On Transpiration and Soil Moisture Content Sensitivity to Soil Hydrophysical Data

Sensitivity of evapotranspiration E and root zone soil moisture content θ to the parameterization of soil water retention Ψ(θ) and soil water conductivity K(Ψ), as well as to the definition of field capacity soil moisture content, is investigated by comparing Psi1-PMSURF and Theta-PMSURF models. The core of PMSURF (Penman–Monteith Surface Fluxes) consists of a 3-layer soil moisture prediction module based on Richard’s equation in combination with the Penman–Monteith concept for estimating turbulent heat fluxes. Psi1- PMSURF and Theta-PMSURF differ only in the parameterization of the moisture availability function F_ma. In Psi1,F_ma is parameterized by using Ψ(θ) and K(Ψ) hydrophysical functions; in Theta, F_ma is parameterized by using hydrophysical parameters: the field capacity θ_f and wilting point θ_w soil moisture contents. Both Psi1 and Theta are based on using soil hydrophysical data, that is, there is no conceptual difference between them in the parameterization of E even if in Psi1F_ma depends on 12 parameters, while in Theta only on two soil/vegetation parameters. Sensitivity tests are performed using the Cabauw dataset. Three soil datasets are used: the vG (van Genuchten), CH/vG (Clapp and Hornberger/van Genuchten) and CH/PILPS (Clapp and Hornberger/Project for Intercomparison of Land-surface Parameterization Schemes) datasets. The vG dataset is used in van Genuchten’s parameterization, while in Clapp and Hornberger’s the CH/vG and CH/PILPS datasets are used. It is found that the consistency of soil hydrophysical data in the simulation of transpiration is quite important. The annual sum of E obtained by Psi1E^Psi1, differs from the annual sum of E obtained by Theta, E^Theta, because of the inconsistency between the fitting parameters of Ψ(θ) and K(Ψ) and the θ_f, and not because of the differencies in the parameterization of F_ma. Further, θ_f can be estimated not only on the basis of using soil hydrophysical functions (the θ_f so obtained is θ^Soil_f) but also on the basis of analysing the transpiration process (the θ_fso obtained is θ^tr_f). θ^tr_f values estimated from the condition E^Theta ≈ E^Psi1 are in acceptable accordance with the θ^Soil_f values proposed by Wösten and co-workers. The results are useful in optimizing the parameterization of transpiration in land-surface schemes.     

STUDY ON THE DYNAMIC PROCESS OF RILL EROSION OF LOESS SLOPE SURFACE

1 mTRODUCTIONAs a woridwide concem, excessive water erosion induces land degradation, causes losses of plantnutrients, and Ieads to off site enVironmental problems such as sedimentahon streams and reservoirs. mllerosion, which results from concentraed flow in a lindted and confined space, plays imPortant roles inthe erosion systCm on uPland areas. Data listed in Table l show its contribution and imPoftance to thetOtal slope soil losses. In the last decades, stodies on the physical mecha…     

黑河地区土壤及小麦体内水分动态观测分析

研究了甘肃黑河地区麦田土壤水分的变化动态。对春小麦同部位叶片及不同土壤分析的叶水势、气孔导度和蒸腾强度的日变化规律进行了观测和分析。对春小麦叶鞘、叶片和茎水势的变化民政部进行了比较。分析了土壤水分对叶水势、气孔导度和蒸腾强度的影响。建立了相对应的函数关系。     

SEDIMENT DAMAGES AND RECENT TRENDS IN THE UNITED STATES

lINTRODUCTIONWeoftenhavethepercepti0nthatsedimentisthebr0wnishoryell0wishcoloringinrunoffwater,thatlooksunpleasant,buteventually"g0esaway,"downstream,unseen.Butsedimentisn0tonlyaestheticallyunpleasant,itisalsoacarrierofpotentialchemicalc0ntaminants,fillsupwaterb0dies,andcausesphysicaldamaget0farmland,wildlife,andwatertreatmentsystemsandpowergenefat0rs.ThepurposeofthispaPeristoprovidean0verallperspectiveonthemagnitudeandtrendsofsedimelltasap0llutritintheUnitedStates.2CURRENTKNOWLEDG…     

