While many previous studies have looked at the worldwide changes and impacts of climate change and related variability on water resources, few have focused on an assessment of the specific effects and needed adaptation and mitigation for water systems in cities across the globe. The Intergovernmental Panel on Climate Change (IPCC) report on the water sector (IPCC, 2008) summarizes links between climate change and water through all of the physical elements of the terrestrial hydrologic cycle, ocean components, linkages to water supply, and global effects, but does not focus specifically on urban water systems. Similarly, the ADAPT Project (Aerts and Droogers, 2004) looked at adaptation for regional water management in seven typical watersheds across the world. However, most of this study was focused on surface water resources and their impacts on agriculture, food supply, energy production, and flood hazards, or on other impacts including groundwater resources, but did not focus on cities. There is thus an urgent need for a focused overview of the water supply and wastewater treatment sector in urban areas.
The range of challenges related to climate change and cities in regard to the water supply and wastewater treatment sector is very great, depending on geography, economics, administrative capacity, and demography. Many of the challenges are general, and some are more specific to particular cities. Accordingly, this chapter includes capsule descriptions of water supply and wastewater treatment in four cities that illustrate a variety of situations in which adaptation to climate change will be needed.