根系层储水量对随机腾发响应特性的初步分析

Theoretical analysis of stochastic response of soil water storageto evapotranspiration flutuation

将潜在腾发量分成趋势分量与随机分量两部分，且假定该随机分量标准化后为正态白噪声过程，结合水量平衡方程推导出根系层储水量满足的随机微分方程．利用随机微分方程理论分析了土壤根系层系统中系统状态变量一根系层储水量对随机输入的响应特性，包括变量的转移概率密度、均值和标准差．

Based on the assumption that potential evapotranspiration consist of two part,of which one follows a deterministic seasonal trend and another fluctuates randomly around the former,and the water balance equation governing the soil water movement in the root zone,a conceptual stochastic model is established.The model is a stochastic differential equation.The corresponding Fokker Planck equation is derived on the basis of further assumption that the normalized random term of evapotranspiration follows the white noise process.The numerical solution of Fokker Planck equation is obtained and the mean and deviation process of state variables are tested with the field experimental data.The comparisons show that:1.The established model is valid and can be used to predict the soil water storage in root zone,2.The prediction deviation of SWS increases with time which may bring some difficulties for the accurate long lead time prediction of SWS.Finally,it iis suggested that the colored noise process of the random term of evapotranspiration must be taken into account in the model so that the prediction deviation of SWS could be reduced.