It is obvious that air transports water vapour from one area to another, despite the transport, humidity has local variation. Give clear description on the determinants of the variation.

Humidity is the amount of water vapour in air. No air which is absolutely dry but the amount of water vapour in the atmosphere tends to differ from one place to another, Example in Equatorial regions their air contains much water compared to tropical desert areas. Humidity is measured by an instrument known as hygrometer. The source of air to contain water vapour includes sun’s heat, convergence of air masses of different temperature and orographic air rise. Humidity can be measured in various ways including specific humidity, relative humidity, mixing ratio and absolute humidity. Local variation of humidity occurs due to the following factors:-

Water bodies, water bodies facilitates the occurrence of evaporation, by which moisture is carried into the atmosphere due sun’s heat causing air to rise in convectional current and cause the area to become humid. Evaporation makes the atmosphere become saturated with water vapour and possibly reaches a dew point. Areas with many water bodies like rivers and oceans are more humid compared to areas with no or few water bodies like desert areas. Example coastal areas are more humid because they are around water body system which influences evaporation which results to the release of water vapour into atmosphere unlike areas which are for from water body system.

Vegetation; Vegetation influenced the process of transpiration and evapotranspiration of water through stomata into atmosphere. Areas covered by vegetation are more humid than areas with no vegetation cover. Transpiration is a biological process by which water is lost from a plant through the minute pores or stomata. In its leaves into atmosphere and make the atmosphere becomes more humid. Evapotranspiration is the loss of water from the soil through roots to different parts of plants and then into atmosphere to make an air humid. Therefore areas with vegetation cover are more humid than those with no vegetation cover. Also vegetation influences the formation of rainfall which also plays a big role in making an area become humid.

Amount of solar radiant energy reaches on the earth’s surface. Areas with high amount of solar radiant energy reaches on the earth’s surface are more humid than areas with low amount of solar radiant energy reaches on the earth surface. High insolation causes water to evaporate from the land and water bodies into atmosphere to release water vapour air rise in convectional currents. This results to the increase of water vapour into the atmosphere. In areas with less heat air cools and become stable to rise upward. Example, Equatorial areas are more humid because they receive more solar radiant energy which warm the surface and made moist air to rise upward in great convectional currents to cause saturation unlike in Polar Regions where temperature is low.

Prevailing wind, this is the one that blows frequently from one direction than from any other direction. Also on shore and offshore winds have greater influence in the variation of humidity in different areas. Example in coastal areas on shore winds cause an air becomes saturated with moisture from the sea and this increase the level of humidity while offshore winds cause the area to become less saturated because moisture is carried away from the land to the sea, hence reduce the level of humidity.

Relief; Windward side of the mountain are more humid than leeward side of the mountain. Windward side of the mountain faces more directly the moist air but leeward side of the mountain faces away the moist air. In windward side air which is moist air is forced to rise vertically by a mountain and this geographical perspective is referred to as orographic air rise. This phenomenon is a source for an air to have humidity, but the leeward side is less humid as it faces away the moist.

Altitude, areas with high altitude have low degree of dampness as moist warm air do not reaches to make saturation. Also they lack particles which absorb moisture, hence they have low humidity. Low altitude areas are closer to water bodies, hence through evaporation they are humid than high altitude areas. Water bodies like oceans and rivers play a great role in making a place become more humid because they contain a lot of impurities which absorb moisture.

By conclusion, it is obvious that air transports water vapour from one area to another, despite the transport humidity has local variation. The variation is caused by water bodies, vegetation, amount of solar radiant energy reaches on the earth’s surface, altitude, ocean currents, prevailing wind and relief.

REFERENCES

Critchfield, H. J. (1974), General Climatology, 3rdEdition, Prentice Hall, Inc. ,Egglewood Cliffs, New Jersey.

Henderson-Sellers, A. & Robinson, P., 1986, Contemporary Climatology. Longman.