Evaporation and Evapotranspiration

Evaporation and Evapotranspiration

• Evaporation is the process where a liquid transforms into a gas or vapor at the surface.
• Evapotranspiration is the sum of evaporation from the land surface and transpiration from plants.
• Factors that affect evaporation:
  • Temperature: Higher temperature increases evaporation rate.
  • Humidity: Lower humidity increases evaporation rate.
  • Wind speed: Higher wind speed increases evaporation rate.
  • Surface area: Increased surface area increases evaporation rate.
• Evaporation pan: A device used to measure the rate of evaporation from open water surfaces.

Potential Evapotranspiration (PET)

• PET is the amount of water that would be evapotranspirated if there were no water limitations.
• Thornthwaite method: A method used to estimate PET based on temperature, humidity, and wind speed.
• PET is higher in humid climates and lower in arid climates.

Evapotranspiration and Hydrological Cycle

• Evapotranspiration is an important component of the hydrological cycle, returning water vapor to the atmosphere.
• ET contributes to groundwater recharge, affects precipitation levels, and influences river flow.

Evaporation and Temperature

• Evaporation cools the liquid remaining, as high-energy molecules leave the liquid.
• Increased temperature generally speeds up the rate of evaporation.

Measurement of Evapotranspiration

• ET is harder to quantify using instrumental measurements, but it is easier to predict than rainfall.
• Quantification includes evaporation from soil, groundwater, and plants, and transpiration from plants.

Factors Affecting Evapotranspiration

• Vegetation type and density affect ET rates, with dense vegetation generally increasing ET.
• Shading decreases ET, as it reduces the amount of solar radiation available for evaporation.
• Soil moisture affects ET, as plants will not transpire if the soil is too dry.

Groundwater

• Permeability: The ability of a rock or soil to allow water to flow through it.
• Porosity: The amount of empty space in a rock or soil that can hold water.
• Grain size, sorting, and cementation affect permeability and porosity.
• Aquifers: Underground layers of permeable rock or soil that store and transmit large amounts of water.

Unit Hydrograph

• A hydrograph that shows the response of a watershed to a unit of rainfall.
• Used to predict runoff from a watershed based on rainfall data.

Water Table and Zone of Saturation

• Water table: The upper surface of the zone of saturation in groundwater.
• Zone of saturation: The area below the water table where the soil is fully saturated with water.
• Capillary fringe: The area above the water table where the soil is partially saturated with water.

Evaporation and Evapotranspiration

• Evaporation is the process where a liquid transforms into a gas or vapor at the surface.
• Evapotranspiration is the sum of evaporation from the land surface and transpiration from plants.
• Factors that affect evaporation:
  • Temperature: Higher temperature increases evaporation rate.
  • Humidity: Lower humidity increases evaporation rate.
  • Wind speed: Higher wind speed increases evaporation rate.
  • Surface area: Increased surface area increases evaporation rate.
• Evaporation pan: A device used to measure the rate of evaporation from open water surfaces.

Potential Evapotranspiration (PET)

• PET is the amount of water that would be evapotranspirated if there were no water limitations.
• Thornthwaite method: A method used to estimate PET based on temperature, humidity, and wind speed.
• PET is higher in humid climates and lower in arid climates.

Evapotranspiration and Hydrological Cycle

• Evapotranspiration is an important component of the hydrological cycle, returning water vapor to the atmosphere.
• ET contributes to groundwater recharge, affects precipitation levels, and influences river flow.

Evaporation and Temperature

• Evaporation cools the liquid remaining, as high-energy molecules leave the liquid.
• Increased temperature generally speeds up the rate of evaporation.

Measurement of Evapotranspiration

• ET is harder to quantify using instrumental measurements, but it is easier to predict than rainfall.
• Quantification includes evaporation from soil, groundwater, and plants, and transpiration from plants.

Factors Affecting Evapotranspiration

• Vegetation type and density affect ET rates, with dense vegetation generally increasing ET.
• Shading decreases ET, as it reduces the amount of solar radiation available for evaporation.
• Soil moisture affects ET, as plants will not transpire if the soil is too dry.

Groundwater

• Permeability: The ability of a rock or soil to allow water to flow through it.
• Porosity: The amount of empty space in a rock or soil that can hold water.
• Grain size, sorting, and cementation affect permeability and porosity.
• Aquifers: Underground layers of permeable rock or soil that store and transmit large amounts of water.

Unit Hydrograph

• A hydrograph that shows the response of a watershed to a unit of rainfall.
• Used to predict runoff from a watershed based on rainfall data.

Water Table and Zone of Saturation

• Water table: The upper surface of the zone of saturation in groundwater.
• Zone of saturation: The area below the water table where the soil is fully saturated with water.
• Capillary fringe: The area above the water table where the soil is partially saturated with water.