What is the difference between weather and climate?Weather is the current conditions in the atmosphere

Climate is the average weather conditions Measuring the weather conditions is a difficult task, so requires a wide variety of specialist equipment.

All of this material is kept inside an white wooden box, called a

‘Stevenson Screen’. These are specially designed so that the results are as fair as possible.

Design features include:

➡ Painted white to reflect heat so that the temperatures recorded aren’t artificially high➡Louvered sides allow air to circulate

➡Raised 110cm from the ground to prevent the ground from influencing the temperatures recorded➡Placed away from any other objects of buildings so that they do not influence the temperatures recorded

Within a Stevenson Screen you will find a variety of weather instruments.

Wea

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and

Cl

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Equipment Name Measurement

Cup anemometer Wind speed in kilometers (km)

Barometer Pressure in millibars (mb)

Wind vane Direction the wind is blowing from (compass points)

Wet and dry bulb thermometer (hydrometer) Relative humidity - percentage of moisture in the air (%)

Maximum-minimum thermometer Maximum and minimum temperature in degrees Celsius (°C)

Rain gauge Daily rainfall in millimeters (mm)

Types of Cloud

Cirrus CloudsMost common of high clouds, composed of thin wispy streams of ice. Usually white and predict fair weather

Stratus CloudsUniform grey clouds which cover the entire sky. These are associated with mist and drizzle

Cumulus CloudsWhite and fluffy clouds. These clouds grow upwards and can develop into cumulonimbus clouds

Cumulonimbus CloudsThese are thunderstorm clouds, which are associated with heavy rainfall and lightening

Presenting weather dataSynoptic Chart

A synoptic chart is any map that summarises atmospheric conditions over a wide area at any given time. They are used to give an overview of the weather conditions, using data from a number of weather stations and satellites.

By working together to create these maps meteorologists can work

together to make more accurate predictions.

There are many different types of weather map, but they all use the same

symbols which have been internationally agreed.

Weather symbols can seem confusing until you look for patterns.

To get a better picture

of the weather around

the world, weather

observations are takes

worldwide then plotted

on a synoptic chart

Types of Rainfall

1. Relief Rainfall

The shape of the land is called the relief. When the wind mets an area of highland it is forced to rise. As this air rises it cools and condenses to form clouds. These clouds bring with them rain, meaning that on one side of the mountain there will be heavy rain. As the wind then descends down the opposite side of the mountain, it warms and has now lost most of its moisture. This creates an area of low rainfall, called a rain shadow.

2. Frontal Rainfall

Rain can be created when two air masses meet. If a mass of cold air meets a mass of warm air the two are unable to mix. As the

Factors Influencing ClimateLatitude

At the equator the sun is directly overhead. This means that the sun’s rays are more focused, as they only have to heat up a small area of land. Where as at the poles the sun is at a lower angle in the sky, this means the sun’s rays are spread out over a larger area so cannot heat the ground enough to cause high temperatures.

Distance from the SeaThe sea is not very quick to heat up during the summer as

it is such a large volume of water. This means that places near the sea are often not as warm during the summer. However, the sea also takes a long time to cool down. This means that places near the sea are not as cold in the winter.Where as the land heats up very quickly but also cools down very quickly. Meaning that places inland have hot summers but cold winters.

Prevailing WindThe prevailing wind is the direction which the wind normally blows from. If it blows over an area of warm land the wind will be warmer, causing temperatures to be higher. The opposite is true if the wind blows over a cool area.Prevailing winds can also pick up moisture. So if the wind has blown over an area of

Types of Rainfall cold air is denser (heavier) than the warmair, it forces the warm air mass to rise and move over the cold air. As the warm air rises, it begins to cool and condense creating clouds. These clouds then bring with them rainfall.

3. Convectional Rainfall

Convectional rainfall is associated with warm climates. The sun heats up the ground causing any moisture in the ground or stored on leaves, etc to evaporate. This evaporated moisture rises and as it rises will cools. It then condenses to form clouds, resulting in rain.

The type of rainfall a place experiences will be determined by the location and the physical geography of the place.

water it will increase the levels of rainfall. Whereas if the wind has blown over a dry area then it will contain no moisture so rainfall will be very low.

Relief

Relief is the shape of the land, so how mountainous it is. This can affect the temperature as temperatures will face by 1°C for every 100 meters gained in altitude. Relief can also affect the levels of precipitation, with mountainous areas experiencing high levels of rainfall.

