IGCSE and GCSE Weather, Climate and Ecosystems


2.3.1 Weather
Candidates should be able to:
• Draw, describe and explain the use and siting of the following instruments at a weather station: rain gauge, maximum-minimum thermometer, wet and dry bulb thermometer (hygrometer), barometer, anemometer and wind vane.
• Make calculations using information from these instruments.
• Have an awareness of simple digital instruments which can be used for weather observations.
• Use and interpret graphs and other diagrams showing weather data.
• Describe and explain the characteristics, siting and use made of a Stevenson screen.
• Describe the main types of cloud and be able to estimate the extent of cloud cover.

2.3.2 Climate
Candidates should be able to:
• Describe and explain the main characteristics of the climate in the regions listed in the syllabus (tropical rainforest and tropical desert): temperature – mean temperature of the hottest month, mean temperature of the coolest month, therefore the annual range; rainfall – the amount and seasonal distribution; other climate features – wind, cloud, humidity, etc. Factors influencing these characteristics should be noted such as latitude, pressure systems and the winds to which they give rise, distance from the sea, altitude and ocean currents. Candidates should be familiar with climatic graphs showing the main characteristics of temperature and rainfall of the climates in the regions listed.

2.3.3 Ecosystems
Candidates should be able to:
• Describe the characteristics and distribution of the two ecosystems listed in the syllabus (tropical rainforest and tropical desert).
• Explain the relationship in each ecosystem of natural vegetation, wildlife and climate.

2.4 Interrelationships between the natural environment and human activities
Candidates should be able to:
• Demonstrate an understanding that the natural environment presents hazards and offers opportunities for human activities. Reference should be made to the hazards posed by volcanic eruptions, earthquakes, tropical storms, flooding and drought. Use could be made of the study of contemporary examples to illustrate. This information would provide candidates with valuable case study information. Such examples could form resource material given in examination questions when candidates might be expected to illustrate inter-relationships between the natural environment and human activities from the data presented. Reference to the opportunities and problems posed for people could be incorporated when studies are made of the natural environment, for example the advantages and difficulties offered by river flood plains and deltas. The impact of human activities on the two ecosystems named in 2.3 should be considered.

Weather: The current state of the atmosphere in regards to temperature, cloud cover, wind speed and direction, precipitation, humidity, etc.

Climate: The average (general/normal) weather conditions that a region or country experiences. Climate is averaged over a number of years.

Weather Equipment




Stevenson Screen
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A Stevenson screen is basically a white louvered wooden box. The box is designed to contain some weather equipment like thermometers and barometers. The Stevenson screen is white to reflect sunlight and has slats to allow air to circulate easily. The Stevenson should be placed above the ground and away from the buildings. The idea is for the weather instruments to take accurate readings of the air, rather than direct sunlight or heat from the ground or from buildings. For more detailed information about the siting of a Stevenson Screen, read the attached document.

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Barometers are used to measure air pressure. Air pressure is normally measured in millibars. Barometers are normally kept inside Stevenson screens to keep them safe. A barometer has a movable needle (pointer). The pointer can be moved to the current reading so that you can then make a comparison with the reading from the following day.
Max./Min. Thermometer (sometimes called a Six's thermometer after its inventor)
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A maximum and minimum thermometer records the maximum temperature of the day and the minimum temperature of the day (diurnal range). A maximum/minimum thermometer contains a mixture of mercury and alcohol. The mercury sits in the u-bend of the thermometer. The bulb at the top of the tube reading the minimum temperature contains alcohol and the bulb at the top of the tube reading the maximum temperature contains a vacuum. On the minimum side the expansion of the mercury is restricted by the contracting alcohol, on the maximum side the expanding mercury can expand more freely into the vacuum. At any given time both thermometers should record the same temperature. However, during the day they would have recorded the maximum and minimum temperature - a steel marker should indicate these temperatures.
Wet/Dry Bulb Thermometer (hygrometer)
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A hygrometer measures the humidity of the air. Humidity is the amount of moisture (water vapour) in the air. A hygrometer has two thermometers, a dry one and a wet. Humidity is measured by using a table that looks at the difference between the wet bulb and the dry bulb. A hygrometer can also be used to find dew point. There is a difference between the dry and wet bulb thermometers because of latent heat created during the process of evaporation.
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Rain gauge
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Rain gauges are used to measure rainfall. Rainfall is normally measured in millimetres. Rain gauges should be placed on grass, because if they are placed on concrete, extra water can splash into them. Rain gauges should also be checked regularly to avoid evaporation.
Wind Vane
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Wind vanes are used to check the direction of the wind. Compass points are used to give wind direction. Wind is measured in the direction that the wind is coming from. Wind vanes are often placed on top of buildings so that they are fully exposed to the wind. When using a wind vane you need to use a compass to make sure that it is properly aligned.
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Anemometers measure wind speed. Wind speed is normally measured in mph or kph, but can also be measured in m/s (metres a second). Digital anemometers are very accurate, but the more basic plastic ones that many schools have aren't very good or accurate at recording light winds. Anemometers are normally placed on top of buildings so that they are not protected from the wind and so they don't experience channeling of wind e.g. if an anemometer was placed in a corridor where wind was forced through the readings would be higher than normal.
Cloud Cover
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It is also possible to count day light hours, sunshine hours or cloud cover. To Calculate day light hours you need to record the time between sun rise and sun set. To Calculate sun shine hours is a lot harder, because you have to time every time the sun comes out (stopwatch). To calculate cloud cover a mirror is often used. You divide the mirror into squares and then place the mirror on the ground. The mirror will reflect the clouds and you can count the number of squares covered or partially covered by cloud. You can do this as a percentage or convert to oktas which is the normal measurement of cloud cover. You have to take several readings to avoid anomalous results.

