Study On Spatiotemporal Variation And Ecological Effects Of Soil Moisture In The Three River Headwaters Region Base On Multi-source Data

The Three River Headwaters Region(TRHR)is located in the hinterland of the Qinghai-Tibet Plateau(TP),and it is the largest nature reserve in China.The natural environment of the TRHR is harsh and is characterized by a single ecosystem structure,slow energy conversion process,weak ecological carrying capacity,and weak selfrecovery ability.The TRHR is fragile and very sensitive to climate change.Soil moisture is an important parameter in the exchange of hydrothermal energy between land and atmosphere,and it is an essential component of the water cycle in the land ecosystem.Under the influence of global warming,it is of great significance to reveal the change law of soil moisture in the TRHR by analyzing the relationship between soil moisture and meteorological factors and studying the ecological effect of soil moisture in order to maintain the function and stability of the ecosystem.Based on soil moisture data of SMOS satellite and SMAP satellite,ERA-interim reanalysis dataset,GIMMS-NDVI data,meteorological station data as well,this paper adopted the methods of moving average,inverse distance weight method,and multiple linear regression to(1)evaluate the applicability of SMOS soil moisture data and ERAinterim reanalysis dataset(2)analyze the change characteristics of soil moisture and its influencing factors,(3)establish the Vegetation Health Index(VHI)model,and(4)analyze the changing law of VHI in the TRHR.The results showed that:(1)The soil moisture data of SMOS in the TRHR is basically consistent with the ground monitoring data from April to October,and its value is slightly lower than the ground monitoring data;the soil moisture monitoring from the ascent of SMOS satellite is generally higher than that from the descent.(2)The soil moisture in the TRHR in summer is higher than that in spring,and the average soil moisture in summer is 0.12m3/m3 higher than that in spring,Further,the spatial distribution of soil moisture in spring and summer is significantly different;(3)In terms of space,the spatial distribution of soil moisture in the TRHR is significantly different,with obvious changes,On the whole,the soil moisture increased gradually from northwest to southeast.The soil moisture in the source region of Lantsang river is generally higher than that in the source region of Yellow river,followed by the source region of Yangtze river.(4)Soil moisture is correlated with precipitation,evaporation,temperature,wind speed,vegetation cover,human activities and other factors.Soil moisture is significantly positively correlated with precipitation,and negatively correlated with evaporation and temperature.When only statistically analysis of precipitation,evaporation and temperature,the contribution ratio of the three factors to soil moisture is 61%,26%,13%.Each source region is slightly different,in the source region of the Yellow river,the contribution ratio of precipitation,evaporation and temperature to soil moisture is 39%,43%,18%;in the source region of the Yangtze river,it is 52%,31%,17%;in the source region of the Lantsang river is 38%,47%,15%.It can be seen that precipitation is a key factor affecting soil moisture.(5)There is a significant positive correlation between soil moisture and NDVI,the spatial distribution of NDVI and soil moisture is consistent.The higher the vegetation coverage,the higher the inversion soil moisture,which also reflects the regulation effect of soil moisture on vegetation and its health status.(6)According to the data from 2010 to 2015,the calculation results base on the data from 2010 to 2015 shows that VHI in the TRHR is stable on the whole,which is high in the south and low in the north.The VHI in the source area of the Lantsang river is higher than that in the source area of the Yellow river,and the VHI in the source region of the Yellow river is higher than that in the source region of the Yangtze river.VHI is certain correlated with terrain.(7)Statistically,the health status of vegetation in the TRHR is good,among which the health status of vegetation in the source area of the Lantsang River is favorable,the health status of vegetation in the source area of the Yellow river and Yangtze river is general good.There are significant regional characteristics in the distribution of soil moisture and the ecological environment in the TRHR.VHI is closely correlated with precipitation,evaporation,etc.In recent years,the precipitation and evaporation is increasing,The health status of vegetation is generally favorable and getting better,with poor health status in local area.It shows that the ecological environment protection measures play a role in TRHR,the overall improvement trend is mainly due to global temperature rise and increased precipitation.Limited to ground monitoring data,it is suggested to strengthen the integration of sky and earth the synchronous monitoring of multiple spatial and temporal scales.Human life should be properly controlled,at the same time,Strengthening the water conservation,increasing precipitation,improving surface soil moisture and the vegetation health in local area in the TRHR.