetation and meteorological factors and the impact of vegetation and climate anomalies on the WUE in the Mongolian Plateau is still insufficient. In addition, changes in vegetation phenology due to climate change may lead to changes in NPP and ET, indirectly affecting WUE. Thus, it is of great significance to study the impact of the vegetation phenology on WUE and the potential mechanisms underlying this impact. There are few studies on the restoration ability of an ecosystem's WUE that consider past anomalies and their resistance to abnormal changes in meteorological factors and vegetation greenness. In addition to natural factors, the effects of human interference on ecosystems should be considered. Studying the synergistic effects of meteorological factors and vegetation on the water use efficiency in the Mongolian Plateau is of great significance for a more comprehensive understanding of the mechanism of water use efficiency changes.