18 8Built systems, built areas, and whole regions
retain much of their rural appearance and culture, but almost all are near
the metropolitan area or a satellite city. Other than the normal agricultural
activities, effects of these towns on natural systems and human uses are usually
limited. Towns near borders between cropland and natural land are discussed
below.[A14]Most urban regions have no towns in natural areas, and hardly any region has
>25 % there(Figure7. 13).Within natural landscapes and large natural patches, towns commonly have
significant negative impacts on natural systems, including water, soil, and
wildlife. Analogous negative impacts also occur on human land uses, such as
recreation and water supply, that depend on intact natural systems. Fortunately
urban regions have few towns in natural areas. Limiting growth of the existing
ones is a valuable investment.[A15]Towns near borders of agricultural and natural areas are widespread, i.e., present
in >75 % of the regions(Figure7. 13).Towns near the boundary between agricultural and natural areas are well
located, because they displace little valuable land and their outward impacts are
mainly on the edges of the natural and cropland areas. This pattern is consistent
with the aggregate-with-outliers model for optimally meshing different land uses
in a landscape (Forman1995,Forman and Collinge1996). If villages are to grow
into towns in a region, limiting the growth of villages in natural areas, plus
encouraging it in those near the border of agricultural and natural land, is a
priority.‘‘ Natural” disasters
[A16]Many regions are susceptible to a ‘ ‘ natural” disaster that affects a major
portion of the metropolitan area, with f lood hazard being the problem in about half of
the cases(Figure7. 9).Although appropriate data on this important subject were difficult to find
and interpret, it appears that metropolitan areas could be called hazardous
places due to their location and their concentration of people and structures.
Flooding from an old dam that fails or bombing by warplanes would be human-
caused disasters. Natural disasters are earthquakes (e.g., Kobe, Japan), debris-
flows from volcanic eruptions (Perera, Colombia), and hurricanes/cyclones (Dar-
win, Australia). Yet natural disturbances may become ‘‘disasters” due in major
part to human activities. Thus high levees holding back a huge lake broke in a
2005 hurricane to cause widespread inundation of the adjacent lower-elevation