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Here is a compilation of essays on ‘Humidity’ for Class 6, 7, 8, 9 and 10. Find paragraphs, long and short essays on ‘Humidity’ especially written for school students.
Essay on Humidity
Essay Contents:
- Essay on the Meaning of Humidity
- Essay on the Formation of Humidity
- Essay on the Measurement of Humidity
- Essay on the Influence of Humidity on Crops
- Essay on Humid Cities on Earth
Essay # 1. Meaning of Humidity:
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Humidity of the air refers to the content of water vapour present in the air at a particular time and place. On the other hand, water vapour is the gaseous form of water. Water vapour represents 2 per cent of the total composition of the atmosphere but this percentage varies both spatially and temporally as it ranges from zero to 5 per cent.
Nearly 50 per cent of the total atmospheric vapour is concentrated in the lower atmosphere upto the height of 2000 metres. It may be mentioned that water occurs in three states viz. as solid (e.g., ice, snow and frost), as liquid (e.g., water), and in gaseous form (e.g., vapour). The presence of water vapour in the atmosphere is a vital factor for weather conditions of a particular region.
The nature and amount of precipitation, the amount of loss of heat through radiation from the earth’s surface, surface temperature, latent heat of the atmosphere, stability and instability of air masses etc. depend on the amount of water vapour present in the atmosphere. The atmospheric water vapour is derived through evaporation of water from oceans and seas, terrestrial lakes, land water bodies (tanks, ponds), rivers etc.
The process of transformation of liquid (water) into gaseous form is called evaporation. The amount and intensity of evaporation depend on aridity, temperature and velocity of winds. The higher the aridity, temperature and velocity of winds, the higher the rate and amount of evaporation because dry air with high temperature is capable of retaining more moisture (vapour) as dry air requires more time and moisture to become saturated.
A stable air becomes saturated soon because there is no transfer of moisture while unstable air attains saturation quite late because there is much transfer of moisture. There is more evaporation from the oceans than from the lands. There is maximum evaporation from the lands between 10°N and 10°S latitudes whereas maximum evaporation occurs from the oceans between 10°-20° latitudes in both the hemispheres.
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The process of conversion of vapour into liquid (water) and solid form (ice, snow, frost) is called condensation. It is apparent that evaporation and condensation are opposite processes wherein the former involves conversion of liquid (water) into gaseous form (water vapour) while the latter refers to conversion of water vapour into liquid or solid form.
Essay # 2. Formation of Humidity:
Energy in the form of heat is required for the conversion of water into gaseous form (water vapour). Heat energy is generally measured in the unit of calorie, 79 calories are required to convert one gram of ice into water whereas 607 calories are needed for the conversion of one gram of water into water vapour.
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It is apparent that the potential energy of water is more than ice and that of vapour is more than water. This hidden amount of heat in water vapour is called latent heat. In other words, the amount of heat spent during the process of evaporation is never lost rather it is always associated with water vapour. There are several evidences which demonstrate the use of heat energy at the time of evaporation.
For example:
(i) one feels cooling effect when one sits before fan or in shady open air after sweating in summer months because the sweats are evaporated,
(ii) there is cooling effect when drops of sprit are kept on the palm of human hand because sprit is evaporated etc.
On the other hand, heat energy is released at the time of condensation (conversion of vapour into liquid or solid form). This energy, released after condensation, is called latent heat of condensation.
Essay # 3. Measurement of Humidity:
Humidity refers to the content of water vapour present in the air in gaseous form at a particular time and place. The atmospheric humidity is obtained through various processes of evaporation from the land and water surfaces of the earth.
The atmospheric humidity is of vital climatic significance because different forms of precipitation (dew, fog, rainfall, frost, snowfall, hailstorm etc.), atmospheric storms (cyclones) and turbulence etc. depend on humidity. The atmospheric humidity is expressed in a number of ways e.g., absolute humidity, specific humidity, relative humidity etc.
i. Humidity Capacity:
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The moisture content (humidity) of the air is measured in grain per cubic foot or in gram per cubic centimetre. Evaporation is the main mechanism through which water is converted into humidity (vapour). Since temperature and evaporation are directly positively related (evaporation increases with increasing temperature) and hence humidity and temperature are also directly positively related.
The moisture retaining capacity or humidity capacity refers to the capacity of an air of certain volume at certain temperature to retain maximum amount of moisture content. Humidity capacity is directly positively related with temperature i.e., higher the temperature, higher the humidity capacity and lower the temperature, lesser the humidity capacity. In other words, as air temperature increases, humidity also increases and vice-versa.
For example, the humidity capacity of an air having the volume of one cubic foot and temperature of 30°F is 1.9 grain whereas it becomes 2.9 grain when temperature becomes 40°F (an increase of 10°F). It may be pointed out that the ratio of increase of humidity capacity also increases with increasing temperature (Table 36.1).
For example, the net increase of humidity capacity from 30°F to 40°F is one grain while it becomes 5 grain from 90°F to 100°F (table 36.1). Similarly, humidity capacity becomes higher during summer months than during winter months and during daytime than nights.
The extent of land and water and wind velocity also influence humidity capacity. Oceanic and coastal areas record higher humidity capacity of air than the remote areas of the continents. Humidity capacity decreases from equator pole-ward. The air having moisture content equal to its humidity capacity is called saturated air.
ii. Absolute Humidity:
The total weight of moisture content (water vapour) per volume of air at definite temperature is called absolute humidity. Generally, absolute humidity does not change with increase or decrease of temperature, if no additional vapour is added through additional evaporation, but it changes with contraction (after descent) or expansion (on ascent) of air.
