CLIMATE GRAPHS
Climate Graphs are very useful in comparing the annual temperature
and rainfall of places around the world. They are very easy to plot and
read. The simple steps below should show you how to draw one and
then how to read it:
1. Draw the axis of your graph, with the months of the year along the
bottom, the amount of rainfall on one axis, and the temperature on the
other axis.
2. Plot on the rainfall as a bar chart, coloured blue.
3. Plot on the temperature as a line graph, coloured red.
4. Finish it off by including the following:
o The total rainfall for the year (add all the bars together)
o The temperature range (the difference between the highest temperature
and the lowest one).
o The name of the place that the graph is for.
The global distribution of climate
Climate describes the temperature, precipitation, and other weather
conditions of a certain area. The climate of an area describes how these
variables may be over a long period, for instance the South of France in
the summer is hot and dry.
However this is not always the case as there are some days when it is
raining and fairly cool. These daily changes do not affect the overall
climate of the area, and are described as the weather of the area for that
day.
The map below shows the main climatic regions of the world:
1|P age
Factors affecting climate
Many factors affect the climate of different areas around the
world. Themain ones are described below:
Altitude: Temperature falls the higher youare. The loss in temperature is
approximately 10°C for every kilometre yourise. This fall in temperature
with height is due to the fact that the airat higher altitudes is thinner.
There are fewer molecules available to receive and retain heat. Wind
chill may also mean that the temperatures inupland areas are lower than
expected.
Aspect: This relates to the direction in which a place is facing. Aspect
only really affects local climate, not global ones. In the Northern
Hemisphere, south facing slopes receive far more sunlight than north
facing ones. These are therefore much better for agriculture and often
settlement will locate there due to the better aspect.
2|P age
Distance from the Sea: The sea can have agreat influence over climates
in maritime regions. The sea takes much longer to heat up but retains that
heat far better than the land. Consequently the land is often warmer than
the sea during the day, however the situation is reversed at night.
This means that places like Britain, which are near the sea, have relatively
cool days and warm nights, as well as warm summers and mild winters.
The influence ofthe sea diminishes as you move further inland, for
instance to central Europe, where warmer winters and cooler summers
will be experienced.
Latitude: on global climates. Lines of Latitude are those that run
horizontally around the world. The most famous line of latitude is the
Equator. Using the lines of latitude we can easily divide the world in to
specific climatic sections.
3|P age

Between 23.5 South and 23.5 North is the region called thetropics. These
receive the most heat from the sun because itis almost directly overhead
and so the solar radiation does not have to travel through very much of
the atmosphere. It heats a very concentrated area of the surface of the
ground.

Between 23.5 and 66.5 in both the Northern and Southern Hemispheres
are the temperate regions. These have reasonably hot summers and mild
winters.

Above 66.5 in both hemispheres are the Polar Regions, which are very
cold. They receive sunlight for only half the year due to the angle of the
Earth on its rotation. During the months when they do have sunlight, it
travels to them at a very shallow angle, meaning that it has to travel
through a lot of the atmosphere and has to heat a wide area of the surface.
Ocean Currents: Many areas beside the sea are affected by ocean
currents. These can be either warm or cold currents. The United Kingdom
is directly in the path of the Gulf Stream and the Northern Atlantic
Stream, which bring warm water from the Caribbean across the Atlantic
to our shores. This current alone is the reason why our climate is mild
compared to places of similar latitude like Newfoundland.
Prevailing Winds: The prevailing (most common) wind in the United
Kingdom comes form the South West. If a prevailing wind travels over a
4|P age
warm surface it will bring warm weather, whilst if it travels over a cold
surface it will bring cold weather.
The south-westerly winds in Britain travel across the Atlantic. In the
summer this means that the air is cooled, whilst in the winter the water
warms the air, bringing warmer winters than we might expect.
RAINFALL
There are three common types of rainfall, all of which occur in the United
Kingdom. All have the common theme of air being forced to rise.
As air rises it cools it cannot hold as much moisture as it could when it
was warmer. Eventually the rising air reaches a point where it is 100%
saturated, in other words it cannot hold any more water. This is
called dew point, and it is above this point that condensation occurs.
Condensation is the process by which the water vapour (a gas) held in
the air is turned back into water droplets (a liquid), which fall as rain.
Convectional rainfall
Very common in areas where the ground is heated by the hot sun, such as
the Tropics. This is why those areas experience heavy rainfalls most
afternoons. The United Kingdom does experience some convectional
rainfall during the summer, particularly in the South East of the country.
Convectional rainfall occurs when:

The surface of the earth is heated by the sun.

The warm surface heats the air above it. Hot air always rises so this
newly heated air does so.

As it rises the air-cools and begins to condensate.

Further rising and cooling causes a large amount of condensation to occur
and rain is formed.

Convection tends to produce towering cumulo-nimbus clouds, which
produce heavy rain and possible thunder and lightning.
5|P age
Frontal rainfall
The United Kingdom experiences a lot of frontal rainfall, as it is
associated with the movement of depressions over the country, which are
described in more detail elsewhere in this topic.
Frontal rainfall occurs when:

Two air masses meet, one a warm air mass and one a cold air mass.

The lighter, less dense, warm air is forced to rise over the denser, cold air.

This causes the warm air to cool and begin to condense.

As the warm air is forced to rise further condensation occurs and rain is
formed.

