基于SiB2模型的土壤水分降尺度指标的适用性研究

Applicability Research of Indices in Soil Moisture Downscaling based on SiB2 Simulation

土壤水分是地表过程的核心变量之一,强烈影响着陆表—植被—大气间的能量和水分交换。当前基于星载被动微波遥感的土壤水分产品的空间分辨率普遍较粗(25~40km),无法满足流域尺度水文气象、生态水文模拟及水资源管理等研究和应用的需求,而土壤水分降尺度是目前较为可行的解决方案之一。通过对不同降尺度指标的研究,分析确定每种降尺度指标的适用条件,为土壤水分的降尺度研究奠定基础。利用2013年5月1日~9月30日黑河中游人工绿洲试验区大满超级站的气象数据驱动SiB2模型,分别模拟了土壤水分、土壤表层温度、植被冠层温度以及地表蒸散发、土壤蒸发等变量,利用Penman-Monteith公式计算了地表潜在蒸散发;利用SiB2模拟结果与P-M公式计算结果估算获得常用的土壤水分降尺度指标:表观热惯量(ATI)、土壤蒸发(E)、土壤蒸发/实际蒸散发(E/ETa)、蒸发比(EF)、实际蒸发比(AEF)。通过对降尺度指标与土壤水分之间相关性分析可知,在植被的整个生长季,5种指标与土壤水分之间都具有较好的相关性。其中ATI、E、E/ETa以及EF这4种指标与土壤水分之间的相关性都随着土壤深度的增加而逐渐减弱;而AEF与植被根区土壤水分的相关性最好,更能反映根区土壤水分的动态变化。从可决系数来看,各降尺度指标与土壤水分的相关性排序如下:2cm:E/ETa>EF>E>AEF>ATI;10cm:AEF>EF>E/ETa>E>ATI;80cm:EF>AEF>E/ETa>E>ATI。

Soil moisture is a key component of soil,which seriously affects energy exchange and water cycle of the soil-vegetation-atmosphere.The spatial resolution of current soil moisture products generally coarser（25～40km）,which cannot meet the watershed scale hydrologic meteorological,hydrological simulation and water resource management,but soil moisture downscaling is a currently feasible solution to application requirements.This paper based on the research of different downscaling indices to determine the applicable conditions of each indices and lay a foundation for downscaling study of soil moisture.This paper attempts to use SiB2 to simulate the soil moisture,soil surface/canopy temperature,evaporation and evapotranspiration,and based on Penman-Monteith formula to calculate potential evapotranspiration and to calculate various indices：Apparent Thermal Inertia（ATI）,Evaporation（E）,Evaporation/Evapotranspiration（E/ETa）,Evaporative Fraction（EF）and Actual Evaporative Fraction（AEF）.Analysis shows that the indices are all have a higher correlation with soil moisture but the ATI,E,E/ETa and EF with the increase of soil depth gradually weakened and the AEF have a higher correlation with root zone soil moisture.