Climate Graphs and Weather Maps

Climate Graphs

Climate graphs show the average temperature and rainfall for a city or region over the year. Temperature is always shown in the form of a line graph. Some climate graphs have the average maximum temperature and the average minimum, others just have the overall average temperature. The line graph is normally coloured in red. Rainfall is always shown in the form a bar graph and normally coloured in blue.

Climate graphs are very good for showing averages, but they don't show anomalous years, because it is based on averages and it doesn't show things like the number of days of rain. A month may have 50mm of rain, but we don't know if that comes in small rain showers or one big thunderstorm.

When reading climate graphs you should look for trends and anomalies. On the graph below the temperature trend is fairly easy to read. It increases from January to July and then decreases until December. The rainfall data is not as straight forward because some of the early months fluctuate (go up and down). Whenever you are describing graphs, remember it is very important to use figures with the correct unit. Occasionally you maybe asked to give the temperature or rainfall range - this is the difference between the highest and lowest total.

Weather Maps

Weather maps can display a whole variety of data. The map below is fairly simple and simply shows:
  • Temperature
  • Wind speed
  • Wind direction
  • Likely weather e.g sun, rain cloud
Other weather maps can be more detailed and show information like:
  • Air pressure (using isolines to show areas of the same pressure (millibars))
  • Cloud cover (oktas)
  • Humidity (%)
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Weather - Clouds, Temperature and Rainfall


Clouds are a collection of water droplets or ice crystals. The warmer the air temperature, the more water vapour (gas) that the air can hold. However, when the air starts to cool, water vapour starts to condense as long as it has condensation nuclei to condense around.

  • Found high in the atmosphere – usually over 5,500 metres
  • Common throughout the world
  • Thin and wispy in appearance
  • Move fairly quickly

  • Low level – below 2000m and sometimes reaching ground.
  • Usually grey and colour and move fast.
  • Can produce light rain and snow.

  • Large clouds up to 10km high and across.
  • They resemble giant cauliflower.
  • Produce rain, thunder and lightening
  • Usually found in spring and summer

  • Fairly low clouds with bottom between 600m and 1200m
  • Look like lumps of cotton wool
  • Can produce light rain
  • Individual clouds have a short life cycle
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How to measure cloud cover?

Clouds are usually measured on oktas (0 oktas = clear sky, 8 oktas = total coverage). Students can do basic calculations by dividing a mirror into multiples of 8. They can then count the number of full or partial squares – convert to oktas e.g. if 6 out of 16 squares are filled then cloud cover is 3 oktas.


There are many factors that can impact temperature. The most common causes are below:

Latitude: Places in the tropics (between the Tropic of Cancer and Tropic of Capricorn) are much warmer than places furthest away near the poles. This is because the sun is more overhead in areas nearest the equator.

Distance from the sea: The sea takes longer to warm than land, so places near the sea are cooler in the summer because the sea cools them. However, the sea retains the heat better than the land so places near the sea are warmer in the winter because the sea warms them.

Prevailing winds: If the prevailing wind is from the poles then the temperature will be lower, but if the prevailing wind is from the tropics then the temperature will be higher.

Ocean currents: Ocean currents are classified as hot or cold. Hot ocean currents tends to warm winters and cold ones cool summers. The UK benefits from a warm ocean current travelling from the Gulf of Mexico.

Altitude: Temperatures on average decrease 1 degree Celsius for every 100 metres gained. This means that some places near the Equator e.g. the Andes in Ecuador can be covered in snow all year.
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Aspect: This is the direction that something faces. For example in the northern hemisphere south facing slopes face the sun and north facing face away from the sun. This means that in the northern hemisphere south facing slopes are warmer and ideal for growing things like grapes and olives.

Precipitation (types of rainfall)

Precipitation is any moisture that falls from the atmosphere. The most common types of precipitation are rain, snow, sleet, hail, fog and dew. Clouds basically form when water vapour (moisture) in the atmosphere starts to condense into water droplets. Water vapour starts to condense when the atmosphere can hold no more water i.e. it is saturated. Warm air can hold more moisture than cold air, so when air starts to cool water vapour is more likely to condense. Therefore, the formation of clouds and rain is most likely to happen when air cools. The three main types of rainfall are frontal, relief and convectional. However, it is important to note that water vapour must have condensation nuclei to condense around.

Condensation nuclei: Basically a surface that water vapour can condense on. This might be a piece of dust or a tiny grain of sand.
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Frontal rainfall: This happens when an area of cold air and area of warm air meet. The warm is less dense so is forced over the top of the cold air. As the warm air rises it starts to cool, as it cools it can hold less moisture so the water vapour starts to condense. The condensing water creates clouds and rainfall.

Relief rainfall: This happens when air runs into a mountain or hill. As the air meets the higher land it is obviously forced upwards. As it is forced up the air begins to cool, reducing the amount of moisture the air can hold and causing the water vapour to condense, creating clouds and rainfall.