Ocean Currents

Ocean currents can have a dramatic effect on the climate of a location. These currents may bring warmer waters, which will result in a place experiencing higher temperatures than expected. For example, the UK is has a warm climate due to the North Atlantic Drift, which brings warm water from the Caribbean. Where as some places experience cold currents which lowers their temperature.

Climate graphs are

used to show the average rainfall and temperature experienced

in a particular location.

CLIMATE GRAPHS

Climate graphs are

used to show the average rainfall and temperature experienced

in a particular location.

Climate graph for the Sahara Desert

Presenting Climate Data

Climate is the average weather conditions for a particular location. This means that they calculate what the average temperature and rainfall for are in a particular location for each month of the year.This is then presented on a graph, where the temperature is shown as a line graph, and rainfall is shown as a bar graph. They are usually presented on the same set of axis, with rainfall on one side and temperature on the other then months of the year along the base.

Interpreting and describing climate graphs

•Look at the general shape of the graph. Does temperature rise and fall suddenly or is it more gentle? Does it change much throughout the year or is the line almost flat?

•Look for the extremes. What months have the highest and lowest temperatures and rainfall?

•Identify any patterns. Does the temperature and rainfall follow the patterns of the seasons?

•Work out the ranges in temperature and rainfall.

Climate graph for a deciduous woodland

Tropical RainforestsIn the tropical regions, either side of the equator, the

climate is very different. It is hotter and the temperatures remain high all year round. Although rainfall between the Tropic of Cancer and the Tropic of Capricorn can vary, within rainforest areas it remains especially high all year round. Rainforests not only receive a lot of rainfall but play a key role in the atmosphere, as 10% of the world’s rainfall depends on the rainforest putting water back into the atmosphere through evaporation and transpiration.

Although it is hot and wet for the majority of the year, temperature and rainfall are not evenly distributed. The sun is over the Tropic of Capricorn in December, meaning this tropic receives the maximum amount of sunlight. Whereas, the sun is over the Tropic of

Cancer in June so the temperature at the Tropic of Capricorn will drop slightly. All year the warm moist air rises to give low pressure and clouds, which combined with the prevailing winds, which blow from the oceans, means rainfall is high.

Vegetation in the Tropical RainforestRainforests are home to a huge variety and number of

plants. This is because the rainforests are an ideal environment

Rainforest Structure

Shrub LayerDue to the lack of light which

reaches the forest floor there is very little vegetation

between the trees

Under CanopyThere is limited sunlight,

saplings wait here for the

older plants to die, leaving a

space in the canopy which

they can grow into

CanopyWhere the upper parts of

most trees are found, the

canopy is home to most life found in the rainforest

EmergentsThe tops of all the tallest trees

in the rainforest

for plants to grow. They experience long hours of daylight which means that photosynthesis can take place all year round. As well as the long hours of sunlight, the temperatures in the rainforest rarely fall below 20°C, this means that plant growth is not limited by low temperatures. The rainforest also experience high rainfall each month so there is always enough water available for plant growth all year round. The high temperatures and rainfall combined allow for the rapid recycling of nutrients, which in turn encourages further plant growth.

Despite the ideal growing conditions found within a rainforest, there is very little vegetation found on the forest floor. This is because the floor can be prone to flooding, but the most important limiting factor is the lack of sunlight. As the canopy is so dense, very little sunlight reaches the forest floor, so growth is limited.

Nutrients recyclingRainforests are home to very fertile soil.

This is due to a process called nutrients recycling, whereby leaves which fall from the trees create a layer of leaf litter on the floor. Which along with any other organic matter is broken down by decomposers, returning nutrients to the soil. This process occurs very quickly in the rainforest due to the high temperatures and rainfall. These nutrients only remain in the soil for a short amount of time before they are absorbed by the trees and

used by the trees. This process is continuous, as trees in the rainforest lose their leaves all year round.

Although the soil in the rainforest is exceptionally fertile it is relatively thin. This means that the trees have very shallow roots which give very little support. To counteract this many of the trees will grow buttresses to help hold them in place.

Threats to the rainforestThere are a number of threats facing the

tropical rainforests globally. These have the potential to be catastrophic to not only on a local scale, but could cause damage globally.

The biggest threat facing the rainforest is that of deforestation. This involves large areas of forest being cut down by people so they can either sell the wood or use the land.

