2008), there does appear to be a broad tendency for urban densities to decline in all parts of the world however urban is defined (Angel et al., 2011). This is only in part because urban advantages can now be achieved at lower densities. In recent decades, urban environmentalists as well as public health experts have tended to favour more compact cities (Frumkin, Frank, and Jackson, 2004; Jenks and Burgess, 2000; Van der Waals 2000) pursued through “Smart Growth” (Filion, 2010) or more effective urban planning (Dulal, Brodnig, and Onoriose, 2011). According to their proponents, compact cities build over less land, require shorter trip distances, increase the share of pedestrian, bicycle and public transport trips, and provide a better basis for cogeneration and other low-carbon measures. Compact urban development can also be designed to interweave densely settled urban land with green spaces, enabling urban dwellers to tap local ecosystem services. Neither “compact” nor “sprawl” are well-defined concepts (Frenkel and Ashkenazi, 2008), and environmental burdens take a wide variety of forms, making it difficult to demonstrate empirically that compact cities are environmentally preferable (Batty, 2008; Vella and Morad, 2011). The serious challenge to the compact city concept as a means of mitigating climate change comes from the claim that policies designed to promote more compact cities may nevertheless increase carbon emissions indirectly. Measures designed to increase density in one city may inadvertently—or under pressure from vested interests—have side-effects that increase emissions in that city or increase carbon emissions elsewhere. For example, it has been argued that policies promoting compactness may favour inefficient mono-centric cities, and that, if such measures are to reduce carbon emissions, they may need to be supplemented by others to decentralize jobs and create poly-centric cities (Gaigné, Riou, and Thisse, 2010). It has also been argued that in the United States land use regulations in compact lowcarbon cities have been pushing development to sprawling high-carbon cities (Glaeser and Kahn, 2010). Despite such arguments, it is widely accepted that, at least within the existing range of densities, more densely settled cities are likely to emit less carbon than otherwise comparable low-density cities. Concentrated settlements also create opportunities for increasing resilience to climate change. Even when density is not adaptive in itself, concentrating people and activities in particular locations may be so, particularly if protective area-specific measures are taken. Thinking back to the issues of water-short cities and coastal cities threatened with flooding, the challenges are quite different, but similar patterns emerge. In drylands, as elsewhere, water resources are distributed unevenly, and some locations will be closer than others to more ample water supplies. It is also generally more economical to distribute water to a few concentrations of urban population than to a large number of scattered rural settlements. Similarly, intra-settlement water distribution tends to be less costly in dense rather than in sprawling cities and less costly in urban than rural areas. Of course, if lower costs translate into lower prices, this will also result in higher demand. Thus, urbanization can help reduce the burden of increasing water scarcity, but requires more water resource management, both on the supply and the demand side. 34
The De mogra ph y of Ada ptation to C l imate Ch ange
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