Rain shadow: A dry area found on the lee side of mountains. A rain shadow gets below average rainfall because all the rain is deposited on top of the hills/mountains.

Convectional rainfall: This happens when the ground warms the air above it. As the air above the surface warms it becomes light and starts to rise. As it rises it starts to cool, as it cools it can hold less moisture and the water vapour begins to condense, creating clouds and rain. Convectional rainfall is very common in tropical countries and is more likely to happen in the afternoon once the air has had chance to warm, rise and condense.
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Air Pressure and Wind

Air pressure is simply the weight of air pressing down onto the surface of the earth. When air is warm it normally rises and creates an area of low pressure. When it is cool it sinks and creates an area of high pressure. Pressure is measured on a barometer. It is normally measured in millibars (mb). Areas of the same pressure are joined together on a map using isobars (isolines). Isobars look very similar to contour lines.

Air rises through the process of convection, it moves horizontally through the process of advection and sinks through the process of subsidence.

Wind is created by air moving from areas of high pressure to areas of low pressure. This can happen on a local scale or on a global scale, as shown in the diagram to the right. Theses global winds create cells, the three main cells are the Hadley, Ferrel and Polar.

All the cells operate similarly so I will just talk about the Hadley cell. Because of the hot temperatures near the equator, the land warms the air above which begins to rises. As it rises it is pushed out towards the tropics where it begins to cool slowly and sink. The sinking air then return towards the equator where there is low pressure. The rising air causes convectional rain near the equator. However, because of the rain over the equator the air reaching the tropics is very dry creating arid desert like conditions.

ITCZ: This is the inter-tropical convergence zone. Sailors give the ITCZ the nickname the 'doldrums'. It is an area near the equator where winds from the northern and southern hemisphere meet. Where they meet there is very little wind. However, even though there are limited winds the ITCZ has violent thunderstorms.
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Ecosystems: A biological environment consisting of all the living organisms within a particular area and the nonliving that interact with the organisms e.g. weather, soil, air and water.

Food Chains (webs)

A food web or chain shows the feeding connections within an ecosystem. Energy moves up the food chain or web. Food webs do not only contain animals, but also plants. Different animals rely on different food sources. Carnivores eat mainly meat, herbivores only eat vegetation and omnivores both. Food webs are very delicate and if you remove one piece then the whole web can collapse. This is true even if you remove the alpha (apex) predator. This is because the predator below in the food chain will enlarge in numbers and then eat the predator below it to extinction causing both to become extinct.

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Nitrogen Cycle

The nitrogen cycle is the recycling of nitrogen through the ground and atmosphere. Although 78% of our atmosphere is nitrogen, in its gaseous state it is not really useful to plant life so its conversion is extremely important. Plants absorb nitrogen through their roots so it is important that nitrogen is present in soil. Nitrogen in the atmosphere is converted to ammonia in the soil through the process of nitrogen fixation. Bacteria in the soil can then convert the ammonia through the process of nitrification into nitrates which can be absorbed by plants. Nitrogen that already exists in plants and animals is recycled by decomposers (mainly fungi and bacteria). If deforestation takes place then the recycling of nitrogen in the ground stops and the soil will become less fertile.
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Trophic Level: The position that an organism has in a food web. Producers are in the lowest trophic level and alpha predators in the top trophic level.

Autotroph or Producer: An organism that producers complex organic compounds from simple inorganic molecules using energy from the light or inorganic chemical reactions. Autotrophs are vegetation.

Heterotroph or Consumer: An organism that requires organic compounds in order for it to grow i.e. it needs to eat plants and/or animals.

Alpha or Apex Predator: The top predator with a food chain, the alpha predator is in the the top trophic level.

Carnivore: An animal that eats mainly or solely meat.

Herbivore: An animal that only eats vegetation.

Omnivore: An animal that eats both meat and vegetation.

Decomposer: Organisms that breakdown dead or decaying matter organisms. Decomposers are vital in the nitrogen cycle.

Human activities can disrupt or destroy delicate food webs. Disruptions may include:
  • Hunting of species for meat or parts e.g. skins
  • Deforestation can have multiple impacts including; loss of habitat, changes in the hydrological cycle, removal of organic matter, increased water erosion and removal of producers.
  • Mining which can pollute water course killing fish life and disturb other animals
  • Tourism which can disrupt animals and reduce their territory
  • Urbanisation and road building can destroy habitats, increase accidents, change the hydrological cycle and increase pollution and noise.
  • Dams can flood habitats and changing water courses from flowing to stationary

For IGCSE Geography you need to study two ecosystems; tropical rainforests and deserts. You need to look at their distribution, their climate, their vegetation and animals and threats to them.

Tropical Rainforests

Distribution of Tropical Rainforests

Tropical rainforests are found on or near the Equator (roughly between 28 degrees north and south). The main concentrations of tropical rainforests are:
  • The Congo Basin in central and west Africa
  • The Amazon in Brazil, Peru, Bolivia and Ecuador
  • SE Asia (Malaysia, Thailand, Vietnam, Indonesia and the Philippines)
  • Madagascar
  • North east Australia
  • Southern India and Sri Lanka
  • Central America

Remember when you are describing maps, if you can't remember the names of individual countries, then use compass points and continents. You can also use lines of latitude to help you describe as well as general locations e.g. inland or coastal.

