Water resources prospects from a hydrological sciences perspective

Full text: The 21st Century has started with a rapidly rising demand for water, an increasing toll of death and destruction from floods and droughts and a mounting burden of water pollution. These and a host of other problems provide overwhelming evidence that the world's water resources are subject to intensifying pressures and growing constraints. They highlight the vital need for water resources to be carefully husbanded and protected in order to ensure the future of modern civilisation and the integrity of the natural environment. Distributed unevenly in both space and time across the globe by the hydrological cycle, the world's water resources are stored and moved as a gas, a liquid and as a solid, above, on and below the ground surface. The quantity of these resources is usually the attribute of prime concern, however in many situations their quality, both chemical and biological, is even more important or as equally important. The river basin and the aquifer define the spatial limits of water resources, while their dimensions in time can range from seconds to the century and far longer. Hydrology is the science which deals with the water resources of planet earth and, most recently with those of other bodies in the solar system. In particular it provides the scientific basis for their assessment, development and management. Indeed over the last 300 years or so, the application of the principles of hydrology has been essential to socio-economic development. These same principles must be used now to promote sustainable development and to avoid the world water crisis which a number of authorities consider will arise later this Century. While attempts to assess water resources may have started in ancient Egypt and in early China, little progress seems to have been made until Perrault carried out a hydrological study in the basin of the Seine in the 17th Century. His results and those of Marriote showed conclusively from observations that the rainfall over the basin was more than sufficient to produce river flow. Their findings overturned the long-held theory that rivers rise from subterranean springs fed from an internal hydrological cycle. With the series of advances in the last century and this, the present day practice of water resources assessment has progressed far from those rudimentary techniques employed in the Seine. But in the last 10 to 15 years they have also needed to account for possible climate change, as well as a host of other complications stemming from factors such as land use change and the volume and variety of pollutants being introduced into the aquatic environment. Ideally they would always be employed as a lead into the development and management of water resources, but this is often not the case. The planning, design and construction of water supply schemes, those for the generation of power, irrigation projects, flood mitigation works and the like need such assessments. The same methodology employed in real time is important to forecasting systems for floods and droughts. (author)