Evaporation and Pan Coefficient

Evaporation refers to the process of transformation of liquid water into water vapor. The rate of evaporation is determined by various factors such as temperature, humidity, wind speed, solar radiation, and surface area of water. The process of evaporation is important in many fields such as agriculture, hydrology, meteorology, and water resources management.

Pan coefficient is a term used in evaporation studies to denote the ratio of actual evaporation from a water surface to the theoretical evaporation from a standard pan. The standard pan is a shallow, cylindrical container with a diameter of 121.9 cm and a depth of 25.4 cm. The pan coefficient is affected by various factors such as wind speed, humidity, and surface characteristics of the pan.

USWB Class A Pan Evaporimeter

The USWB (United States Weather Bureau) Class A Pan Evaporimeter is a standard instrument used for measuring evaporation. It is a cylindrical pan with a diameter of 121.9 cm and a depth of 25.4 cm. The pan is painted white to minimize solar absorption, and it is filled with water up to a depth of 10 cm. The instrument is placed on a level, natural ground surface with a minimum of obstruction from nearby trees or buildings.

The pan coefficient of the USWB Class A Pan Evaporimeter is determined by comparing the actual evaporation from the pan to the theoretical evaporation from a standard pan. The pan coefficient is affected by various factors such as wind speed, humidity, and surface characteristics of the pan. The average pan coefficient of the USWB Class A Pan Evaporimeter used for evaporation is 0.70.

Answer

The correct answer is option 'B', which is 0.70. The average pan coefficient of the USWB Class A Pan Evaporimeter used for evaporation is 0.70. This means that the actual evaporation from the pan is 70% of the theoretical evaporation from a standard pan. The pan coefficient is affected by various factors such as wind speed, humidity, and surface characteristics of the pan.