北京城市生态占水研究

Ecological water depletion by human use in Beijing City

在前人研究的基础上,提出了生态占水的概念及计算方法,构建了生态占水驱动因素分析模型,计算各因素对生态占水变动的贡献率,并采用灰色关联分析法对生态占水-水生态因子进行关联分析。以北京市为例计算1999—2009年的生态占水量,结果显示水量型占水和水质型占水均呈现波动式逐年下降趋势,分别由1999年的25.56亿m3和12.55亿m3减少到2009年的15.65亿m3和4.58亿m3;2003—2005年北京市生态占水率明显高于其它时期,达到80%以上,2006年以后逐步下降,但仍然高于50%;水量型占水是过去10 a中最主要的占水类型。生态占水驱动因素分析结果得出,1999—2009年的总体变动中人均消费水平的提高是促使北京市生态占水增加的关键驱动因素,其次是第二产业增加值。占水-水生态因子关联分析显示,地表取水和污水处理率两个因素与水生境因子的变化有着较强的关联性;退水和地下取水与水环境因子有较强的关联性,地下水埋深和人口两大因素与水安全有着较强的关联性。

A concept of ecological water depletion by human use（EWD） and its calculating methods were studied in this paper.EWD was defined as the volume of water in natural ecosystem used by human beings,and this indicator could be applied to study the relationship between ecological water-use and human water use.EWD includes internal-EWD and external-EWD,which was classified by the studied scales.If EWD was classified by style,it includes resource-based one and quality-based one.The model for EWD drivers′ analysis was applied to calculate the contribution ratio of different factors such as consumption per capita,industry value added,agriculture value added and so on,and determine the key driver factor.Moreover,grey relational analysis（GRA） was applied to estimate the relationship between EWD and ecological factor of water（EFW）. EWD concepts and calculating methods were applied to the case of Beijing City.Main results were： 1） from1999 to 2009,resource-based EWD declined from 25.56×108 m^3 to 15.65×108 m^3 and quality-based EWD declined from 12.55×108 m^3 to 4.58×108 m^3.The ratio of total ecological water depletion（Rewd） was over 55% in 2009,which had been even higher than 80% during 2003—2005.Comparing resource-based and quality-based EWD,the former was more important.Through analyzing drivers of EWD,it is found that the level of consumption per capita was the most important driver factor for EWD increasing and industrial added value was the second.There are some changes of EFW in Beijing City caused by EWD including： 1） Groundwater.Compared with 1960s,the groundwater storage of Beijing decreased by more than 100×10^8 m^3 in 2009;2） Wetlands.The area of wetlands in Beijing was 2461 km2 one hundred years ago,but nowadays only remained 514km2 in 2007;3） Water quality.More than 40% rivers could not reaching the national water environmental quality standards;4） Biodiversity.Wetlands birds are now only 152 species comparing with more than 300 species in historical records;5） Safety.The area of land subsidence caused by groundwater overdraft had reached 4114km2 in 2005.It has been found that in Beijing the factors of surface water use and sewage treatment rate have strong correlation to water habitats with correlation degree（r） 0.642 and 0.600 respectively;the factors of water withdrawal and groundwater use are strongly related to water environment with r 0.839 and 0.821 respectively;the depth of groundwater and population have strong correlation to water disaster with r 0.887 and 0.733 respectively. To enhance the ecological services of water,the rate of ecological water depletion（Rewd） accounting should be reduced to 30% by means of strictly controlling the withdrawal of surface and groundwater,increasing the sewage treatment rate,recharging groundwater and strictly controlling population growth as well.It is necessary to adjust the industrial structure,enhance the efficiency of industrial water use,increase the rate of industrial water recycling,and improve the efficiency of farming irrigation water use to reduce the EWD by human use in Beijing effectively.People′s behavior and consciousness on water consumption were very important for constructing the water saving society.