Weather is defined as the condition of the atmosphere of a place at a certain time over a short period. The weather of a place is always very brief and changes regularly e.g. the weather of today could be sunny, rainy or cloudy, etc.
Climate is defined as the average atmospheric conditions of an area over a long period of time. Unlike weather, climate of a place lasts for a very long time before it can change.
ELEMENTS OF WEATHER AND CLIMATE
The elements of weather and climate include:
- Relative humidity.
- Cloud cover.
- Temperature: Heat within the air indicates how hot or cold a place is and varies from latitude to latitude. The sun is the source of all heat, measured with the aid of Thermometer. It influences the actual amount of water vapour present in the air and also the rate of evaporation and condensation. In the lower atmosphere, temperature decreases with heights.
- Pressure: This consists of a number of mixed gases and has weight which it exerts on earth surface. It varies from place to place and from time to time. The higher one goes, the lower the temperature and pressure. Pressure is measured with a Barometer.
- Cloud: These particles of water droplets in the upper atmosphere suspended in the air. Due to condensation of water vapour carried by rising air, clouds may give precipitation. Cloud reduces visibility and depletes solar insulation. Types of cloud include cirrus, cumulus and stratus.
- Sunshine: This is the visible part of the solar energy. It is useful for plants and other living organisms. It determines how dry the wind is and aids the process of formation of clouds and rainfall. The amount of sunshine depends on the latitude of a place and the slope of the land. Sunshine varies according to season.
- Rainfall: Rainfall refers to water droplets from the atmosphere. It occurs as a result of evaporation from water bodies e.g. rivers, lakes, ocean and transpiration from plants. Condensation reaches saturation point, dew point is finally reached. The amount of rainfall is measured with the aid of a Rain gauge. The different types of rainfall are convectional, orographic and cyclonic.
- Wind: This is air in motion, from high pressure to low pressure belts. It has special mode of direction and is made up of series of dusts and eddies, capable of carrying moisture, dust and other pollutants. Wind adapts to the characteristics of its immediate environment. The direction is measured with Wind vane while the speed is measured with Anemometer.
- Humidity: This is a measure of the dampness of the atmosphere due to water in the gaseous state and it varies from place to place at different times of the day. Two types exist: absolute and relative humidity and it is measured with Hygrometer.
FACTORS AFFECTING WEATHER AND CLIMATE
Climate varies from one part of the world to another due to the effects of the following factors:
- Latitude: Latitude refers to the location of a place on the earth’s surface in relation to the equator. Tropical latitudes, where the sun’s altitude is always high have hotter temperature than lower latitudes where the sun’s altitude is generally low. These differences in temperature in relation to different latitudes affect climate.
- Altitude: Altitude refers to the height of a place above the sea-level. As one moves higher into the atmosphere, the temperature decreases by 6.5˚C for every 1000m of ascent. This is called the normal lapse rate. High altitudes like high mountains contain less dust and water vapour and so allow heat to escape easily and remain cold.
- Continentality or distance from the sea: Generally, the further the inland is from the sea, the less the rainfall e.g. Freetown on the coast and Timbuktu on the inland. Lower temperature range exists along the coast than inland e.g. Calabar (less than 30˚C) and Agades (more than 15˚C). Higher humidity also occurs along the coast than further inland generally. There is also thicker cloud cover along the coast than inland.
- Ocean currents: Ocean currents can affect the climate of adjacent coast land. For instance, cold currents lower the temperature of adjacent coast lands e.g. Benguella current. Cold current help in the formation of fogs along the coast e.g. Cold Benguella and Canaries currents. Warm currents raise temperature of the adjacent coast lands e.g. warm Guinea and Warm Mozambiquan current. Cold currents result in the formation of coastal deserts e.g. Kalahari Desert, because of cold Benguella current, Sahara desert because of cold canaries current.
- Planetary winds and pressure belts: Winds can affect the climate of adjacent coastland. For example, warm winds raise the temperature of adjacent coastlands e.g. the westerlies bring warm air into Western Europe. Cold winds lower the temperature of adjacent coast lands e.g. cold polar winds lower the temperature of the coasts of Newfoundland. Warm, moist winds from the ocean bring rainfall to the adjacent coastlands e.g. S.W. Monsoon in West Africa. Dry winds from the interior do not produce rain, rather they produce dust and dryness e.g. North-East trade wind brings no rain but dust and dryness to the coastal lands of West Africa. Off shore winds blowing from the interior to the coast produce fogs at the coast e.g. fog formation along the Namibian coast.
- Slope and aspect: Steep slope experienced more rapid change in temperature than a gentle slope.
- Cloud cover: Cloud reduces the amount of solar radiation reaching the earth’s surface and the amount of solar radiation escaping from the earth surface into space. Day temperature in the equatorial region is always high because of the heavy cloud cover.
- Natural vegetation and soil: The thick foliage (leaves) of heavy forest cuts off much of the incoming sunlight energy (insolation). As a result, the forest temperature is cool and lower than that of the open ground (soil). Light soils reflect more heat than darker soils which are better absorbers of heat.
IMPORTANCE OF WEATHER AND CLIMATE TO MAN
- Human settlement: Weather and climate affect the rate at which human beings live in a place. Temperate areas are more habitable than desert areas because of differences in climate.
- Health: Humid or damp environment encourage the growth of micro-organisms which cause the diseases of man; hence, death rate is higher in tropical than in temperate countries.
- Environmental hazards: Hazards like soil erosion, rain storm, flood and drought are caused by difference in weather and climate of a place.
- Vegetation: Temperature and rainfall are the major determinants of the type of vegetation in an area which could be light or thick.
- Clothing: The types and nature of clothing worn by different people in different parts of the world is due to differences in climate. Cold climate requires black and thick dresses while hot climate requires light dresses.
- Housing: The type and nature of houses built in different places is also influenced by differences in climate e.g. Hot regions require air-conditioned houses; whereas, Polar Regions do not.
- Agriculture: Rainfall and temperature are important elements that determine the type of crops to be cultivated in an area.
- Soil formation: Soil is formed from parent rocks which have been broken by elements of weather and climate. The rate of disintegration of rocks to form soil is principally a factor of climate.
- Communication and transportation: The type of transportation used in an area is greatly influenced by weather and climate. Air-conditioned vehicles are popular in tropical climates while such vehicles are not popular in Polar Regions. Fog disrupts flight in temperate regions while harmattan does the same in the tropics and both cause poor visibility.
- Occupation: The climate of a place do determine the occupation of the people in that particular region e.g. people living in equatorial type of climate are more likely to be involved in cash crop farming and lumbering of hardwood.
- Cultural activities: The climate of a place can also affect the cultural activities of some people e.g. winter or summer sports.
- Health: The health status of a particular area can be determined by the type of climate. The sub-tropical climate is said to favour the breeding of mosquitoes which causes malaria fever.