基于替代模型的非点源污染模拟不确定性分析——以石头口门水库汇水流域为例

Uncertainty analysis of non-point source pollution simulation based on surrogate model——case study for Shitoukoumen Reservoir Catchment Basin

为分析机理模型参数不确定性对非点源污染模拟结果的影响,以石头口门水库汇水流域为研究区,选择采用SWAT模型对研究区非点源污染进行模拟,并应用蒙特卡罗(Monte Carlo)方法对非点源污染机理模拟模型参数进行不确定性分析.但蒙特卡罗方法需要大量的取样并多次运行模拟模型,若直接调用SWAT模型,耗费的时间和资源较多.为降低计算负荷,应用克里格方法建立研究区非点源污染机理模型的替代模型,而实现蒙特卡罗模拟.结果表明:采用克里格方法建立研究区非点源污染SWAT模型的替代模型,不仅可以大幅减小计算负荷,还可以保持较好的精度;在置信水平为90%时,氨氮负荷输出和总磷负荷输出的区间范围分别为0.98×10~3~1.67×10~3t/a,0.29×10~3~0.84×103~t/a;相比于非点源总磷的输出结果,非点源氨氮输出结果的不确定性较大.

Shitoukoumen Reservoir Catchment Basin was selected as a study area to analyze the influence of the model parameters uncertainty on the simulation results of non-point source pollution.A non-point source pollution simulation model was established by SWAT combining Monte Carlo methods,which was applied to analyze the uncertainty of the parameters of non-point source pollution mechanism model.However,it is time consuming if SWAT model is called directly during the model running process.Therefore,a surrogate model was established to replace SWAT model by Kriging method.The results showed that the surrogate model could not only reduce the computation load,but also demonstrate an ideal accuracy.It was found that the output of ammonia nitrogen(NH3-N)and total phosphorus(TP)ranged from0.98×103to1.67×103t/a and from0.29×103to0.84×103t/a at a confidence level of90%,and the output of NH3-N showed the greater uncertainty compared with that of TP.