ABSTRACT
Cities are where people have most transformed nature, replacing vegetation with roofed and paved surfaces, burying stream channels, creating indoor climates, and making huge artificial transfers of energy water and materials. Expanding cities transform hydrological relationships, changing the magnitude and frequency of flooding. Rising land prices often mean that homes are built on relatively unstable slopes or on the floodplains of rivers. The poor, especially in dense squatter settlements in third world cities, often have no choice but to occupy hazardous sites on steep slopes, close to rivers, or near polluting factories. All too often, their settlements are vulnerable to road collapse, water pipe breakages and sewer failures and to floods, landslides or subsidence.
