# Spatiotemporal Variations in Vegetation Canopy Interception in China Based on a Revised Gash Model
## 1 Introduction
Numerous studies employed remote sensing to estimate the flux or reveal the dynamics of water [33; 34; 35], nutrients [36], and heat [37] in land surfaces, which turned this tool into a conventional but indispensable method in global hydrology research. In recent years, increasing attention has been paid to the application of remote sensing to measure canopy interception at a large scale. For instance, [PERSON] et al. [38] calculated the vegetation canopy interception of rainfall in southern China by combining observed rainfall data and leaf area index data obtained using a moderate resolution imaging spectroradiometer. [PERSON] et al. [31] utilized remote sensing data to forecast canopy interception from an empirical interception model in Europe, Africa, and South America. Nevertheless, the above-mentioned studies and a number of other relevant studies mainly inversed canopy interception from remote sensing data through simple regression relationships or empirical formulas. The integration of remote sensing data to a process-based canopy interception model from the perspective of the physical mechanism is still a key technical challenge at present [39]. Although few studies have attempted to use remote sensing data to run the revised Gash model [30; 32], the coupling of the remote sensing technique and process-based interception models is still at an early stage, due to the complexity of model parameters and the resolution of remote sensing products. Hence, there is an urgent need for more relevant studies, especially in regions with a wide range of vegetation types and high variability, as the model obtained from these areas have been shown to generally contain more uncertainties. China is a vast country with a wide range of vegetation types, including forests, shrubs, herbaceous vegetation, alpine tundra, marsh and aquatic vegetation, agricultural and desert vegetation [40]. Due to climate change and ecological conservation projects, vegetation growth significantly increased in most areas of China since the 21 st century [41], which contributed to a quarter of the global net increase in vegetation coverage with only 6.6% of the global vegetated area [42]. Specifically, the Loess Plateau China, where the Grain for Green Program is well established, has experienced a distinct increase vegetation coverage, with the NDVI growth rate reaching 0.008 yr\({}^{-1}\) during the 2000-2015 period [43]. The karst area in the Guangxi-Yunnan-Guizhou region in Southwestern China, another typical area chosen for ecological conservation projects, saw a stronger vegetation greening trend during the ecological protection period (2001-2016) than during the reference period (1982-2000), and this trend was influenced by eco-engineering [44]. Therefore, within the context of these vegetation changes, it is urgent to elucidate how canopy interception varied in different ecosystems in China during the last two decades in order to understand the ecohydrological effects of vegetation under the persistent impact of climate change and ecological engineering. The objectives of this study were to (1) develop and verify a large-scale revised Gash model running by satellite observation and meteorological data; (2) investigate the spatial and temporal variations of canopy interception in various vegetation types in China since the 21 st century; and (3) explore the main factors driving the variations of canopy interception in China.