Deforestation rates vary massively, one reason is the inaccessibility of many of the forests and the way people classify deforestation. However, it is claimed that now only about 5% of the earth's surface is covered in tropical rainforests, compared to nearly 15% 50 years ago. Many people believe that tropical rainforests could disappear this century.
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Deforestation: The removal (cutting down) of trees.

Reforestation: The replanting of trees once they have been cut down.

Afforestation: Planting trees in an area that previously did not have trees.

Importance of Tropical Rainforests

Reasons for Deforestation

Problems Caused by Deforestation

  • Biodiversity: Although rainforests cover only about 5/6% of the world's land mass, it is estimated that they could contain up to 50% of the world's biodiversity. This is potentially up to 15 million species.
  • Photosynthesis: Tropical rainforests are often referred to as the 'lungs of the earth' and convert large amounts of the greenhouse gas carbon dioxide back into oxygen. It is estimated that the Amazon rainforest alone produces about 20% of the earth's oxygen.
  • Flood control (interception, transpiration): Rainforests are an excellent natural measure to reducing flooding. There is leaf cover in rainforests all year so interception continually happens, extending rivers lag time. All vegetation uptakes water and transpires it.
  • Control of soil erosion: The root systems of trees and shrubs hold the very thin soil of rainforest in place. If trees are removed then both erosion of topsoil and landslides are more likely
  • Source of nutrients to humus layer in soil: The topsoil in rainforests is very thin and relies on the nutrients provided by rotting plants and animals. Because of the rainforests climate, there is a constant supply of leaf litter.
  • Medical remedies: Rainforests have been the source of many of today's drugs, including the basic ingredients for the hormone contraceptive pill, quinine (a anti-malaria drug) and curare (a paralysing drug).
  • Cash crops and agricultural products: Yam, coffee, rubber, mango, banana, sugarcane, cocoa and avocado were all first discovered in rainforests.
  • Ecotourism: With people becoming ever more environmentally conscious and looking for increasing adventures, ecotourism to rainforests is increasing. This not only helps protect rainforests, but creates income for locals. Ecotourism is an important income to countries like Costa Rica and Belize.
  • Home to indigenous groups: Although the number of indigenous groups and people have declined rapidly since colonisation in South America, it is estimated that there are still over 200,000 people that consider the Amazon their home.
  • Cattle Ranching: As the world's population gets bigger and richer, the demand for meat is increasing. To rear the cattle increasing tracts of the rainforest are being cleared to make pastures for grazing.
  • Subsistence Farming: Because of the large amounts of poor people that still live in tropical areas, subsistence farming is still widespread. Because rainforest soil loses its fertility quickly after deforestation, the most common form of subsistence farming is slash and burn. With growing populations this method of farming can cause widespread deforestation.
  • HEP: Many of the world's great rivers flow through rainforests e.g. the Amazon. These great rivers often have the most HEP potential. Unfortunately when a dam and reservoir are built it causes damage during construction, but also floods large areas.
  • Mining: With an ever increasing demand for the world's natural resources, countries and companies are looking at increasingly isolated locations, places like rainforests and Antarctica. The rainforests are believed to have many resources including metals and fossil fuels beneath their soils. Gold mining can be particular damaging as mercury is used in its extraction and often runs off into rivers.
  • Road building: Building new roads like Trans Amazon highway from Brazil to Bolivia not only causes deforestation itself, but its also opens up new areas to urbanisation, mining and farming causing further deforestation.
  • Urban growth: With the world population increasing as well as rates of urbanisation increasing many cities like Manaus in Brazil are growing rapidly causing deforestation.
  • Population growth: As populations grow, particularly in countries like Brazil, Peru, India and Vietnam that contain rainforests the demand for land increases, both to grow food and to live).
  • Plantations: Primary products are often seen as an income source for LEDCs, many of who have large areas of rainforest. At the same time with fossil fuels running out, alternative fuels sources are been searched for including biofuels e.g. Palm oil. This has lead to widespread deforestation in countries like Malaysia and Indonesia to plant cops like palm oil.
  • Timber (hardwoods): Hardwoods like mahogany and teak that take hundreds of years to grow are still in high demand to make things like furniture. The extraction of these trees can kills trees around them. Also many countries like China are also demanding large amounts of normal timber that are not always taken from sustainable sources.
  • Hunting: Hunting takes two forms, one form is for bushmeat to feed families and enough the sale of animals either alive e.g. parrots or dead for their skins e.g jaguars.
  • Flooding: Flash floods become more common after deforestation because there is less interception and less root uptake and transpiration. As such rainwater reaches the ground quick, saturating it and causing surface run-off and potential flooding.
  • Landslides: By removing trees and vegetation, you are making the soil less stable. Combine this with saturated ground and the likelihood of floods increases.
  • Biodiversity loss: Because all the species that live in the rainforest are not known it is hard to calculate species loss. However, scientists believe that 1 mammal or bird extinction can be extrapolated to approximately 23,000 extinctions.
  • Reduced photosynthesis: As more and more trees are removed the rate of photosynthesis reduces, releasing more carbon dioxide into the atmosphere and contributing to the greenhouse effect.
  • Silting of rivers: With increased flooding and surface run-off moil soils and silt is washed into rivers, this can not only change local ecosystems (water temperature and clarity) but can also reduce the depth of rivers making navigation harder.
  • Silting of seas and oceans: With the increased frequency of flooding and landslides more silt gets washed into the oceans. The increased amount of silts reduces the transparency of the sea reducing the light reefs receive and the temperature of the water. Increased silt can also block important shipping lanes.
  • Breaking of nutrient cycle: The top soil of rainforests is very thin an receives the majority of its nutrients from rotting flora and fauna. Be removing trees you also remove animals and therefore the source of the soils nutrients. With increased erosion the top soil (humus) layer is quickly washed away.
  • Sandification/desertification: Because rainforest soil loses its fertility very quickly after deforestation it quickly becomes hard to grow any vegetation on it, leading to sandification and possibly desertification.
  • Loss of indigenous homes: By clearing rainforests you are obviously destroying the homes of indigenous groups. But also moving close to indigenous groups can spread disease and alter local culture and traditions.
  • Reduced rainfall: Deforestation can lead to reduction in local rainfall because less water is intercepted and transpired from vegetation into the atmosphere reducing the formation of clouds and rainfall.
Problems and changes caused to rivers and drainage basins by deforestation include:
  • Increased sedimentation caused by increased surface run-off of sediment because of lack of vegetation holding soil in place. This will reduce the depth, wetted perimiter and cross-sectional area of rivers.
  • The above will cause greater erosion of topsoil
  • Less interception by trees causing the ground to become saturated quicker increasing surface run-off
  • Shorter lag time between maximum rainfall and maximum discharge because of less interception
  • An increase in flash floods because of less interception
  • Less transpiration from vegetation meaning that there will be less precipitation
  • Less precipitation will cause the discharge and velocity of rivers to decrease.
  • Increased pollution because water is no longer being filtered by vegetation and topsoil.

