Geography: Module 4 - The Natural Environment - Weather, Climate & Vegetation

Weather

Day-to-day variation of atmospheric and climatic conditions at any one place over a short period of time. Such conditions include humidity, precipitation, temperature, cloud cover, visibility and wind, together with extreme phenomena such a storms and blizzards. It differs from climate in that the latter is a composite of the average weather conditions of a locality or region over a long period of time (at least 30 years).

Rainfall

A form of precipitation in which drops of water fall to the Earth’s surface from clouds. The drops are formed by the accumulation of fine droplets that condense from water vapour in the air. The condensation is usually brought about by rising and subsequent cooling of air.

Humidity

The quantity of water vapour in a given volume of air (absolute), or the ratio of the amount of water vapour in the atmosphere to the maximum amount the air can hold (relative). At dew point the relative is 100% and the air is said to be saturated. Condensation (the conversion of vapour to liquid) may then occur.

Air Pressure

The pressure at any point on the Earth’s surface that is due to the weight of the air above it; it decreases as altitude increases. At sea level, the average is 101.3 millibars (mb). Areas of relatively high pressure are called anticyclones; areas of low pressure are called depressions.

Rain Gauge

An instrument used to measure precipitation, usually rain. It consists of an open-topped cylinder, inside which there is a close-fitting funnel that directs the rain to a collecting bottle inside a second, inner cylinder.

Stevenson Screen

A box designed to house weather-measuring instruments such as thermometers. It is kept off the ground by legs, has louvred sides to encourage the free passage of air, and is painted white to reflect heat radiation.

Maximum-Minimum Thermometer

A thermometer that shows both the maximum temperature in a given time period and the minimum temperature in the same time period.

Cloud

Water vapour condensed into millions of miniature water particles that float in the atmosphere. They are formed by the cooling of air containing water vapour, which generally condenses around tiny dust or ice particles.

Natural Vegetation:

The type of vegetation that would be found in an area if there was no human impact. For example, this type of vegetation of the British Isles is oak woodland, as that is the species best able to tolerate the temperate climate of that part of the world.

Climate

The combination of weather conditions at a particular place over a period of time - usually a minimum of 30 years. It includes the averages, extremes and frequencies of all meteorological elements such as temperature, atmospheric pressure, precipitation, wind, humidity and sunshine.

Tropical Rainforest

Dense forest usually found on or near the equator where the climate is hot and wet. The vegetation typically includes a canopy formed by high branches of tall trees providing shade for lower layer an intermediate layer of shorter trees and tree roots, lianas, and a ground cover of mosses and ferns.

Convectional Rainfall:

Rainfall associated with hot climates, resulting from the rising of convection currents of warm air. Air that has been warmed by the extreme heating of the ground surface rises to great heights and is cooled quickly. The water vapour carried by the air condenses and rain falls heavily. It is usually associated with a thunderstorm.

Altitude:

Measurement of height usually given in metres above sea level. Temperature declines, on average 1^oC for every 100m (and therefore rises 1^oC with every decrease of 100m).

Prevailing Wind:

The direction from which the wind most commonly blows in a region. In the British Isles, for example, it is south-westerly, blowing from the Atlantic Ocean and bringing moist and mild conditions.

Biodiversity:

A measure of the variety of the Earth’s plant and animal species, of genetic differences within species, and of the ecosystem that support those species.

Soil

The outermost layer of the Earth’s solid surface consisting of weathered rock, air, water and decaying organic matter overlying the bedrock. It comprises minerals, organic matter (humus) derived from decomposed plants and organisms, living organisms, air and water.

Ecosystem:

An integrated unit consisting of a community of living organisms (animals and plants) and the physical environment (air, soil, water and climate) that they inhabit. Individual organisms interact with each other and with their habitat.

Desert:

A dry area with limited vegetation. They can be either hot or cold. Common characteristics include irregular rainfall of less than 250mm per year.

Drought

An extended period of dry weather leading to conditions of extreme dryness. Absolute “term” is a period of at least 15 consecutive days with less than 0.2mm of rainfall. Partial “term” is a period of at least 29 consecutive days during which the average daily rainfall does not exceed 0.2mm.

Xerophyte:

A plant adapted to live in dry conditions. Common adaptations include a reduction of leaf size, leaf hairs to trap a layer of moist air, water storage cells, sunken stomata and permanently rolled leaves that roll up in dry weather (e.g. marram grass).

Biofuels

Any fuel produced from organic (once living) matter, either directly from plants or indirectly from industrial, commercial, domestic, or agricultural wastes. Fossil fuel substitutes that can be made from from a range of crops including oilseeds, wheat and sugar.

Plantation:

A large farm or estate where one crop is produced commercially; such as palm oil in Malaysia or tea in Sri Lanka. They are usually owned by large companies, often multinational corporations. Many were established in countries under colonial rule, using slave labour.

Shifting Cultivation

A farming system in which farmers move on from one place to another when the land becomes exhausted. The most common form is slash-and-burn agriculture: land is cleared by burning, so that crops can be grown. After a few years, soil fertility is reduced and the land is abandoned. A new area is cleared while the old land recovers its fertility.

Deforestation

Destruction of forest for timber, fuel, charcoal burning and clearing for agriculture and extractive industries, such as mining. It causes fertile soil to be blown away or washed into rivers, leading to soil erosion, drought, flooding and loss of wildlife.

Soil Erosion:

The wearing away and redistribution of the Earth’s soil. It is caused by the action of water, wind and ice, and also by unsustainable methods of agriculture.

Ranching:

A commercial form of pastoral farming which involves extensive use of large areas of land for grazing cattle or sheep. They may be very large, especially where the soil quality is poor. In the Amazon basin, some deforested areas are used for beef cattle.

Arid

Areas that receive less than 250mm of rainfall each year.