The most common method of deforestation is that of slash and burn. This is where most of larger trees are chopped down and sold to the timber market, then the plot is set on fire. This removes all the smaller trees and bushes in an easy way. The ash from the burning of the vegetation adds nutrients to the soil, which makes the land fertile and good for farming. However, because the nutrient cycle is then disrupted the soil soon becomes infertile and can no longer be used for farming without the use of fertilisers.

Madagascar is an island found of the coast of the east coast of Africa. It is off of coast of Mozambique, with the Mozambique Channel to the west and the Indian Ocean to the east. The island itself has a ridge of mountains which run down its centre.

Where is Madagascar?Madagascar is an island found of the coast of the east coast of Africa. It is off of coast of Mozambique, with the Mozambique Channel to the west and the Indian Ocean to the east. The island itself has a ridge of mountains which run down its centre.

Madagascar is home to a high number of endemic species, which means they are only found in Madagascar. This makes the rainforest here even more vulnerable, as if one species becomes extinct on the island this means it will be extinct worldwide.Madagascar also has a very complex food chain, so if numbers of one species, such as the Fossa, declines then the remainder of the food web may collapse.

Madagascan Rainforest

The rainfall within Madagascar is not evenly distributed, this is because most of the rainfall is relief rain. The prevailing winds come from the Indian Ocean, which mean they are full of moisture. As they blow across Madagascar they reach the mountains, at which point the air is forced to rise where it cools and condenses, producing high levels of rainfall. By the time the wind descends down the other side of the mountain it has

lost all of its moisture, meaning that the west coast of the island has very little rainfall (called the rain shadow). This is why the rainforests in Madagascar are found only in the east where the rainfall is highest.

Madagascar is the ninth poorest country in the world, so is classed as an LEDC. Most of the people are subsistence

Madagascar is called the ‘Great Red Island’ because the soil erosion washes all the red clay into the rivers and ocean turning it a muddy red. This a result of the slash and burn which is occurring on the island. As this leaves the soil exposed so during periods of rainfall it is easily eroded and washed away.

What are the threats?Madagascar is called the ‘Great Red Island’ because the soil erosion washes all the red clay into the rivers and ocean turning it a muddy red. This a result of the slash and burn which is occurring on the island. As this leaves the soil exposed so during periods of rainfall it is easily eroded and washed away.

farmers which means than they only grow enough food for their own consumption. As the population of Madagascar has grown so has the demand for farmland, meaning that more land has been cleared of rainforest to be used for farmland.

However, in recent years more and more land has been cleared not for subsistence farming, but for the farming of cash crops. Cash crops are those which are grown for profit purposes rather than for personal use. Madagascar produces a number of cash crops, such as coffee, tobacco and rice. These are then sold to the international market to bring money into the country. These provide 70% of overseas earning from exports; this is the main reasons why the forest is being removed so quickly. 90% of the original rainforest has already been removed, meaning the recovery of this ecosystem could soon be impossible.

Rainforest

cover is decreasing. What do you expect us to

do? We have to live. We need land to grow crops. We need

meat and skins so we have to hunt animals. Other countries want out

rice and coffee, so we grow it to earn money from abroad. This will

help our economy develop. You may care about the lemurs

but I care about providing for my family.

Hot DesertsDeserts are defined as any area that receives less than

250mm precipitation in a year. Deserts can be hot, for example the Sahara Desert in Africa; or cold, for example the tundra in North America.

Hot deserts are found in sub-tropical and tropical latitudes. They experience very high daytime temperatures, often over 50°C, and low night-time temperatures because of the lack of cloud cover to trap the heat within the lower atmosphere. They are mostly found on the western edge of continents due

to the prevailing winds in tropical regions are off-shore blowing from the east across the land, so cannot pick up any moisture.

Due to the heat of the sun, which is overhead at the equator, the land surfaces are warmed resulting in air rising. This rising air means that there is low pressure at the equator. This rising air cools and condenses to form thunderstorms, meaning equatorial areas experience very high rainfall. This creates a convection cell within the atmosphere, where the air rises at the equator and then moves north or south towards the tropics where it then sinks. These zones of high pressure (where the air is sinking) are associated with very low levels of rainfall and a large daily temperature range. This is because the air is sinking so there is no opportunity for any moisture

Rainforest Structure

Shrub LayerDue to the lack of light which

reaches the forest floor there is very little vegetation

between the trees

Under CanopyThere is limited sunlight,

saplings wait here for the

older plants to die, leaving a

space in the canopy which

they can grow into

CanopyWhere the upper parts of

most trees are found, the

canopy is home to most life found in the rainforest

EmergentsThe tops of all the tallest trees

in the rainforest

within the air to cool and condense.