There are a number of different types of farming and harvesting that take place in rainforests. The main types are:

Hunter gathering: This is hunting wild animals and collecting (gathering) of wild fruits and nuts.

Shifting cultivation: Deforesting one area, growing crops in it for a number of years until the ground become infertile and then moving onto a new area.

Slash and burn farming: This is burning down an area of the rainforest to make way for farming. This is done for two reasons, one it clears an area quickly and two the ash fertilises the soil.

Land degradation: This is the reduction in the quality and quantity of soil. Soil in rainforests is actually very thin, so when you deforest plants and trees the soil is very vulnerable to erosion and loses its fertility quickly because its source of humus (rotting biological matter) is removed.

Fallow periods: This means not using (not growing) the land for a while. The aim is for the soil to regain some of its fertility. Shifting cultivators may return to areas of the forest after leaving it fallow for a number of years.

Tropical Rainforest Climate

Because tropical rainforests are close to the equator, they have very similar climates all year around. Their temperature is constant at between 25 and 30 degrees Celsius. They also receive rainfall all year around, although the monthly amounts may vary slightly. Tropical rainforests normally experience convectional rainfall. This is because they are close to the equator where temperatures are hot. The hot temperatures warm up the land, causing evaporation and transpiration and then convection. Not only is the weather similar between months, it is also very similar between days. Days will start of warm and then the temperature and humidity will build up. By the afternoon the air is saturated and tropical rainforest normally experience intense rainstorms. Because tropical rainforests are near to the equator the hot air rises causing low pressure.
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Tropical Rainforest Vegetation and Adaptation

Emergents: Emergents are tall trees that grow above the canopy layer in order to reach sunlight. Emergents can grow in excess of 50 metres.

Canopy: The canopy layer contains about 50% of the rainforests wildlife. The canopy layer is extremely thick and sits at between 25 and 35 metres.

Shrub Layer: The shrub layer is near the forest floor and is also extremely dense. Because the canopy is so thick the shrub layer has to adapt to survive in less light.

Lianas: These are woody vines that climb up other trees to try and get into the canopy and capture sunlight.

Strangler Figs: Strangler figs grow around the outside of other trees taking their light and nutrients and slowly killing the host tree. However, when the host tree collapses so does the strangler fig.

Butress Roots: Very long roots that are designed to support tall trees and to suck up the maximum amount of nutrients in fairly nutrient poor soil.

Fan Palms: Huge wide leaved plants that aim to capture as much sunlight and rainfall as possible.

Humus Layer: Rainforest soils are fairly infertile and dependent on the humus layer (decaying biological matter). If the source of humus is removed through deforestation then soils degrade very quickly.

Evergreen: Most vegetation in rainforests does shed its leaves once a year. However, because the climate of rainforests is similar all year, they shed their leaves at different times providing a constant source of biological matter and keeping the rainforest green.

Drip tip leaves: A lot of vegetation have leaves designed for rainfall to travel over them and drip to the ground. This is because the vegetation does not wanted to be damaged by large quantities of water.
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Tropical Rainforest Animals

Tropical rainforests have a huge amount of biodiversity within them - some estimates suggest that up to 50% of the earth's biodiversity live there (flora and fauna). The are many big famous mammals like tigers in SE Asia, jaguars in Central and South America and leopards in Africa. However, there are also much smaller mammals like sloths and primates like lemurs that live in rainforests. All mammals and primates have adapted in different ways to survive in the rainforest e.g. camouflage. As well as mammals and primates there are many other animals like birds, amphibians, reptiles and insects. Many rainforest animals are under threats. Threats include:
  • Habitat loss (deforestation)
  • Climate change (reduction in rainfall or increases in temperature)
  • Pollution (especially reptiles and amphibians)
  • Hunting (food food, skins and parts for Chinese medicine)
  • Cross breeding with domestic animals
  • Diseases (bird flu)
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Sustainable forestry: Forestry that does not cause permanent damage to any ecosystem and that can be maintained indefinitely (not damaging for future generations).

