| Soil moisture is a key parameter in land surface energy balance and water circulation.Understanding its temporal and spatial changes has very important guiding significance in monitoring drought,analyzing physiological and ecological of vegetation,managing water resources and researching climate changes in regional scale.According to the strong temporal and spatial heterogeneity,traditional observations at ground station of soil moisture obviously cannot meet the regional scale research and application.The development of remote sensing technology provides an opportunity for large area inversion of soil moisture,and is considered to be the only feasible way to obtain the spatial and temporal distribution of global soil moisture.Microwave has become the most commonly method for obtaining soil moisture on a regional or global scale due to its unique advantages such as all-weather,penetrability and unaffected by clouds and rain.However,most microwave soil moisture products have lower spatial resolution(-25km)which cannot satisfy actual demand of soil moisture in watershed or field-scale agriculture,ecology,and hydrology.Currently,an effective method to obtain soil moisture with high-resolution is downscaling microwave soil moisture products.The Tibet Plateau is known as the"Asian Water Tower".By researching the regional temporal and spatial distribution and analyzing the response characteristics climate change has important scientific significance for exploring the energy balance and water cycle of the Qinghai-Tibet Plateau.This study first downscaling the coarse resolution microwave soil moisture to obtain long-term soil moisture in Tibet Plateau area,secondly,the downscaled soil moisture have been verified by using in-situ soil moisture data.On this basis,the spatial and temporal distribution characteristics of soil moisture in Qinghai-Tibet Plateau and its spatial and temporal response to climate change were analyzed.The main findings include:1)physical downscaling method based on soil evaporation efficiency can obtain high precision soil moisture data in Tibet Plateau,which provides reliable data for spatial and temporal variation analysis of kilometer scale.Compare with in-situ soil moisture data,the root mean square error is 0.094 m3/m3,the correlation coefficient is 0.941;(2)Overall,from 2007 to 2017,the average annual soil moisture in most areas of the Tibet Plateau remains stable,the annual change is about-0.003 m~3/m~3-0.004m~3/m~3.The soil moisture in the northern and partial semi-arid regions of the Tibet Plateau has a significant upward trend,while the soil moisture in the southwest margin of the Tibet Plateau has a significant downward trend;(3)the eastern part of the arid region and the central and southern part of the semi-arid region,Soil moisture is mainly affected by temperature.And in the western arid,semi-arid and humid regions,Soil moisture is mainly controlled by precipitation. |
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