warm front Boundary between an advancing warm air mass and the cooler one it is replacing. Because warm air is less dense than cool air, an advancing warm front rises over a mass of cool air. Compare cold front.

water pollution Any physical or chemical change in surface water or groundwater that can harm living organisms or make water unfit for certain uses.

water table Upper surface of the zone of saturation, in which all available pores in the soil and rock in the earth's crust are filled with water. 

waterlogging Saturation of soil with irrigation water or excessive precipitation so the water table rises close to the surface.

watershed Land area that delivers water, sediment, and dissolved substances via small streams to a major stream (river). Also drainage basin is used. 

watt Unit of power, or rate at which electrical work is done. See kilowatt.

weather Short-term changes in the temperature, barometric pressure, humidity, precipitation, sunshine, cloud cover, wind direction and speed, and other conditions in the troposphere at a given place and time. Compare climate. 

wetland Land covered all or part of the time with salt water or fresh water, excluding streams, lakes, and the open ocean. See coastal wetland, inland wetland. 

wild species Species found in the natural environment. Compare domesticated species. 

wilderness Area where the earth and its community of life have not been seriously disturbed  by humans and where humans are only temporary visitors.

wildlife All free, undomesticated species. Sometimes the term is used to describe only free, undomesticated animal species. 

wildlife management Manipulation of populations of wild species (especially game species) and their habitats for (1) human benefit, (2) the welfare of other species, and (3) the preservation of threatened and endangered wildlife species. 

wildlife resources Wildlife species that have actual or potential economic value to people.

wind farm Cluster of small to medium-sized wind turbines in a windy area to capture wind energy and convert it into electrical energy. 

windbreak Row of trees or hedges planted to partially block wind flow and reduce soil erosion on cultivated land.