A stochastic optimization approach for integrated urban water resource planning

Urban Multi-Source Water Supply in China: Variation Tendency, Modeling Methods and Challenges

Urban water resources are the basis for the formation and development of cities and the source of urban water supply. However, with the acceleration of urbanization and the explosion of urban populations, the contradiction between water supply and demand in some areas, especially in big cities, has become increasingly prominent. It is simply not sufficient to rely on local conventional water resources to meet urban water demand, and a single source water supply mode has a higher vulnerability, resulting in greater safety risks in urban or regional water supply systems. Therefore, giving full play to the water supply capacity and carrying out multi-source water supplies are necessary and urgent. This paper gives an overview of the optimal allocation of multi-source for urban water supply concerning variation tendency, modeling methods and facing challenges. Based on the variation tendency of water consumption and water supply pattern in China, Tianjin is taken as a typical city for systematically outlining water supply changes and cause analysis. Subsequently, the modeling methods for proposing the optimal allocation scheme are summarized, which are composed of defining the topological relation, constructing the mathematical model and seeking the optimal solution. Ultimately, the current and emerging challenges are discussed including emergency operation of multi-source water supply and joint operation of water quality and quantity. These summaries and prospects provide a valuable reference for giving full play to the multi-source water supply capacity and carrying out relevant research so as to propose the optimal allocation scheme in urban multi-source water supply systems.

Assessment of the municipal water cycle in China

Water produced from municipal utilities accounts for nearly 10% of the sum water demand in China. The municipal water cycle that integrates processes of urban water supply, water use, sewage treatment, and water reclamation has been assessed for 655 cities across nine drainage areas in mainland China in 2012. These cities in total extracted 55km³ raw water for municipal use from surface waterbodies and ground aquifers, approximate to the countrywide freshwater extraction of Russia or Italy. After purification and transmission, 45km³ water was distributed to industrial, service, and domestic users. 36km³ of post-use sewage was collected and environmentally safely treated; merely 3.2km³ of the treated water was reclaimed. Driven by increasing urbanization, the municipal water demand in cities of China may grow 70% by 2030. The Hai River and the Huai River basins, which harbor 137 cities and occupy a majority of the densely populated North China Plain, are most exposed to physical water scarcity. The municipal water abstraction in these cities can remain constant by promoting demand-side and process conservation in the next two decades. Interbasin transfer and unconventional sources will provide municipal water double than the cities' need. Whereas the urban water security can be technically enhanced, the challenges are to better improve water use efficiency and mitigate economic and environmental costs of the municipal system.