Protecting Tropical Rainforests

There are a number of ways to try and protect tropical rainforests, some of the most common are:

  • Creation of National Parks: More National Parks can be created to stop deforestation and loss of biodiversity. National Parks are areas of land protected by government law.
  • Rainforest Sales: Poor countries who make money from deforestation have muted the idea of selling their rainforests. One country which is hoping to do this is Guyana. This may include carbon offsetting where polluters can buy parts of the rainforest to offset some of the pollution that they are creating. (A Historic Move in the Battle to Save Rainforests - Guardian article)
  • Consumer Labelling (FSC): Consumer labelling can ensure that people only buy wood based products that have been taken from a sustainable source. The Forest Stewardship Council lends its label to products produced sustainably.
  • Sustainable forestry: Increase sustainable forestry, this would mean no destruction of rainforests because they take a long time to grow but instead the use of fast growing trees. Where deforestation is necessary in rainforests, possibly by indigenous groups, this should be selective cutting rather than clearfelling.
  • Ecotourism: The promotion of ecotourism gives tropical rainforests and biodiversity an economic value. If the value of tourism is greater than the value of selling trees and wild animals then locals will have the incentive to protect them.
  • Bans on Rainforest Products: There should be trading bans on endangered products from rainforests e.g. animal skins and hardwoods.
  • Education: Improved global education on the importance of biodiversity and tropical rainforests.
  • Global Initiatives: Global treaties like Kyoto which aim to reduce climate change should include greater protection for tropical rainforests which can actually reduce climate change.
  • Recycling (and reducing and reusing): If we reduce our consumption of wood based products as well as reusing them and recycling them then less trees need to be cut down to make them.
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Taman Negara Tropical Rainforest

Taman Negara is located in the middle of the Malaysian Peninsula. Malaysia is located in SE Asia and its capital city is Kuala Lumpar. Taman Negara is believed to be the World's tropical rainforest. It is home to a wide variety of important plants and animals including leopards, tigers and elephants. Malaysia still has large areas of rainforest, but some estimates suggest that it could reduce to 25% coverage by 2020. Deforestation in Malaysia has been caused by a number of things including:
  • Clearfelling to plant rubber plantations
  • Population growth and urbanisation
  • Clearfelling to plant palm oil
  • Industrial and recreational developments e.g. factories and golf courses
  • To sell timber for furniture

Most of Malaysia's early deforestation was clearfelling (the total removal of all trees) which is be far the most damaging basically removing an entire ecosystem. However, the Malaysian government has increasingly understood the importance of rainforests and has tried to protect. Some of the methods that they have used include:
  • Selective cutting: This is where only certain trees or groups of trees are cut down leaving the majority of the ecosystem intact.
  • Reducing the use of heavy damaging equipment and limiting the number of access tracks.
  • Increasing the number of National Parks and protected land.
  • Experimenting with helilogging to reduce impact on the rest of the forest
  • Increasing ecotourism which gives the forest economic value
  • Trying more urban forestry e.g. planting trees along roads
  • Encouraging villages to grow traditional local crops and become more self-sufficient

However, it must be remembered that any logging is going to have some negative impacts. Any logging will effect animals and also cutting one tree may inadvertently knock down other trees. Also the removal of hard words like teak and mahogany can never been sustainable because they can take hundreds of years to reach maturity. The most sustainable types of tree to log are fast growing varieties like pine. Scandinavia has many pine plantations where trees are replanted once cut. Pines from Scandinavia are popular because they grow slightly slower in the cold climate making them harder than normal and ideal for the construction industry.
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Distribution of Deserts

Deserts are located near the tropics (Tropic of Cancer and the Tropic of Capricorn). Some of the world's most famous deserts include:

  • Sahara in Northern Africa
  • Kalahari in Southern Africa
  • Atacama in South America
  • Gobi in Central Asia
  • Arabian in the Middle East
  • Great Victoria and Great Sandy in Australia
  • Mojave and Chihuahuan of North America

Antarctica is sometimes classified as a desert because it actually has very low levels of precipitation. However, when we talk about deserts in this section of the desert we mean sandy deserts.
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Desert Climates

Deserts are extremely dry (arid) places. True deserts normally have less than 250mm a year, although some deserts like the Atacama to the right can go years without any water. Deserts are very dry because the air that descends over them is very dry. The air is dry because most of the moisture has fallen as precipitation over the Equator (tropical rainforests) before being pushed out and falling near the tropics. The air is also very dry because the air travelling from the equator to the tropics travels over land and not the sea. This means that no additional moisture is picked up. Because there is no moisture in the air, there are very few clouds in deserts which means desert areas are exposed to high levels of incoming radiation from the sun. This means that daytime temperatures in the desert are very high. However, the lack of cloud cover also means that a lot of outgoing radiation is able to escape, making desert temperatures very cold at night. So even though the annual temperature range in deserts is very low, the daily temperature range is very high. The daily temperature range is known as the diurnal temperature range.
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Desert Fauna and Flora

Because of the very arid conditions found in deserts, both plants and animals have had to adapt to survive. Adaptations include:

Succulents e.g. cacti: Succulents tend to be fairly fat fleshy plants that are able to store water in their leaves, trunks and roots.

