土壤风蚀影响因子参数化

Soil wind erosion area in northern China covers many land use types, soil types and vegetation types, so that the existing soil wind erosion models for cultivated land cannot meet the demands in scientific study and wind erosion control practice. Parameterization of the factors influencing soil wind erosion, including soil antierodibility factors, wind erosivity factors and roughness interference factors is the key to establish a soil erosion model with thorough dynamic basis and wide applicability. To accomplish the parameterization, this program will carry out the following work. i) Establishment of the spatial databases based on the previous researches by former scientists and our pre-researches, including land-use database, soil database regarding to the types and physicochemical properties, vegetation characteristic database, and DEM topographic maps. Typical study areas for measurement and sampling and conditions for experiment and simulation will be determined then. ii) Measurement of aerodynamic roughness length in different circumstances, including bare soil surface, soil surface covered with different vegetation or gravels of different size and density, cultivated soil with different tillage measures, and meso- or micro-scale topographies in the typical study areas. iii) Calculation of the threshold velocities and drag for bare soil surface, soil surface covered with different soil crusts and soil surface with different roughness elements. Drag partition on soil surface with different roughness elements will also be calculated. This work will be based on the results of wind tunnel simulation and field measurements. iv) Exploration of the quantitative relations between soil antierodibility and grain size composition, moisture content, content of calcium carbonate(CaCO3) and organic material, bulk density and vegetation root density in surface soils, etc. v) Generalization and parameterization of soil antierodibility factors, wind erosivity factors and roughness interference factors according to the dynamic principles of wind erosion.

中国北方土壤风蚀区包括多种土地利用、土壤和植被类型，现有耕地风蚀模型不能满足需要。本项目在前人和项目组预研究成果基础上，建立研究区土地利用类型、土壤类型及其理化特性、植被特征、DEM地形图等空间数据库，确定典型观测区、样品采集区和实验模拟条件；野外测量典型观测区的裸露、有不同特征植被、不同耕作措施耕地、不同大小和密度的砾石覆盖、中小尺度地形等情形下的空气动力学粗糙度；根据模拟实验和野外观测数据，计算典型土壤类型裸土和结皮条件下的临界摩阻风速和剪应力，不同粗糙元条件下的临界摩阻风速和剪应力，以及粗糙元及其之间裸土表面的剪应力分离；研究土壤抗蚀性与表土机械组分和水分、碳酸钙和有机质含量、表土容重、植物根系等之间的定量关系。依据风蚀动力学原理，分别对地表粗糙干扰因子、风力侵蚀因子、土壤抗蚀性因子进行归并，并将其参数化，为未来构建具备风蚀动力学理论基础和具有广泛适用性的土壤风蚀模型奠定理论基础。

土壤风蚀研究的目标，是在厘清影响因子对土壤风蚀影响的基础上，建立预测模型并用于指导生产实践。目前只有适用于美国中西部大平原耕地的WEPS和RWEQ经验模型相对成熟，还没有针对土壤风蚀发生范围更广泛的草地、草灌地、耕地、流沙地等土地利用类型的风蚀模型。为了克服经验模型中影响因子分类混乱和缺乏风蚀动力学理论基础的不足，本项目依据影响因子的力学属性，对其重新归类，划分为风力侵蚀因子、地表粗糙干扰因子、土壤抗蚀性因子三类，并将这三类因子参数化，为未来构建具备风蚀动力学理论基础和具有广泛适用性的土壤风蚀模型奠定理论基础。取得的主要成果包括：（1）在研究区内，取得了比预期更丰富的基础数据。计算和制作了表土粒径分布、有机质和碳酸钙含量、地表砾石覆盖、空气动力学粗糙度栅格图，近15年（2001-2015）16天一次植被覆盖度和表土含水率栅格图，近37年（1980-2016）风速、风向、空气密度、降水量、积雪、地温（0cm）栅格图，栅格图均为250m×250m分辨率，1:25万DEM图；修正了1:10万土地利用类型图；确定了12种植被类型；研究了上述影响要素的时空变化及其对土壤风蚀的影响。（2）开展了56种土壤和5个植被覆盖度等级、8个植株形态和密度、25个土垄尺寸和间距、25个砾石大小和密度、6个孔隙率沙障（作物留茬）等实验研究，在1030组风洞实验数据和50多组野外实地观测数据支持下，建立了典型粗糙因子对风动力干扰作用的参数化表达式。（3）构建了新的风侵蚀力（WDF）模型，计算了近37年（1980-2016）内各月的WDF、风蚀气候因子WF（RWEQ中的表达风、降水、积雪等气候因子对土壤风蚀影响的关键参数）和输沙势，比较分析结果表明，新构建的WDF模型更适用于表达风作用于土壤表面的侵蚀力。（4）在3260组风洞实验数据和7191个表土原状土样品抗剪强度数据支持下，建立了土壤理化特性、植物根系密度与抗剪强度的定量关系，初步实现了表土抗蚀性因子参数化。完成了任务书规定的研究任务，部分研究内容超过预期，为下一步建立通用风蚀模型奠定了理论基础。