Vegetation in the desertThere is very little vegetation within the

desert due to the lack of rainfall. Vegetation will be very sparse and plants will cluster in areas where the growing conditions are slightly better.

Vegetation found within deserts is highly adapted to the extreme conditions found in these locations. Many plants are low-growing so that they can avoid water loss as their

surface area is smaller. They also have small thick leaves or needles, like cacti, this means that less water is lost through evapotranspiration. Cacti also have a thick stem which can be used to store water, they can expand and store water during times of rainfall. Many plants also have long roots which travel horizontally to reach the maximum surface areas for water to find any surface moisture.

DesertificationOne of the major threats facing many

desert areas of the world is that of desertification. This is where soil is lost through erosion and the land becomes desert. There are a number of causes of desertification, ranging from physical to human in nature.

Periods of prolonged drought can result in the areas of land surrounding the desert into

desert themselves. This is because less rainfall means less water stored within the rocks and soil. Therefore many of the vegetation in the area cannot be supported and dies, leaving behind scrub and desert plants. As more and more of the soil becomes exposed it becomes more vulnerable to erosion. The lack of plants means there are few roots to hold the soil together, meaning that it can be easily eroded by the wind.

Human activity can also cause desertification. Population growth in regions surrounding deserts is causing the deserts themselves to expand. This is because more people demand more food and timber. This means that more crops (over-cultivation) have to be grown, which depletes the amount of nutrients within the soil. Until eventually there are not enough to sustain any vegetation, meaning that the soil will be left unprotected and open to erosion.

Likewise people will be forced to rear more animals, meaning more vegetation will be consumed (overgrazing) reducing the vegetation cover. Meaning the soil is left exposed and open to erosion.

Finally the demand for timber for firewood and building materials means there is more deforestation. This leaves the soil bare and unprotected, which means that it is more vulnerable to erosion.

All of these factors are resulting in the expansion of the worlds deserts through desertification.

The Sahara Desert is the largest hot desert in the world. It is found in the north of Africa, stretching from Western Sahara on the west coast to Egypt and Sudan on the east coast. It covers most of northern Africa spanning twelve countries in total.

Where is the Sahara Desert?The Sahara Desert is the largest hot desert in the world. It is found in the north of Africa, stretching from Western Sahara on the west coast to Egypt and Sudan on the east coast. It covers most of northern Africa spanning twelve countries in total.

Mali and the SahelThe Sahara is the world’s largest and hottest desert and

covers most of North Africa, it is roughly the same size as the USA. However, not all of the Sahara is covered by sand. Only 1/4 of the Sahara is covered in sand, known as ergs. The rest is gravel-strewn plains called reg or areas of barren rocks.

The Sahara is formed as a result of air on the equator being heated causing it to rapidly rise. This creates an area of low pressure. This air rises and then moves north and southwards towards the tropics. Once over the tropics the air sinks, as the air is sinking it is unable to condense and form clouds. Therefore creating areas of very little precipitation.

Today the Sahara is growing even larger, with the southern edge moving southwards due to overgrazing and deforestation through a process called desertification. This southern edge of the Sahara is called the Sahel, which is Arabic for ‘fringe’.

The Sahel is a semi-arid belt of dry soil approximately 500km wide. It stretches along the southern edge of the Sahara, separating it from the savanna grasslands.

The Sahel cannot be classified as a desert as it experiences an average annual rainfall of between 300-600 mm. However, when it does rain around 90% of this lost through evaporation.

The Fennec Fox is a mammal found in the Sahara. It is the world’s smallest fox but its perfectly adapted to life in these extreme conditions. It has enormous ears to help radiate heats to help it stay cool. It lives deep in the ground in long, cool burrows and emerges around dusk to hunt when the day is cooler.

The Acacia tree has adapted to life in the desert. It has a low shallow root system which allows it to find moisture. It has thorny leaves to prevent water loss through evapotranspiration and its crown is wide so the foliage can absorb the maximum amount of sunlight.