Evaporation

EVAPORATION - is the process that converts water into water vapor. The vapor is further diffused into the atmosphere. In this way water is lost from the surface, no matter whether it is from open water (lakes, rivers) or from soil. It is important that evaporation moves water directly from the surface to the atmosphere, because the part of water that enters the atmosphere from the soil through the plants is called transpiration.

There is a number of climatic factors that affect evaporation. Most of them are quite obvious from our everyday experience. We know that after getting wet we will dry up faster if we stay in the sun, and it will be even faster on a windy day. When it is humid outside things do not seem to dry up as quick as when it is dry. So the evporation is higher when it is sunny, hot, windy and dry. Humidity, wind and temperature are usually available from standard metheorologic records. In many cases you can find metheorologic data for your area at the National Climatic Data Center (NCDC). Going to this site you can choose a state, then find a station that is located close enough to the site you are modeling and then find most of the cliamtic data needed to model evaporation. Most problematic is to get data on solar radiation. For some reason it is not part of standard observations and direct measurements are rare. This is why LHEM has several modules that can be used to estimate solar radiation based on other climatic conditions and the latitude of the site.

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