Water in urbanregions 163The loss of vegetation protecting a water-supply drainage basin also increases
thecost of water. Indeed, a sharp rise in cost may occur when vegetation cover
drops to some 70 % (Peter Kareiva, personal communication).
[W14]The few cities with water supply from stream or groundwater have considerable
built area in the general drainage area of the water supply(Color Figures2--39).
Tegucigalpa apparently largely uses streamwater (supplemented by some lake-
water),while apparently Bamako and Abeche mainly use large numbers of
groundwater wells to provide water supply for the city population. Spreading
development around the somewhat-fragile streams poses a severe threat for
erosion/sedimentation, chemical pollution, and water loss. Avoiding additional
development in the general drainage area is important. In the case of extracting
groundwater close to the city, urban pollutants of numerous types can readily
percolate into the groundwater. Neither case is stable. Achieving viable water-
supply alternatives for a future larger city is ahigh priority.
[W15]Forty percent of the cities has an adjacent water supply, and a sixth of the cities
has a distant water supply(Figure6.15).
In the former case, adjacent relatively high-density development plus air pol-
lution degrades the water supply. In addition, urbanization, both densification
and outward spread, occur around the water supply, worsening the problem.
Establishing alternative water supplies at a distance is ahigh priority(Color
Figure9).
Cities with a distant water supply have little urbanization or air pollu-
tion threat. However, they have a higher maintenance and water-transport
cost. Perhaps more importantly, the city must usually depend on other polit-
ical/administrative units to adequately protect the drainage basin. Establish-
ing strong long-term land protection measures with dependable policing is
important.
Thus 37 ‘‘major” patterns and results focused on nature, food, and water
have emerged from analyzing the urban regions (Color Figures2--39). Useful
guidelines and priorities doubtless apply widely for other cities worldwide. The
next chapter continues this analysis by focusing on built systems and built areas.