| Plants are the primary components of terrestrial ecosystems and play a critical role in mitigating climate change,regulating regional ecosystem functions,and carbon balance.Snow cover is a vital natural landscape and the most critical component of the frozen circle in the"Three Poles."Its effects on atmospheric circulation,land surface hydrological processes,and regional ecosystems are significant due to its high reflectivity,low thermal conductivity,and a range of thermodynamic,dynamic,and hydrological effects resulting from snow and snowmelt changes.The impact of snow cover on vegetation growth is a complex ecological hydrological process that is affected by multiple factors,including indirect effects,complex pathways formed by multiple factor couplings,and positive and negative feedback effects.The unique environment of the Qinghai-Tibet Plateau has turned it into a globally significant biodiversity conservation area and ecological security barrier.The ecological hydrological processes of plateau vegetation have unique characteristics,and the impact of snow cover changes on vegetation growth is of exceptional and significant importance.This paper aimed to clarify the impact of plateau snow cover changes on vegetation growth.Firstly,it analyzed the temporal and spatial trend of snow depth and NDVI to clarify the trend change situation.Secondly,it analyzed the time correlation between NDVI-snow cover changes and compared it with the correlation between temperature,precipitation,and solar radiation and vegetation to understand the characteristics of snow participation in vegetation ecological hydrological processes.Thirdly,it studied the spatial differences of multi-year correlation between snow cover and vegetation,distinguishing the spatial correlation differences between horizontal and vertical dimensions and different vegetation types to clarify the spatial heterogeneity of the impact of plateau snow cover changes on vegetation at different times.Fourthly,it constructed a set of seasonal lag test methods to understand the degree and spatial differences of NDVI’s response to snow cover changes on a seasonal basis.Finally,it explored the systemic impact mechanism of snow cover on vegetation ecological hydrological processes in the Qinghai-Tibet Plateau using the path analysis method.Based on the above analysis,it drew the following conclusions:(1)Over the past 40 years,various research factors on the Qinghai-Tibet Plateau have shown significant temporal and spatial trends.Snow depth has shown a widespread but less significant decreasing trend,with a multi-year rate of change of-0.016 mm/a,while NDVI has shown a large-scale significant increasing trend,with a rate of change of 0.0005/a.The trends in snow depth and NDVI exhibit certain spatial patterns in both horizontal and vertical gradients,with significant differences in different regions of the plateau,and with high-altitude areas exhibiting lower significance of change than low-altitude areas.Among meteorological factors,the average temperature has shown a significant increasing trend over many years,with a multi-year rate of change of 0.03℃/a,while overall precipitation has shown a non-significant increasing trend,with a multi-year rate of change of 0.30 mm/a.Solar radiation has exhibited a widespread and significant decreasing trend,with a multi-year rate of change of-0.11 W/m~2·10-a,and the changes in meteorological factors show significant spatial differences.(2)There exists a strong correlation between the snow-vegetation and climate-vegetation systems,which manifests as a lagging effect.Using a multi-factor correlation time-scale Pearson test,this study found that precipitation has the strongest positive correlation with NDVI,followed by snow depth,temperature,and solar radiation,respectively.NDVI shows a synchronous response to precipitation,temperature,and solar radiation,but a significant opposite response to snow depth,with an R value of-0.76,indicating that snow has a negative impact on vegetation growth.Moreover,the impact of snow on vegetation is more pronounced in high-altitude areas,where grasslands exhibit a significant negative correlation while deserts and forests display a positive correlation.Under the joint action of snow physical mechanisms and ecological responses,the highest snow depth corresponds to the lowest NDVI value with a 2-month lag,which results from the complex physical mechanism and ecological response process,and varies in different spatial contexts.Additionally,extreme snowfall events that lead to substantial increases in snow depth negatively impact NDVI for more than 3 years,with a significant annual lag effect.(3)Snow indirectly affects vegetation through its impact on soil,which plays a crucial role in the ecological and hydrological processes of vegetation on the plateau.The effect of snow on vegetation primarily operates through its influence on soil temperature and moisture,which in turn impacts vegetation growth.Snow has a positive effect on soil temperature and a positive but relatively weaker effect on soil moisture compared to temperature.Temperature has a significant direct impact on soil temperature,and its effect is stronger than that of snow depth on soil temperature.Although precipitation has a significant impact on soil moisture,its effect on NDVI also depends on the role of snow.Snow affects NDVI primarily through its impact on soil temperature.The quantity of snow is an essential factor that influences NDVI,and while its impact may not be as evident as temperature or precipitation,its significance should not be overlooked. |
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