The absolute humidity decreases from equator towards the poles and from oceans to the continents. The possibility of precipitation largely depends on absolute humidity.
iii. Specific Humidity:
Specific humidity is defined as the mass of water vapour in grams contained in a kilogram of air and it represents the actual quantity of moisture present in a definite air. Specific humidity is seldom affected by changes in air pressure or air temperature because it is measured in the units of weight (grams).
It is directly proportional to vapour pressure, which is ‘the partial pressure exerted by water vapour in the air and is independent of other gases’, and is inversely proportional to air pressure. Specific humidity decreases from equator pole-ward.
For example, extremely cold and dry air over arctic region during winter generally has specific humidity of 0.2 gram per kilogram of air while it becomes as high as 18 grams per kilogram of extremely warm and moist air over equatorial regions. ‘In a real sense, specific humidity is a geographer’s yardstick of a basic natural resource- water-to is applied from equatorial to Polar Regions. It is a measure of the quantity of water that can be extracted from the atmosphere as precipitation’.
iv. Relative Humidity:
Relative humidity is defined as a ratio of the amount of water vapour actually present in the air having definite volume and temperature (i.e., absolute humidity) to the maximum amount the air can hold (i.e., humidity capacity). In other words, relative humidity is the proportion of absolute humidity of an air of definite volume at a given temperature to the humidity capacity of that air. Relative humidity is generally expressed as percentage.
For example, if the humidity capacity and absolute humidity of an air having temperature of 20°C are 8 grains and 4 grains per cubic foot respectively, then the relative humidity will be as follows:
Relative humidity = Absolute humidity/Humidity capacity × 100
4/8 x 100 = 50% or 1/2 or 1:2
There is inverse relationship between air temperature and relative humidity i.e., relative humidity decreases with increasing temperature while it increases with decreasing temperature (table 36.2).
When the humidity capacity and absolute humidity of the air are the same, the air is said to be saturated and the relative humidity becomes 100 per cent.
Essay # 4. Influence of Humidity on Crops:
Relative humidity directly influences water relations of plant and indirectly affects leaf growth, photosynthesis, pollination, occurrence of diseases and finally economic yield. Dryness of atmosphere, as represented by saturation deficit (100-RH), reduces dry matter production through stomatal control and leaf water potential.
Leaf Growth:
Leaf growth not only depends on synthetic activities resulting from biochemical process but also upon physical process of cell enlargement. Cell enlargement occurs as a result of turgor pressure developed within the cells. Turgor pressure is high under RH due to less transpiration. Thus, leaf enlargement is high in humid areas.
Photosynthesis:
Photosynthesis is indirectly affected by RH. When RH is low, transpiration increases causing water deficits in plant. Water deficits cause partial or full closure of stomata and increase mesophyll resistance, blocking entry of carbon dioxide.
Pollination:
Moderately low air humidity is favourable for seed set in many crops, provided soil moisture supply is adequate.
For example, seed set in wheat was high at 60 per cent RH compared to 80 percent when water availability in the soil was not limiting. At high RH, pollen may not be dispersed from the anthers.
Pests:
Incidence of insect pests and diseases is high under high humidity conditions. High RH favours easy germination of fungal spores on plant leaves. Blight diseases of potato and tea spread more rapidly under humid conditions. Several insects such as aphids and jassids thrive better under moist conditions.
Grain yield:
Very high or very low RH is not conducive for high grain yield. Under high humidity, RH is negatively correlated with grain yield of maize and wheat. It can be attributed to adverse effect of RH on pollination and high incidence of pests.
On the contrary, increase in RH during panicle initiation to maturity increased grain yield of sorghum under low humidity conditions due to favourable influence of RH on water relations of plants and photosynthesis.
With similar amount of solar radiation, crops that are grown with irrigation gives less yield compared to those grown with equal amount of water as rainfall. This is because the dry atmosphere, which is little affected by irrigation, independently suppresses the growth of crops.
Very high relative humidity leads to:
i. Reduced evapotranspiration.
ii. Increased heat load of plants.
iii. Stomatal closure.
iv. Reduced CO2 uptake.
v. Reduced transpiration influences translocation of food materials and nutrients.
vi. Moderately high RH of 60-70% is beneficial.
vii. Low RH increases the evapotranspiration.
Essay # 5. Humid Cities on Earth:
Most humid cities on earth are, generally, located closer to equator, near coastal regions. Cities in south and Southeast Asia are among the most humid, such as Kolkata and those in Kerala in India, cities of Manila in the Philippines and Bangkok in Thailand: these places experience extreme humidity during their rainy seasons combined with warmth giving the feel of a lukewarm sauna.
Darwin, Australia experiences an extremely humid wet season from December to April. Shanghai (China) and Hong Kong also have an extreme humid period in their summer months. Kuala Lumpur and Singapore have very high humidity all year round because of their proximity to water bodies and the equator and overcast weather; despite sunshine, perfectly clear days are rare in these locations and it is often misty.
In cooler places such as Northern Tasmania, Australia etc. high humidity is experienced all year due to ocean between mainland Australia and Tasmania. In summer, hot dry air is absorbed by this ocean and temperature rarely climbs above 35°C.
In USA, most humid cities, strictly in terms of relative humidity are Forks and Olympia and Washington. This fact may come as a surprise to many, as the climate in this region rarely exhibits discomfort usually associated with high humidity. Dew points are typically much lower on West Coast than on East.
Because high dew points play a more significant role than relative humidity in discomfort created during humid days, air in these western cities usually does not feel “humid.” Highest dew points are found in coastal Florida and Texas.
The US city with lowest annual humidity is Yuma, Arizona, averaging under 50 per cent for a high and 22 per cent as a low. Next lowest humidity is Tucson, Arizona, with average high humidity of 57 per cent and a low of 26 per cent. Lowest in the world is Antarctica.