1.1 General
Evaporation is the process by which water is converted into gaseous state and is returned to the atmosphere as vapour. Evaporation is an important process in the hydrologic cycle preceding precipitation. It is the process by which water in the liquid form transforms into vapour through the transfer of energy. When water is converted from solid state to vapour state without passing through liquid state then it is called sublimation. In the atmosphere, evaporation occurs from the water surface of natural and artificial reservoirs, lakes etc., and snow and soil surfaces and also from the surfaces of vegetation. As such a part of the precipitation reaching the earth’s surface is lost through evaporation. The rate of evaporation is dependent on (I) the vapour pressures at the water surface and air above (II) air and water temperature, (III) wind velocity, (IV) Atmospheric Pressure, (V) quality of water and (VI) Size of water body.
Dalton’s law of evaporation: - John Dalton was the first scientist to describe the process of evaporation, scientifically. An evaporation rate varies directly with difference of vapour pressure air and water. Evaporation (E) = C (ew-ea) Where, E = evaporation rate in mm per day …show more content…
Water evaporates from a variety of surfaces, such as lakes, rivers, soils and wet vegetation. Energy is required to change the state of the molecules of water from liquid to vapour. Direct solar radiation and, to a lesser extent, the extensive temperature of the air provide this energy. The driving force to remove water vapour from the evaporating surface is the difference between the water vapour pressure at the evaporating surface and that of the surrounding atmosphere. As evaporation proceeds, the surrounding air becomes gradually saturated and the process will slow down and might stop if the water air is not transferred to the
Evaporation is the process by which water is converted into gaseous state and is returned to the atmosphere as vapour. Evaporation is an important process in the hydrologic cycle preceding precipitation. It is the process by which water in the liquid form transforms into vapour through the transfer of energy. When water is converted from solid state to vapour state without passing through liquid state then it is called sublimation. In the atmosphere, evaporation occurs from the water surface of natural and artificial reservoirs, lakes etc., and snow and soil surfaces and also from the surfaces of vegetation. As such a part of the precipitation reaching the earth’s surface is lost through evaporation. The rate of evaporation is dependent on (I) the vapour pressures at the water surface and air above (II) air and water temperature, (III) wind velocity, (IV) Atmospheric Pressure, (V) quality of water and (VI) Size of water body.
Dalton’s law of evaporation: - John Dalton was the first scientist to describe the process of evaporation, scientifically. An evaporation rate varies directly with difference of vapour pressure air and water. Evaporation (E) = C (ew-ea) Where, E = evaporation rate in mm per day …show more content…
Water evaporates from a variety of surfaces, such as lakes, rivers, soils and wet vegetation. Energy is required to change the state of the molecules of water from liquid to vapour. Direct solar radiation and, to a lesser extent, the extensive temperature of the air provide this energy. The driving force to remove water vapour from the evaporating surface is the difference between the water vapour pressure at the evaporating surface and that of the surrounding atmosphere. As evaporation proceeds, the surrounding air becomes gradually saturated and the process will slow down and might stop if the water air is not transferred to the