| In Soil,soil water content is very important properties,and also plays an important basic information in many fields such as hydrology,climate and agriculture.Soil water content directly affects the growth and development of plants and plays an important role in regulating natural ecosystems and agricultural production.The "One River and Two Streams" region is an important grain production base and sand control area in Tibet,and soil water content is a key factor for crop growth and one of the core factors to maintain the regional fragile ecological environment.Mastering the spatial and temporal distribution characteristics of regional soil water content is helpful for rationally regulating soil conditions,stabilizing agricultural production,and promoting the improvement of the ecological environment.This study based on MODIS remote sensing images,and uses the Temperature Vegetation Drought Index（TVDI）method combined with the measured soil water content data to invert the soil water content in the "One River and Two Streams" area from 2000 to 2020.On this basis,the spatial pattern characteristics and changing process of regional soil water content were analyzed,and the effects of temperature and precipitation on soil water content were explored.The results show:（1）Based on the MOD13A1 and MOD11A2 data of MODIS data products,the soil water content retrieved by the Vegetation Drought Index（TVDI）method is in good agreement with the measured soil water content data.The linear correlation coefficient R2 reaches 0.5268,and the mean relative deviation is 5.64%,indicating that the use of TVDI method to invert the soil water content in the "One River and Two Streams " area has high reliability.（2）The multi-year average soil volumetric water content in "One River and Two Streams" area is 7.96 % with a coefficient of variation of 0.13.In terms of spatial distribution,the study area as a whole exhibits a higher soil water content in the eastern region than in the western region,with the highest average soil water content of 9.31 %in Gongga County and the lowest average soil water content of 7.14 % in Lazi County.The average soil water content of the whole region is gradually increasing with the rise of altitude,but there is no obvious variation in different slopes and slopes aspects.In different soil types and different land use practices,the annual average soil water content varies significantly.In terms of land use methods,it shows that grassland >forest land > unused land > cultivated land,and in terms of soil types,it shows that the highest water content in the alpine steppe soil and the lowest in the tidal soil.（3）From 2000 to 2020,the average soil water content in the "One River and Two Streams" area showed an overall fluctuating upward trend with an increase rate of0.02 %/a.Among them,the area north of the Yarlung Zangbo River in the western part of the study area increased the most,while most of the areas south of the Yarlung Zangbo River in the western part of the study area did not change significantly,and the area on both sides of the Yarlung Zangbo River in the east had a significant decrease in soil water content.From the perspective of different seasons,the annual average soil water content showed summer>autumn>spring>winter.During the 21 years,the increase of soil water content in summer was the largest,followed by autumn,and the change of soil water content in winter and spring was not obvious.（4）The correlation between Soil water content and temperature is higher in the "One River and Two Streams" region,followed by precipitation,and varies significantly among different soil types.Soil water content increases with the increase of temperature,and also tends to increase with increasing precipitation. |
