Estimation of Rootzone Soil Moisture over the Qinghai-Xizang Plateau using the Exponential Filter Model
High-precision and long time-series soil moisture(SM)data are crucial for quantifying the land-atmo-sphere interactions on the Qinghai-Xizang Plateau(QXP).However,most of current studies on the Tibetan Pla-teau mainly focus on retrieving surface SM based on the satellite data,with relative lack of studies on estimating rootzone SM(RZSM).Based on data collected from five SM observation networks on the QXP(i.e.,Shiquan-he,Pali,Naqu,upper reaches of Heihe River,and Maqu),this paper systematically evaluates the applicability of the exponential filter model for estimating RZSM(i.e.,10,20,40 cm)in different climatic and land areas of the QXP.In addition,we explore the impacts of different environmental factors(e.g.,soil properties,cli-mate,and vegetation)on the estimated key model parameter,i.e.,characteristic time length T.Moreover,the reliability of regional-scale T-value obtained using three methods(i.e.,using the median value of optimal T-value obtained for each observation network or the whole Qinghai-Xizang Plateau,or the random forest model)for estimating RZSM on the QXP was assessed.The results showed that:(1)With the increase of soil depth,the correlation between rootzone and surface SM decreased while its spatial heterogeneity increased.This results in a decrease in the accuracy of the exponential filter model,but the obtained T-value and its spatial heterogeneity in-creased.(2)Spatially,with the increase of precipitation and SM content,the correlation between rootzone and surface SM increased while its spatial heterogeneity decreased.This leads to an increase in the accuracy of the ex-ponential filter model,while the difference in accuracy of the model applied to different sites shows a decreasing trend.(3)Soil properties,especially the sand content,are the main factors controlling the spatial distribution of T-value on the QXP.(4)The different methods for obtaining regional-scale T-value have little influence on the ac-curacy of the exponential filter model in estimating the RZSM on the QXP.Specifically,both the commonly used methods,such as using the median value of optimal T-value or the random forest model,can obtain reason-able regional-scale T-value and achieve consistent and accurate RZSM estimations.These findings are expected to promote the use of the exponential filter model to accurately obtain the RZSM on the TP using satellite-based surface SM data.
exponential filter modelQinghai-Xizang Plateau(QXP)rootzone soil moisturedifferent climat-ic and land areas
万方数据
维普
