Factors Affecting Climate Part – 1

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In the preceding lessons, we have discussed about the temperature, atmospheric pressure, winds and precipitation. These elements of weather have an important effect on our lives including the houses we construct, the clothes we wear, and the food we prefer. All of these mainly depend on weather and climatic conditions. We will now study about the difference among weather, season and climate and also the factors affecting climate of a place.

Objectives

The major objectives of this chapter are:

  • To name the various elements of weather and climate

  • To differentiate among weather, season, and climate

  • To explain the need for forecasting weather in advance

  • To explain with specific examples the various factors affecting the climate of a place or region

  • To describe the important characteristics of each thermal zone

  • To state Koeppen’s classification of climate

Weather and Climate

Weather: Temperature, pressure, wind, humidity, and precipitation, interact with each other and influence the atmospheric conditions including the direction and velocity of wind, amount of insolation, cloud cover, and the amount of precipitation. The influence of these elements differs from place to place and time to time. It may be restricted to a small area and for a short duration of time. We very often describe this influence in the name of weather as sunny, hot, warm, cold, fine, etc. depending upon the dominant element of weather at a place at a point of time. Therefore, weather is the atmospheric condition of a place for a short duration with respect to its one or more elements. Two places even a short distance apart may have different kind of weather at the same time.

Weather Forecast: It is important to know the coming weather in advance. Farmers, sailors, aviators, tourists and many others are interested to know the weather conditions in advance for their own benefits. Newspapers publish weather reports and weather forecasts along with a map showing this information. Better weather forecasts are available with the use of weather satellites. When a cyclone or dangerous weather is expected, warnings are issued over the radio, television and newspapers so that people can prepare to save themselves and their property from the hazard.

The weather office collects data on temperature, wind, cloud cover, rainfall, and other atmospheric phenomena through its numerous observation centres. These centres are scattered all over the country. Similar information is also received from the ships sailing in the high seas. The analysis of these data thus collected, helps in forecasting weather conditions for the next 48 hours or even for a week. The significance of a weather information supplied through a map and its forecast is better utilised in a country like the U.K. where weather changes are very rapid.

Season: A year is divided into seasons depending upon variations in atmospheric conditions. They are specified periods in a year which have similar weather conditions. Season is a period of the year characterized by a particular set of weather conditions resulting from the inclination of the earth’s axis and the revolution of the earth round the sun. The same cycle of season is repeated year after year. Four seasons, each of three months duration have been recognized in temperate regions. They are spring, summer, autumn, and winter. In our country, the Indian Meteorological Department has recognized four main seasons. They are:

  1. Cold Weather Season from December to February

  2. Hot Weather Seasons from March to May

  3. Advancing Monsoon Season or Rainy Season from June to September

  4. Retreating Monsoon Season from October to November

Traditionally, there are six seasons in north India. They are:

  1. Basant Ritu (Chaitra- Vaisakh or March-April)

  2. Greeshm Ritu (JaysthaAsharh or May-June)

  3. Varsha Ritu (Shravan-Bhadrapad or July-August)

  4. Sharad Ritu (Aswina-Kartika or September- October)

  5. Hemant Ritu (Margashirsh-Posh or November-December)

  6. Shishir Ritu (Magh Falgun or January-February)

The rays of the sun are more or less direct on the equator throughout the year. Hence, equatorial regions experience the same temperature all the year round. Therefore, seasons are insignificant on or near the equator. Near the coast, the oceanic influence reduces the seasonal variations. In the Polar Regions, there are only two seasons i.e., long winter and short summer.

Climate: The average weather conditions, prevalent from one season to another in the course of a year, over a large area are known as climate. The average of these weather conditions is calculated from the data collected for several years or about 35 years for a larger area. For example, Rajasthan experiences hot and arid climate, Kerala has tropical rainy climate, Greenland has cold desert climate, and the climate of central Asia is temperate continental. Climate of a region is considered more or less permanent.

The Difference between Weather and Climate Can be Seen As:

  • Weather is the study of atmospheric conditions for short duration of a limited area. Climate is the study of the average weather conditions observed over a long period of time for a larger area.

  • Weather is influenced by anyone of its predominant elements i.e., temperature or humidity. Climate is the collective effect of all its elements.

  • The weather changes very often. Climate is more or less permanent.

