Urban Ecology - Ecological Systems - page 281

Examples such as these suggest a principle:
Principle 8 : Urban areas contain remnant or newly emerging vegetated and stream
patches that exhibit bioecological functions.
One of the fluxes that exercises the interest of urban planners and managers
worldwide is water. This concern extends well beyond those cities that are located
in arid or semiarid environments. Indeed, some cities, such as Phoenix, AZ, and Los
Angeles, CA, are so well connected to distant water supplies via diversions from the
Colorado River that they may seem impervious to drought. Ironically, although
arid-land cities do show concern for water, many cities from moist climates are
coming to acknowledge the sensitivity of their reservoir systems to periodic
drought [ 34 ]. New York City, with its system of impoundments more than
200 km to the north, or Boston with its reservoir in rural central Massachusetts
must now plan for the impacts of periodic drought and of the drying that may come
with climate change. Even now, development in some counties in eastern Maryland
faces limits due to shortages of groundwater, which are the sources for these
suburban-style developments.
Such concerns with water supply are not limited to the USA. Urbanization on the
Indian subcontinent is sensitive to projected reduced snowpack in the Himalaya
Mountains, in which its rivers originate. Water withdrawal for agriculture and
forestry in highlands of South Africa stands to alter water availability for which
lowland settlement and wildlife compete. Similar diversions along the tributaries of
the Nile are of concern for international relationships in East Africa.
Water supply is not the only aspect of water flux that is of concern. All cities, no
matter whether they are in moist or dry climates, must deal with periods of high
rainfall. Even desert cities are subject to occasional local thunderstorms, or to floods
from the foothills and mountains upstream. Hence, stormwater management in
spates is as of as much concern in Mediterranean Santiago, Chile, as it is in
temperate Seattle, Washington. The traditional mode of stormwater management
is to collect it and pass it off downstream as rapidly as possible. While this solves
local problems, it creates problems downstream. Stream bed erosion, scouring out
the habitats of aquatic organisms and the spawning grounds of anadromous fish, and
increasing the temperature of downstream reaches affected by runoff from hot
paved surfaces are some of the consequences to the engineering approach to
stormwater management. Many urban management plans now reference water
supply and stormwater management as key concerns.
A principle emerges from these sorts of events and situations:
Principle 9 : The flux of water, including both clean water supply and stormwater
management, is of concern to urbanizing areas worldwide, and connects them
explicitly to larger regions.
Ecologists and other biologists have recognized the presence of wildlife and
plants in cities for a long time. This tradition is especially strong in Europe, but also
has early roots in Japan and the USA. Interest has focused both on organisms that
represent the native biota and those that represent threats to either native biota or to
human health.