基于VIC模型模拟的干旱区土壤水分及其时空变化特征

Spatio⁃temporal variation of soil moisture in arid area based on VIC land surface model

土壤水分在陆地水循环中起着十分重要的作用,大尺度、长时间及高精度的土壤水分监测是旱情预警、生态恢复与精准农业决策部署的重要指导依据,而陆面过程模式模拟在时空尺度上可获得更准确的土壤水分特征。以渭⁃库绿洲为目标靶区,结合VIC陆面过程模型和土地利用类型变化,探讨2009—2016年研究区年际间不同地类土壤水分时空变化规律,并用实测数据进行精度验证,结果表明:(1)东北区域土壤含水率模拟值较高,土壤含水量低值集中在研究区西部与南部区域。(2)盐渍土壤表层含水量高于耕地,每年雨季,灌丛土壤含水量高于其他3种地类,由于大量荒地转为耕地,绿洲荒地土壤含水量与耕地土壤相互接近,在28.784—53.741 mm之间。(3)渭⁃库绿洲近7年耕地与盐渍地面积大幅度增加,耕地与盐渍地面积增幅达35%以上,荒地面积相较2009年减少约46%,灌丛面积增幅约15%。(4)荒地土壤含水量伴随面积大幅度下降,土壤含水量数值集中在正态曲线28.6 mm以上区域。VIC模拟值与实测值均方根误差(RMSE)范围在1.4—2.80之间,RE范围在0.90—2.20之间,R2范围在0.40—0.60之间,模拟效果较好。

There is an increasing need of large⁃scale,long⁃term and high⁃precision soil moisture monitoring.Methods based on land use features,such as Variable Infiltration Capacity(VIC)land⁃surface process model,can obtain more accurate soil moisture characteristics in the spatio⁃temporal scale.It is of great significance to drought early warning,ecological restoration,and precision agriculture decision⁃making and deployment.This paper took Wei⁃Ku oasis as the target area,combined with VIC land surface process model and land use type change,to discuss the temporal and spatial changes of soil moisture of different types in the study area from 2009 to 2016,and verified the accuracy with the measured data.The results showed that:(1)the simulated value of soil moisture content in the northeast region was high,while the low value of soil moisture content was concentrated in the western and southern regions of the study area.(2)The surface moisture content of saline soil was higher than that of cultivated land.In rainy season,the soil moisture content of shrub soil was higher than that of other 3 types of land.Due to a large number of wasteland being converted into cultivated land,the soil moisture content of oasis wasteland was close to that of the cultivated land,between 28.784 and 53.741 mm.(3)In the past 7 years,the area of cultivated land and salinized land in Wei⁃Ku oasis have been greatly increased,the area of cultivated land and salinized land increased by over 35%,the area of wasteland decreased by about 46%compared with that of 2009,and the area of shrub increased by about 15%.(4)The wasteland soil moisture content decreased significantly with the area,and the soil moisture content values were concentrated in the area above 28.6 mm of the normal curve.The VIC simulated value and measured value RMSE ranged from 1.4 to 2.80,RE ranged from 0.90 to 2.20,R2 ranged from 0.40 to 0.60,and the simulation effect was good.