Foundmantal Study On Ecological City Water Security In The Northwest China

Northwest cities are facing a common problem of arid climate and rare rainfall with uneven spatial and temporal distribution, which lead to a shortage of water resources.The large number of water requirements for urban ecological environment construction could intensify the conflict between water supply and demand in urban area.In this study,it is of significance for the sustainable development of eco-city in northwest district to research foundmantal issues corresponding water security.The study starts from the water problems occuring in Baoji city and the expending aspects,the main contents and results are as follows:(1)Proceeded from the meaning of ecological city,the characteristics of the water using system and water restraints in eco-city are analyzed. Combining with increasingly abundant points of city water security,the aspects on the city water security system are discussed.(2)The characteristics of rainfall system in the Baoji city are studied, the results indicate that annual rain days has a descending tendency,the linear dependence of the rain days and the precipitation is significant. The detrend fluctuation analysis method is used to obtain that the Long-range dependence of the rainfall time series behaves differ on different study scales.The annual precipitation will be decreasing in near future, the precipitation has features of multi-stages and mutation, the drought frequence was increased after 1990, and relaxed after 2000,when a sudden change occurred,but still be in a low level.Based on the drought forcasting model,the drought events in the future are approached.(3)Based on higher-order statistical theory,the non-linear feature of the river runoff series in Baoji city are identified,then the trend, persistence,fractal and chaotic are analyzed thoroghly to illustrate that the runoff systems of the Wei River,the Qian River and the QingJiang River all have fractal structures and chaotic characteristics.The annual runoff of the three rivers all appear downtrend,which have a strong persistence.(4)The copula theory is applied to construct the joint distribution of annual runoff in the Wei River and the Qian River, which is the largest tributary of the Wei River in Baoji City,the synchronous-asynchronous encounter probability of rich-pool runoff is analyzed.The results show that the probabilities of rich, moderate and pool flow year of the Wei River and the Qian River, occurring at the same time are 0.72,0.45 and 0.21 respectively,when the Wei River is in moderate flow year, the probability of the Qian River in rich and pool flow year are 0.5 and 0.248, when the Qian River is in pool flow year, the probability of the Wei River in rich flow year is 0.25.(5) The structural changes of water supply and water saving in Baoji city are studied to make clear that the present water supply structure is single,which is mainly relying on conventional water resources,while the development and utilization of non-conventional water resources and water saving have certain potential.(6) For the eco-city water system complexity, the city water demand forecasting methods are carried out.The grey theory and self-memorization principle are combined to establish the forecasting water consumption volume based on gray GM(1,N) self-memory model.On the base of industrial structure and its gross domestic product of Baoji city,a corresponding water demand prediction model of extensive matter element is created. The method of structure analysis and blind number theory were combined to forecast city water consumption volume considering uncertainty.(7) The significance of the eco-city river ecological water demand is discussed,the method to determine the river ecological water demand in Northwest territories is concerned.Calculations show that 3.2079 hundreds million ecological water is needed for the Wei River in Baoji urban area to ensure its vitality when taking full account of urban sewage treatment developing capacity.(8) The meaning and characteristics of recycled water and rainwater resources in the city are analyzed, ecological water support capacity provided by developing urban sewage treatment capacity is expounded,the potential of rainwater resources in the urban district are estimated,the potential demand in urban district for non-conventional water resources is calculated quantitativly.(9) Water safety and security strategies for sustainable development of Baoji city is putforward, which means the construction of water-saving city is a matter of great urgency,needs the rational and efficient use of conventional and non-conventional water resources planned as a whole to protect the healthy development of the eco-city.