冠层表面阻力与环境因子关系模型及其在蒸散估算中的应用

建立了一个华北平原冬小麦群体冠层表面阻力与环境因子关系的模型。根据该地区冬小麦生态系统的一组波文比-能量平衡观测资料,用非线性最优化方法模拟冠层表面阻力与太阳辐射、气温、空气饱和差和土壤含水量等环境因子的关系,得到模型四个参数的拟合值。用另外两组观测资料验证该模型的预测能力。结果表明,该模型能较好地模拟表面阻力,拟合度分别为0.93和0.67.将该模型应用到Penman-Monteith蒸散公式,发现蒸散的模拟值与实测值的拟合度达0.9以上,相对偏差小于5%.通过比较发现,该模型对蒸散的预测精度高于空气动力学方法。

A MODEL FOR THE RELATIONSHIP BETWEEN CANOPY SURFACE RESISTANCE AND ENVIRON MENTAL FACTORS AND ITS APPLICATION TO EVAPOTRANSPIRATION ESTIMATION

Surface resistance takes an important role in vegetation-atmosphere interaction. A model simulating the relationship between canopy surface resistance and environmental factors is established. According to one data set of Bowen ratio-energy balance above winter wheat canopy observed in 1992 in North China Plain, four parameters in the model are fitted by multi-variable nonlinear least-square optimum algorithm. The updated relationship between surface resistance and such environmental factors as solar radiation, air temperature, saturated vapour pressure deficit and soil moisture in root layer is obtained. The model is validated with other two data sets acquired in 1992 and 1995 for predicting canopy surface resistance. It is shown that the model is capable of modeling canopy surface resistance over the main growth stage of winter wheat with agreement index of 0.93 and 0.67, respectively. When the model is applied to Penman-Monteith formula, it is shown that the estimated evapotranspiration agrees well with that observed from field. The agreement index of evapotranspiration is over 0.90 and the mean bias is less than 5%. The evapotranspiration predicted by the model is closer to the observed with Bowen ratio-energy balance method than that by aerodynamics resistance method. The results of sensitivity analysis show that when four parameters change ±20%, the corresponding changes of evapotranspiration are different. The changes caused by the parameters related to saturated vapour pressure deficit and soil moisture are more obvious than those caused by the parameters related to solar radiation and air tempreture. Saturated vapour pressure deficit and soil moisture are shown the major factors affecting the evapotranspiration rate and canopy surface resistance. The influence of the parameters on evaporation depends on how much the environmental factors are.