土壤水分常数测定之我见

通过对土壤容重、田间持水量、凋萎湿度测定方法的研究，提出了土壤水分常数测定规范中存在和应注意的问题，以利做好当前的土壤水分常数测定工作。     

淮河流域冬春季土壤温湿度异常对夏季降水的影响及其应用的研究

夏季降水异常与前期环流、下垫面异常有密切的关系 ,文中重点研究了淮河流域前期下垫土壤温、湿度异常对夏季降水的影响。提出了一种动力与统计相结合寻找影响降水的因子的方法 ,通过将大气中的热量、水汽收支方程与一个简化的两层土壤温度、湿度方程相结合 ,并依据月尺度大气环流的演变特征 ,推导出月降水距平与 5 0 0hPa月平均高度距平场、土壤深浅两层温、湿度的关系 ;并利用台站观测资料 ,使用统计反演方法确定方程中各项的系数和量级 ,从而找出影响降水的主要土壤温、湿度因子 ;利用统计方法建立这些因子与淮河流域夏季降水异常之间的简单线性预报方程 ,并对 1982～ 2 0 0 0年淮河流域夏季降水趋势进行回报 ,结果表明 :对淮河流域夏季降水趋势的预测有很好的效果 ,且更加明确了土壤温、湿度因子与降水异常之间的动力学联系。     

原子荧光光度法测定土壤样品中砷的不确定度评定

通过原子荧光光度法对土壤样品中砷重复测定6次，计算实验标准差，同时对测试过程系统效应产生的不确定度分量进行评估，从而评定其不确定度。     

Quantitative estimation of skin soil moisture with the Special Sensor Microwave/Imager

A physically based retrieval scheme is described toinfer near surface moisture content of bare soilpatches from time series of the Special SensorMicrowave/Imager (SSM/I) Polarisation DifferenceTemperature (PDT) at 19.35 GHz. The PDT is modelled asa function of soil moisture using Fresnel's relationsfor specular reflection at the air-soil boundary,together with a dielectric mixing model for themoisture-dependent soil dielectric constant. Theproblem of the specification of parameters describingatmospheric and soil roughness effects is avoided byconsidering temporal variations of the PDT. Theretrieval method is applied to the FIFE site for atwo-week period in summer, during which heavy rainfalloccurred on a dry upper soil. Although differences insensing depths made a rigorous validation impossible,remotely sensed soil moisture showed a high degree ofconsistency with ground measurements. An erroranalysis shows that the method is capable of providingan accuracy of approximately 20% of moisture contentat field capacity. Finally, it is demonstrated thatthe method is relatively insensitive to soil texturalcharacteristics when moisture content is scaled withfield capacity.     

不同土壤水分和不同覆盖条件下麦田水分动态和增产机理研究

1997年 1月至 1 998年 6月在郑州水分试验场进行了小麦田覆盖期、覆盖量和土壤水分处理试验 .结果表明 ,覆盖是一种行之有效的保墒增产措施 .不同覆盖期、不同覆盖量和不同土壤水分对小麦干物重、叶面积、蒸腾强度、产量和水分利用效率有着显著的影响 .覆盖期、覆盖量和土壤水分含量的最佳结合点为 :冬前小麦停止生长之日、55%～ 70 %土壤相对湿度、450 0～ 60 0 0 kg/ hm2覆盖量 .在此状况下 ,产量可增加 1 8.5% ,水分利用效率提高 2 2 .1 % .     

Understanding the effect of a static driving shear stress on the liquefaction resistance of medium dense granular soils

The influence of a driving static shear stress on the liquefaction resistance of medium dense granular soils is investigated. A laboratory study of the behavior of five sands (percentage of silt varying between 2 and 42%, and D₅₀ varying between 0.55 and 0.09 mm) was undertaken. These five sands were sampled from the foundations of two dams in Quebec (Canada). Sixty cyclic direct simple shear (DSS) tests were performed with and without a driving static shear stress. Relative densities D_r varied between 60 and 70%, and static shear stress ratios =τ_st/σ′_vc varied between 0.2 and 0.6. The presence of static shear stress increased the cyclic strength of these soils. A relation between and K() factor giving the effect of preshearing on cyclic shear resistance is obtained. The mechanical competence is examined as a function of D₅₀ and percentage of fines. The observed dilatancy yielded rather cyclic mobility than liquefaction.