Water is central to survival—without it, plant and animal life would be impossible. Water is a central component of Earth’s ecosystems, providing important controls on the weather and climate. Water is likewise central to economic well being via delivery of direct precipitation and agricultural irrigation, forestry, navigation, waste processing, and hydroelectricity. There are more than 250 international river basins, and in each basin, water moving across diplomatic boundaries can create sensitive and potentially dangerous political challenges. Our present understanding of climate and the consequences of future climate change (whether natural or anthropogenic), together with population growth and economic development, necessitate that water resources are of increasing interest and importance for the foreseeable future.
Reflecting the impacts of population growth alone, water use is increasing everywhere. If per capita consumption of water resources continues to rise at its current rate, humans could be using over 90% of all available freshwater by the year 2025, leaving just 10% for all other living organisms. This forecast does nothing to reflect the high likelihood of climate change. Many studies point to serious consequences for water resources due to climate change, especially in arid regions. For instance, with a moderate 1º C to 2º C increase in the mean annual air temperature and a 10% decrease in precipitation, a 40 to 70% reduction in annual runoff can be expected in regions that already experience insufficient moisture. The same is true for water resources of large economic regions. American scientists have calculated that with a 2º C climate warming and a 10% reduction in precipitation, a 1.5- to 2.0-fold decrease in water resources is possible for those regions of the country located in arid climate zones alone.
It is well-known that the severity of water management problems is determined by the ratio of available water resources to demand. With predicted future climate changes, plans for further development in irrigated agriculture, reservoir construction, and most water-consuming types of industry will have to be revised. All such revisions will need to result in the greatest positive impacts being felt in hot arid regions. These regions already have difficulties with water supplies and undergo persistent conflicts between different water suppliers and consumers. Regardless, as water use responds to changing demand with some degree of inertia, regional water availability will be determined primarily by the changing water regime within a given territory. The water management systems of river basins will be complex and will have to be extremely flexible and capable of efficient control over water resources under different climate scenarios. In this respect, the regions with large capabilities in river runoff regulation, as is the case in many parts of the United States of America, Canada, and Europe, will have considerable advantages to solving water supply and flood regulation relative to those regions with more natural river systems such as regions located in southern and south-eastern Asia and South America.
Relatively little account has been taken of the qualitative or quantitative depletion of water resources due to increasing pollution of natural fresh water sources. On this basis alone, all water resource estimates may be optimistic. The major sources of intensive pollution of waterways and water bodies are found in the forms of contaminated industrial and municipal wastewater as well as water runoff originating from irrigated areas. This problem can be no more acute than it is in the industrially developed and densely populated regions where relatively little wastewater purification processes take place. It is estimated that in 1995 the volume of wastewater was 326 km3/year in Europe, 431 km3/year in North America, 590 km3/year in Asia and 55 km3/year in Africa. Many countries discharge large portions of their wastewater containing harmful substances into the hydrological system with no preliminary purification. Prime water resources are thus polluted and their subsequent use becomes unsuitable, especially as potable supplies. Every cubic meter of contaminated wastewater discharged into water bodies and watercourses can potentially spoil between eight and ten cubic meters of pure water. This means that most parts of the world are already facing the threat of catastrophic depletion of water resources due to pollution alone.
Forecasts of future population, industry, and power-generation growth are used to predict water withdrawal and water availability. The values obtained for 2025 are ±10-15% for those regions containing predominantly developed countries and ±20-25% for the regions with predominantly developing countries. To be able to plan and properly manage for these potential future demands for fresh water, it will be vital to achieve close cooperation between scientists and water resource managers. Scientists will have to collaborate from different countries and international organizations and deal with many problems related to hydrology, climatology, and other related disciplines in a cooperative effort to better understand the complex use and protection of water resources.
In human history, water has been central to society and remains so today. Over time, we have grown more aware of the correlations between accelerated growth of industry and population and the increased uses of water and how that use relates to the Earth’s fixed supply. In recent times, it has become more clear that human prosperity and prospects for survival vary with the amount and distribution of fresh, unpolluted water. Each year there are millions more humans, but no more water than before. The same amount of water exists now as when the Earth was formed. Ultimately, although finite in quantity, water is a renewable resource. Nonetheless, there can be little argument that exponential population growth coupled with an increasing demand for fresh water is resulting in increasing pressures on this valuable resource. The continued degradation, abuse, and pollution of the environment and its resources, may cause irremediable damage to our own health and that of the planet on which all life depends. Despite strong feedback mechanisms between hydrological and meteorological processes, which have historically lead to poor representations of hydrological processes, increased understanding will lead to improved management strategies for the future and the various processes of the hydrological cycle.
Ward, A. D. and W. J. Elliot. 1995. Editors. Environmental Hydrology. Lewis Publishers, CRC Press, Florida, p. 9.