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 m³ to 15.65×10⁸ m³ and quality-based EWD declined from 12.55×10⁸ m³ to 4.58×10⁸ m³. The ratio of total ecological water depletion (R_ewd) 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 100×10⁸ m³ 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 (R_ewd) 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.