Frontal rain produces a variety of clouds, which bring moderate to heavy
rainfall.
6|P age
Relief rainfall
This is also called orographic rainfall, which is very common in the
United Kingdom, especially on the West coast since the prevailing
weather comes from that direction.
Relief Rainfall occurs when:

The prevailing winds pick up moisture from the sea as they travel across
it, making the air moist.

The moist air reaches the coast and is forced to rise over mountains and
hills.

This forces the air to cool and condense, forming clouds.

The air continues to be forced over the mountains and so it drops its
moisture as relief rain.

Once over the top of the mountain the air will usually drop down the
other side, warming as it does so. This means it has a greater ability to
carry water moisture and so there is little rain on the far side of the
mountain. This area is called the rain shadow.
7|P age
DEPRESSIONS & ANTICYCLONES
To understand the concept of depressions and anticyclones, we need to
understand the terms atmospheric pressure, high pressure and low
pressure.
We all know that air exerts pressure and atmospheric pressure is
nothing but the force exerted by the air on the earth. To understand
properly, look at the diagram given below.
Concept
of
depressions
and
anticyclones
Pressure is highest at sea level and decreases with increase in altitude.
Also, earth consists of various high and low-pressure areas which control
the weather around the world.
How low and high pressure is formed?
Rising of air causes low pressure. In simple terms, the rising air leads to
less air on the surface means low air particles pressure. On the contrary, if
the air moves down towards the surface, it means there will be more
density of air particles leading to high pressure.
Easy way to remember – Taking out books from your bag (equivalent to
rising of air) leads to low pressure on your shoulders while putting more
books inside your bag (air towards the earth) will put high pressure on
your shoulder.
Just remember that low-pressure areas create rains and storms while
the high-pressure area leads to clear skies.
8|P age
Now that we have understood the concept of low pressure and highpressure area, it is easy to understand the phenomenon of depressions and
anticyclones.
Depressions
The hot air tends to rise while cold air settles down. Therefore when the
hot air from the land rises, it forms the area of low pressure on the earth.
This area of low pressure is called Depression.
The air moves from high pressure to low pressure hence the depression
region get more wind circulation as compared to high pressure areas. The
upward and inward circulation of wind is rapid in the low-pressure
region.
Depressions
As the air rises from the surface and cools, it forms clouds and eventually
leads to precipitation, often in the form of heavy storms. Thus,
depressions are responsible for the generation of cyclones.
How it affects the weather of UK?
The low-pressure systems often begin in Atlantic, moving eastwards
toward the UK. These are responsible for the UK’s changeable weather.
In winters they form snow storms, and in summer it causes floods and
heavy rainfall.
Warm air migrating north from tropics meet cold dense air migrating
south from the polar region.
9|P age
The warm air is cut by advancing cold air, and because it has more
energy and lesser density than cold air, it is forced to rise above at a cold
front.
Further, warm air advances into the cold air and is also forced to rise
above this denser cold air at warm front.
At both fronts, air is rising to lead to cooling and condensation which
eventually results in the rain at both fronts.
The rising air forms low pressure at the earth’s surface at the centre of the
storm. Air moves in from higher pressure areas around the depression
(lower pressure area) giving the high winds that we often associate with
the depressions.
Overall impact of depression
 It causes damage to the economy of the country, farming, and
tourism.
 Disturbance in transportation.
 Disruption of water supply and electricity.
 Effect on farming leads to a price hike in supermarkets.
 Damage of grasslands.
 Drowning of small animals.
 Landslides
 Destruction of the habitat of wild animals.
Interesting Fact – 2007 in the UK was the wettest since records began in
1766 caused by Atlantic depression. It leads to serious flooding in
Midlands, southern England, and Yorkshire.
NOTE – The pattern of the wind direction in cyclones depends on the
rotation of the earth. In northern hemisphere in the conditions of low
pressure or depression, the wind moves anticlockwise while the direction
of the wind is clockwise in anticyclonic (high pressure) conditions. This
is due to the Coriolis force of the earth or simply due to the rotation of the
earth.
Northern hemisphere
10 | P a g e
Anticyclones
Anticyclones are formed in the area of high pressure. It is formed when
wind sinks towards land. The sinking of air is due to the formation of a
convergence zone at a higher altitude. As the air cannot move upwards, it
is forced to move downwards. As the air hit the earth’s surface, it
diverges in different directions. The divergence is due to the tendency of
the winds to move from the high-pressure area to low-pressure area. Due
to this divergence, these winds do not carry the moisture with them to be
able to form clouds. Thus, anticyclones leads to clear skies.
Anticyclones
How anticyclones affect the weather of UK?
In winters, a stable atmosphere and light winds due to anticyclonic
conditions can lead to fog and frost. The fall of temperature is due to the
clear skies which allow the heat to be lost from the surface of the earth
through radiation. Further, light winds encourage the formation of fog.
As the sea surrounds the UK, the air is often moist. The fast cooling
ground cools and condenses any moisture in the air, forming droplets of
ice when the temperature falls below freezing forming frost.
In summers, anticyclones bring warm, long sunny days with them.
Though anticyclones make the weather dry but sometimes when the
temperature get too high, it can lead to thunderstorms. Generally,
anticyclones bring warm and fine weather for the UK and nearby
continents.
Anticyclones in winters can cause haze and fog interrupting clear vision
and thus affects transportation and daily activities.
11 | P a g e