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  Glossary

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W

Water- A mineral composed of two parts hydrogen to one part oxygen with a unique combination of properties: liquid at room temperature, requires large amounts of energy for conversion from liquid to vapor and from solid to liquid, resistant to temperature changes, strong attraction between its own and other molecules, dissolves many substances, transmits visible light but absorbs thermal radiation.

Water “savings” - The amount of water that remains for additional use after technological manipulation of the hydrological cycle. Technologies include evapotranspiration suppression, reduced agricultural withdrawals, and decreased infiltration and deep percolation. A water “savings” can only be defined in the context of the water balance of a particular site and is largely an economic, not a hydrologic, concept. Hydrologically, water cannot be “saved” or “lost”. It can only be transferred from one place or phase of the hydrologic cycle to another.

Water scarcity - Condition in which the annual availability of renewable fresh water is 1 000 cubic meters or less per person in the population.

Water stress - Condition in which the annual availability of renewable fresh water is less than 1667 and greater than 1000 cubic meters per person in the population.

Water supply - The stream-flow volume that would occur at the outflow point of each sub-region if consumption were eliminated, ground water overdrafting were discontinued, and current water transfer and reservoir practices were continued.

Water table - The upper surface of the zone of ground water.

Water use, Consumptive - Water withdrawal and use in such a way that it is no longer available for additional uses – e.g., due to evaporation, transpiration, and ingestion by animals.

Water use, Non-consumptive - Withdrawal and use that return water to supplies for additional use – e.g., irrigation “return flows”, hydroelectric energy generation, and in stream-flow requirements.

Water withdrawal - Removal of water from any natural source or reservoir – such as lake, stream or aquifer – for human use. If not consumed, the water may later be returned to the same or another natural reservoir.

Wetlands - Land or areas (as tidal flats or swamps) containing much soil moisture. It is transitional between aquatic and terrestrial ecosystems and is covered with water for at least part of the year.

Wide-spectrum pesticide - A pesticide that kills a variety of organisms in addition to the pest against which it is used. Most pesticides are wide-spectrum pesticides. Compare narrow-spectrum pesticides.