Ephemeral: These are plants with very short life cycles - typically 6-8 weeks. This means that they can take advantage of very short wet seasons in order to pollinate.

Long and wide roots: Plants in deserts have very long roots so that they are able to absorb the maximum amount of rainfall during periods of rainfall. It also makes them more stable in very lose soil.

Spiky and waxy surface: Many plants like cacti protect themselves with spikes and wax so that they are not eaten or damaged by animals.

Deserts don't have the same variety of animals as tropical rainforests, but many insects, reptiles and mammals have adapted to survive.

Nocturnal: Many animals will hide in burrows or behind rocks and vegetation during the hot daylight hours and only emerge at night.

Camels: Camels store fatty tissue in their humps which when metabolised actually releases water as well fat enabling them to survive in deserts.
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Even though deserts are very hot arid environments that normally have very low population densities, humans can still threaten them. Some of the threats caused by humans include:
  • Extraction of resources e.g. copper in the Atacama Desert
  • Hunting e.g. Oryx and Cheetah in the Namib Desert
  • Tourists damaging dunes e.g. dune boarding and desert bashing in the Arabian Desert
  • Overgrazing killing what little vegetation there is and overcultivation e.g. Southern Sahara
  • Deforestation: There is limited vegetation in deserts, but often it is removed for fuel or to make space for crops
  • Toyotarisation: 4X4 vehicles being driven across the desert disturbing animals, killing vegetation and creating dust storms

Desertification: The process of land turning into desert.

Land degradation: The reduction in the quality and quantity of soil.

Human Causes of Desertification

Physical Causes of Desertification

  • Overgrazing: Allowing too much livestock to graze on a piece of land which means all the vegetation is eaten making the ground susceptible to wind and water erosion.
  • Overcultivation: If you farm land to intensively and don't have fallow periods then all the nutrients in the soil get used.
  • Deforestation: Cutting down trees which not only means the land will be receiving less nutrients, but it also means it is more vulnerable to erosion because there is no interception and less stability because the root systems have been removed.
  • Overpopulation: As the world population continues to grow (now about 7 billion) the demand for agricultural products (crops and meat) is increasing, causing more land to be deforested, overcultivated and overgrazed.
  • Fertiliser and Pesticide Use: By using fertilisers and pesticides you can artificially increase yields of crops. However, the process is unnatural and prolonged periods of use can all naturally produced nutrients to be used and local water sources to become polluted reducing the ability of land to cultivate crops and therefore making it vulnerable to chemical degradation as well as wind and water erosion.
  • HYV and GM Crops: Like with fertilisers and pesticides, it is argued that HYV and GM crops have encouraged overcultivation, diminishing natural nutrients in the soil.
  • Unsustainable Water Use (aquifer depletion, unsustainable irrigation): If aquifers or rivers are used unsustainably then areas can become increasingly arid as water resources are used up. A classic example of unsustainable irrigation happened in the Aral Sea.
  • Toyotarisation: This is basically the increased use of 4x4s to travel across grasslands, deserts, etc. damaging topsoil and increasing wind and water erosion.
  • Rising Temperatures: As global temperatures increase it is becoming increasingly hard for vegetation to grow thus reducing vegetation cover and increasing the risk of wind and water erosion.
  • Falling Rainfall: As the amount of rainfall reduces in some areas like the Sahel, then it is increasingly hard for vegetation to grow again making the ground more vulnerable to wind and water erosion.
  • Flash floods: Intense periods of rainfall can also cause erosion of topsoil which leads to land degradation.
  • Wind: If a region is particularly windy then the amount of wind erosion is likely to increase.
For an example of desertification, you can use the Sahel again, which is the same case study that you used for as an example of famine in the agriculture section.

The Sahel - Desertification

The Sahel is an area of land south of the Sahara, running from Mauritania in the west, through Niger, Burkina Faso, Mali, Chad, Sudan and across to Ethiopian in the west. The Sahel is roughly 5,400km long and covers an area of about 3 million km2. The Sahel receives between 200mm and 600mm of rain annually. The vegetation is mainly savanna (grassland) with some areas of woodland and shrub land. The people of the Sahel are traditional semi-nomadic herders. In recent years the Sahel has been suffering from increasing soil degradation and desertification. The main reasons for increasing soil degradation are:
  • Population Growth (the population of the region is growing at about 3% a year and doubling every 20 years)
  • Deforestation (much of it caused by people collecting firewood)
  • Overgrazing (some of this is caused by loss of land to National Parks and tourist developments and commercial farms)
  • Colonialism - the creation of borders forced people more into villages making them less nomadic and placing greater pressure on the land.
  • Rising temperatures (greater evaporation) and reduced rainfall (droughts)
  • Storms - the rainfall that does take place tends to be in shorter more intense storms that can lead to water erosion.