  • Weather is experienced over small areas of a country. Climate is experienced over large area of the continent.

  • A place can experience different types of weather conditions in a year. But a place can experience only one type of climate.

Factors Affecting Climate

Different regions of the world have differences in temperature, humidity, and precipitation. These differences influence the lifestyle of the people living under different climatic conditions. To understand different climatic conditions, let us discuss the factors which cause the variations in the climate of a place or a region.

Latitude or Distance from the Equator: The places near the equator are warmer than the places which are far away from it. This is because the rays of the sun fall vertical on the equator and slanting in the temperate and polar regions. The vertical rays are concentrated over a small area than the slanting one. The vertical rays pass through a shorter distance in the atmosphere before reaching the earth’s surface. Therefore, lower the latitude higher is the temperature and vice versa. For example, Malaysia which is near the equator is warmer than England which is far away from the equator.

Altitude or the Height from the mean sea level: We all know that mountains are cooler than the plains. Shimla situated on a higher altitude is cooler than Jalandhar, although both are almost on the same latitude. The temperature decreases with the height of a place. For a vertical rise of 165 metres there is an average decrease in temperature at the rate of 1°C. Thus, the temperature decreases with increase in height.

Distance from the Sea: The water is a bad conductor of heat i.e., it takes longer time to heat and longer time to cool. Due to this moderating effect of the sea, places near the coast have low range of temperature and high humidity. The places in the interior of the continent do not experience moderating effect of the sea. These places have extreme temperatures. The places far from the sea have higher range of diurnal and annual temperatures. Mumbai has relatively lower temperature and higher rainfall than Nagpur, although both are almost situated on the same latitude.

Nature of the Prevailing Winds: The onshore winds bring the moisture from the sea and cause rainfall on the area through which they pass. The offshore winds coming from the land are dry and help in evaporation. In India, the onshore summer monsoon winds bring rains while offshore winter monsoon winds are generally dry.

Cloud Cover: In areas generally having cloudless sky as in deserts, temperature even under shade are very high because of the hot daytime sunshine. At night this heat radiates back from the ground very rapidly. It results in a large diurnal range in temperature. On the other hand, under cloudy sky and heavy rainfall at Thiruvananthapuram the range of temperature is very small.

Ocean Currents: Ocean waters move from one place to another partly as an attempt to equalize the temperature and density of water. Ocean currents are large movements of water usually from a place of warm temperature to one of cooler temperature or vice-versa. The warm ocean currents raise the temperature of the coast and sometimes bring rainfall. On the other hand, the cold currents lower the temperature and create fog near the coast. Port Bergen in Norway is free from ice even in winter due to warm North Atlantic Drift while Port Quebec in Canada remains frozen during winter months due to chilling effect of the Cold Labrador Current in spite of the fact that Port Quebec is situated in much lower latitude than Port Bergen. The onshore winds passing over a warm current carry warm air to the interior and raise the temperature of the inland areas. Similarly, the winds blowing over cold current carry cold air to the interior and create fog and mist.

Direction of Mountain Chains: The mountain chains act as natural barrier for the wind. The onshore moisture laden winds are forced to rise after striking against the mountain, and give heavy rainfall on the windward side. These winds descending on the leeward side cause very low rainfall. The great Himalayas check the moisture laden monsoon winds from crossing over to Tibet. This mountain chain also checks biting polar cold winds from entering into India. This is the reason for which northern plains of India get rains while Tibet remains a perpetual rain shadow area with lesser amount of rainfall.

Slope and the Aspect: The concentration of heat being more on the gentler slope raises the temperature of the air above them. Its lesser concentration along steeper slopes lowers the temperature. At the same time, mountain slopes facing the sun are warmer than the slopes which are away from the sun’s rays. The southern slopes of Himalayas are warmer than the northern slopes.

The Nature of the Soil and Vegetation Cover: The nature of soil depends upon its texture, structure and composition. These, qualities vary from soil to soil. Stony or sandy soils are good conductor of heat while black clay soils absorb the heat of the sun’s rays very quickly. The bare surface reradiates the heat easily. The deserts are hot in the day and cold in the night. The forest areas have lower range of temperature throughout the year in contrast to non-forested areas.

Schematic Representation of Possible Influences

Schematic Representation of Possible Influences

Schematic Representation of Possible Influences

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