The amount of evaporation, the process of water changing from liquid or solid state to gaseous state and escaping into the atmosphere is called evaporation. Evaporation is the amount of water dispersed into the air by evaporation in a certain period of time, usually expressed in millimeters of the thickness of the evaporated water layer, the evaporation of water surface or soil water, respectively, measured by different evaporators.

Generally the higher the temperature, the lower the humidity, the greater the wind speed, the lower the air pressure, the greater the evaporation; vice versa, the smaller the evaporation. Soil evaporation and water surface evaporation measurement, in agricultural production and hydrological work is very important. In areas where rainfall is scarce, groundwater sources and inflow of runoff are not much, such as evaporation is very large, that is, prone to drought.

The main factors affecting evaporation

1. Related to the high or low temperature. The higher the temperature, the faster the evaporation. No matter what temperature, there are always some molecules in the liquid with great speed can fly out of the liquid surface and become vapor molecules, so the liquid can evaporate at any temperature. If the temperature of the liquid increases, the average kinetic energy of the molecules increases, the number of molecules flying out from the liquid surface will increase, so the higher the temperature of the liquid, the faster the evaporation.

2. If the surface area of the liquid increases, the number of molecules in the vicinity of the liquid surface increases. Thus, in the same time, the number of molecules flying out from the liquid surface increases, so evaporation is accelerated by an increase in the surface area of the liquid.

3. When the vapor molecules flying into the air collide with air molecules or other vapor molecules.

Evaporation is an integral part of the surface heat balance and water balance, and one of the most directly affected by land use and climate change in the water cycle, as well as an important factor in the exchange of heat energy.

Therefore, evaporation has important application value in estimating terrestrial evaporation, crop water demand and crop water balance. It is very important to conduct the study of evaporation changes to gain a deeper understanding of climate change and explore the law of water cycle changes.

In practical terms, it is important to guide the design of water conservancy projects, soil improvement in agriculture, forestry and animal husbandry, soil moisture regulation, irrigation quota development, as well as the study of water resources and the development of climate zoning. At this time the evaporation sensor plays an important role.