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 Form 2 Geography Lessons on Climate

In this lesson we are going to discuss introduction to climate and the factors influencing climate

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Answer Text:
- Average weather conditions of a given place over a long period of time usually 30-35
Factors Influencing Climate
• It influences temperature whereby low latitudes have high temperature and high latitudes have low temperature
due to the angle at which the sun rays strike the earth and the distance travelled by the sun’s rays.
• It also influences rainfall whereby places in the equator receive rainfall in two seasons when the sun is overhead there while northern and southern tropical areas receive rainfall when the position of the sun is overhead in those areas.
Inter-Tropical Convergence Zone
It’s a low pressure belt around equator where trade winds converge.
It influences rainfall in the following ways:
• Places further from equator experience one rainy season when the sun is overhead and
a long dry season when the sun is in the S. hemisphere.
• Regions near equator have 2 seasons of heavy rainfall because they experience passage of ITCZ twice.
• It influences temperature whereby at low altitude temperature is high while at high altitude its lower due to
the thickness of atmosphere determining the number of particles to store heat and distance from space where
terrestrial radiation is lost.
• It also influences rainfall whereby mountains on the path of rain winds receive Orographic rainfall and the
windward slopes receive heavier rainfall than leeward slopes.
Distance from the Sea
• It influences temperature whereby places in temperate regions near the sea experience low temperature
during summer onshore winds blowing over cold ocean water and taking the cooling influence on adjacent land
because the water is heated at a slower rate than land.
• Places near the sea also experience higher temperatures during the winter or cool season due to sea
breezes carrying warmer air to the land because water loses heat at a slower rate than land.
• Temperatures in the interior of continents tend to be high in summer and very low in winter due to lack of marine
• It also influences rainfall whereby coastal regions receive a lot of rain when the winds are onshore and the
continental interiors receive less rain mainly in summer because onshore winds will have dropped most of
moisture along the way.
Ocean Currents
• It influences temperature whereby coasts which are washed by warm ocean currents are warmer while those washed by cold ocean currents are cooler due to the onshore winds being either warmed or cooled and then
taking the warmth or coolness to the land.
• It influences rainfall whereby coasts washed by warm ocean currents experience heavy rainfall
when moist onshore winds are warmed by the current and made to hold on to moisture which they release on
reaching the land.
• The coasts washed by cold ocean currents on the other hand experience low rainfall as a result of moist winds
being cooled and moisture in them condensed resulting in rain falling over the ocean thereby bringing little or no
rain to the coastal areas.
This is the cause of western margin deserts e.g. Kalahari and Namib deserts.
- Direction of slope in relation to sunlight and the rain bearing winds.
Its effect on temperature is more pronounced in the northern and southern hemisphere.
• In the N and S hemispheres the slopes facing sun are warmer while those facing away are cooler.
• The slopes in the direction of rain winds i.e. the windward slopes receive heavier relief rainfall than the leeward side.
Winds and Air Masses
Wind blowing from a warm region warms the region its passing over and if blowing from a cool region cools the
region it’s passing over since wind is a medium of transfer of heat.
• Sea breezes take cooling influence on land during hot afternoons.
• Katabatic winds cause low night temperatures on valleys and foot of mountains.
• Fohn and Chinook which are descending dry winds take dryness to the leeward sides of Alps and Rockies.
Winds influence rainfall in the following ways:
• Anabatic winds cause afternoon showers on mountainous regions.
• Moisture laden winds cause heavy rainfall.
• Persistent dry winds cause desert like conditions in the area they pass over e.g.
Harmattan winds from Sahara which blow over W. Africa.
• Regions around large water bodies experience high rainfall because of the effect of land breezes.
Configuration of Coastline
Coastal regions across the path of moisture laden winds receive higher rainfall because winds deposit moisture on land e.g. Mombasa while those lying parallel to the path of those winds receive less rainfall because moisture is deposited on the sea e.g. Lamu.
Forested areas experience a micro climate whereby:
• Temperature is lower due to shades of trees reducing solar insolation reaching the ground.
• Rainfall is heavier due to high rate of evapotranspiration and friction between trees and rain bearing winds.
Human Activities
• Man has caused deforestation in the process of creating room for settlement and agriculture which has
caused drop in rainfall amounts leading to semi-arid conditions.
• Man has constructed dams across rivers and done afforestation which has caused semi-arid regions to become
• Gases especially co2 emitted from burning fossil fuels and chlorofluorocarbons layer cause global warming through the greenhouse effect and destruction of ozone layer respectively