Water vapor is continuously evaporated from the earth's land and water surfaces. Water present in soils is extracted by plants through transpiration and results in the release of water vapor into the atmosphere. The combined process is called evapotranspiration. Regional and global variation in evapotranspiration have an affect on the environment that directly impacts people, e.g. climate change, agricultural productivity, the water budget of semi-arid regions, and the rate of increase in pathogens and insect populations.