时域组合模型与西安市城区地下水污染预测

基于系统层次性的分解与综合,将区域环境质量的时间序列变化概括为趋势项、周期项和随机项,提出了用于环境预测的时域组合模型及其检验方法;以20年来西安市地下水污染预测为例,在电子表格软件Lotus1-2-3forWindows的支持下,完成了西安市地下水总固体、总硬度、硝酸盐、氯化物、氟化物、六价铬6种污染及样本超标率、平均污染指数和超标区面积3个指标的数学建模。该方法事物变化规律清晰,预测精度远高于传统方法,同时也为西安市地下水污染的预测防治提供了科学依据。

Time domain combined model and groundwater pollution forecast in Xi'an City

With the accumulation of monitoring data,the study of region environment has turned from static distribution to dynamic time change.And the relationship between environment quality and economic development is known in the course of dynamic variation.On decompounds and integration of system hierarchy,the time serial changes of environment qualities in a region is divided into tendency,cycles and occasional ones in this paper.The tendency one could be simulated with easy function such as polynomial,exponential,logarithms function.The cycle one could be simulated with triangle function,occasional one could be simulated with ARMA(p,r)or AR(p).A time domain combined model and its verification method with correlation coefficient R,Post-test error ratio C and Probability of small error P are put forward.The R,C and P tests from different aspects constitute a full test system.This makes the model credible.This paper takes the ground water pollution in Xi'an City for 20 years as an example,on the support of Lotus 1-2-3 for Windows,the 18 time domain combined models are established about 6 pollutants by 3 indexes of groundwater pollution in Xi'an for 20 years,the 6 pollutants include total solid,total rigidity,nitrate,chloride,fluoride,and hexavalent chromium,the 3 indexes are exceed standard rate,average pollution index and the area of exceed standard.In this methodology it combined 3 time serial changes,and the reason of this division is analyzed:the tendency one reflects the rule of environment change with economic change,the cycle one is related to economic cycle and law-enforcing,the occasional one is caused by stochastic factors.The results are as follows:the tendency reflects that the pollution becomes low with the economic development.The cycle reflects that law-enforcing is sometimes rigorous and sometimes slack,the cycle is about 9-10 years.The simulation of occasional one is in accordance with the rule that the future is the same as the past,the back is more accurate.So it is adopted as a associative method about quality and quantity.The results of simulation model to R,C,P test are very good,the rules of changes are clear and the forecasting precision is higher than that of the traditional methods.In the same time,this paper has offered scientific basis for forecasting and controlling groundwater pollution in Xi'an City.