Desertification has caused many problems in the Sahel including:
  • Famine
  • Dust storms
  • Conflict over diminishing resources

A number of solutions have been suggested to solve the problem of soil degradation and desertification including:
  • A giant shelter break (the Green Wall) - see article to the right
  • Population control
  • Finding alternatives to firewood e.g. solar cookers
  • Improved farming techniques e.g. reduced grazing numbers
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Great Green Wall to stop Sahel Desertification - Guardian article

Rays of Hope for Darfur's Refugees - Guardian article

Problems Caused by Desertification

Solutions to Desertification

  • Dust Storms: As soil become less stable because of the lack of vegetation it become much more vulnerable to wind erosion which can create large scale dust storms. Northern China is suffering from an increased frequency of dust storms as desertification takes place south of the Gobi Desert.
  • Reduced Crop Yields: As the soil becomes less fertile the amount of crops that it can support will reduce. The falling crop yields can lead to famine and starvation.
  • Conflict: With increasing soil degradation and reduction in agricultural output and available agricultural land conflict can arise over diminishing resources.
  • Famine: If the soil become degraded and cops begin to fail or the yields reduce in quantity then famine can happen. Famine is normally caused by a combination of factors, soil degradation, drought and possibly a natural disaster or conflict, so if soil degrades it increases the potential of famine.
  • Crop Rotation and Fallow Periods: Growing different crops each year, so different nutrients are used and to allow periods of rest (fallow periods) so that soil can regain its fertility.
  • Shelter Belts: Shelter belts (sometimes called wind breaks) are areas of forest or hedge that are left untouched to protect farmland from the affects of water and wind erosion. Shelter belts will often appear around the outside of fields.
  • Reforestation and Afforestation: By reforesting or afforesting areas you can help return land to its natural state, making it more fertile and stable, thus reducing wind and water erosion and ultimately land degradation.
  • Irrigation: It is possible to water areas of land that have become arid to try and improve the productivity of the soil. However, if water is not used sustainably then irrigation can cause water shortages and land degradation elsewhere.
  • Grazing Quotas: Placing limits on the number and types of animals that can graze on land, reducing the destruction of vegetation and eventual desertification.
  • Population Control: The main reason we are putting more pressure on the earth's resources (including soil) is because the world's population has reached 7 billion and is still growing rapidly. If we can control population growth then we can limit the amount of agricultural land we need and the intensity of our farming.
  • GM Crops: GM stands for genetically modified. GM crops can be engineered to withstand poor soil and water shortages. By growing some types of vegetation you maybe able to add nutrients back to the soil. However, it might it encourage people to farm on unsuitable land causing even further land degradation.

Tropical Storms

Tropical storms take different names in different parts of the world. In The Caribbean, US and Central America they are known as hurricanes, in the Indian Ocean they are known as cyclones and in the Pacific around the Philippines and Indonesia they are known as Typhoons. Tropical storms are normally found between the tropics near the Equator. The formation of tropical storms is not fully known, but scientists do know that they draw their energy from warm seas. Therefore tropical storms tends to happen in late summer when temperatures are warmest (over 27 degrees Celsius). Because tropical storms get their energy from the sea, when they do hit land they lose their energy quickly. Most tropical storms last between one and two weeks. The main hazards caused by tropical storms are:
  • Winds: Very strong winds up to 250km/hr accompany tropical storms. Strong winds can damage buildings, knock over trees and disrupt transport and communications
  • Flooding: Heavy rainfall is associated with tropical storms. Heavy rainfall actually causes much more damage and deaths than high winds.
  • Storms urges: Tropical storms moving in land can create storm surges and big waves. If tropical storms coincide with spring tides the impacts can be severe.
  • Landslides: Landslides are a secondary hazard. Landslides can be triggered when large amounts of rainfall saturate the ground increasing the stress on the slope.

Tropical storms are measured on the Saffir-Simpson Scale. The Saffir-Simpson currently has five categories, although some meteorologists believe a sixth category should be introduced to describe super hurricanes. Storms below 74mph (119kph) are described as only tropical storms. Anything above this speed is officially a hurricane/cyclone/typhoon.
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Landfall: This term simply describes when tropical storm hits land.

Formation: The time when an area of low pressure turns into a tropical storm.

Dissipation: The time when a tropical storm breaks up and loses all its strength.

The eye: The centre of a tropical storm.

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Typhoon Xangsane

Typhoon Xangsane was a category 4 typhoon that hits the Philippines, Vietnam (Southern Laos) and Thailand (SE Asia). The typhoon formed on the 25th September 2006 in the South China Sea off the east coast of the Philippines. It dissipated on October 1st 2006 over Vietnam, but the remnants off the storm went onto hit Thailand. The typhoon was very destructive causing a total of 279 deaths and $747 million in damages. Like with any destructive tropical storm the name Xangsane was retired and will never be used again to name a tropical storm.

In preparation for the arrival of Xangsane the Philippines closed all schools in its path, cancelled many flights in and out of Manilla and suspended other forms of public transport. In Vietnam 300,000 were evacuated from low lying areas and 2,400 boats ordered to return to port. Vietnam Airlines also cancelled or diverted flights. In Thailand residents were warned about possible flooding and landslides.

After the typhoon the Filipino Red Cross asked for $4.6 million. In addition 3,000 workers and 3 rescue teams were dispatched to the impacted area. The Red Cross also provided food and essential supplies to 6,300 families. In Vietnam the Red Cross also released emergency funds. The Vietnamese government released $6.2 million in aid money and donated 1,500 tonnes of rice. In Thailand the Red Cross gave emergency kits to 16,000 flood affected families.

Source: http://en.wikipedia.org/wiki/Typhoon_Xangsane

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