The urban environment: Evaluation of hydrological changes and their consequences

Urban population growth has been an uninterrupted and accelerating phenomenon throughout this century. By the year 2000 almost 50% (2850 million) of the world's people will have become urban dwellers. Urbanization has profound impacts on the hydrological cycle, at varying scales. Many cities are situated on aquifers whose abundant, but fragile, groundwater resources are being rapidly degraded by inadequately controlled exploitation and indiscriminate effluent and waste disposal practices. This degradation is a contributory cause of increasing water resource scarcity, escalating water supply costs and growing health hazards. More emphasis is beginning to be placed on understanding these hydrological changes and on proactive management of the urban hydrological cycle. However, many of the changes are not capable of direct measurement and are difficult to quantify. In principle, some can be addressed through the use of isotope techniques with the prospect of providing unique data sets. Such applications are reviewed in the light of the limited published data. (author)