Climate Characteristics (CIE IGCSE Geography)

World climate distribution

• Climates vary across the world. The reasons for these climate types include:
  • Latitude: with distance from the equator temperatures and sunshine hours decrease as the solar radiation is more dispersed at the poles and it has to pass through a greater amount of atmosphere
  • Altitude: Increases in altitude lead to decreases in temperature 
  • Continentality: locations further inland heat up more quickly in the summer and cool more quickly in the winter
  • Ocean currents: warm and cold currents circulate in the oceans either warming or cooling the adjacent land 
  • Aspect: in the northern hemisphere slopes facing south are warmer 
  • Prevailing winds: winds coming from warmer areas bring warmer air, increasing temperatures
  • Pressure systems: areas usually affected by low pressure such as the equator have rising air, condensation and cloud formation leading to more precipitation, whereas areas affected by high pressure have dry conditions due to the sinking air

Equatorial climate distribution

Distribution of the Equatorial Climate

Equatorial climate characteristics

Characteristics	Equatorial Climate
Location	Low latitudes Within the Tropics 23.5° north and south of the equator Amazon in South America, New Guinea, South-east Asia, Zaire Basin
Annual Precipitation	Over 2000mm
Temperature Range	low range of mean monthly temperatures - 26-28°C Constant high temperatures  Diurnal range is about 7oC
Seasons	No seasons - hot and wet all year round
Humidity	High, usually over 75-80%
Prevailing winds	Winds blow into the equatorial region from high pressure areas to the north and south.  The winds from the north blow from the north-east and the winds from the south blow from the south-east. The winds are known as the trade winds

Climate graph for Iquitos, Peru

Factors influencing the equatorial climate

• There are a range of factors which influence the climate including:
  • The midday sun is almost directly overhead all year meaning there is maximum insolation
  • Low pressure all year which leads to rising air, condensation, cloud formation and high precipitation levels
  • Dense vegetation cover leads to high levels of evaporation and transpiration 
  • The warm air stores large amounts of water vapour until the temperatures start to cool in late afternoon which then leads to heavy, daily convectional rainfall

Hot desert climate distribution

Distribution of the Hot Desert Climate

Hot desert climate characteristics

Characteristics	Hot Desert
Location	15° - 30° north and south of the equator (tropical and sub-tropical) North Africa - Sahara, Southern Africa - Kalahari and Namib, Australia. Middle East
Annual Precipitation	Below 250mm
Temperature Range	Daytime temperatures can reach 50°C but average around 25°C Night-time temperatures below 0°C Diurnal range is large up to 45°C Annual range is around 15°C
Seasons	Summer and winter
Humidity	Low often between 10-30%
Prevailing Winds	The winds are offshore blowing from the east across the land, so they do not collect any moisture

Climate Graph for Jeddah, Saudi Arabia

Factors influencing the hot desert climate

• High pressure all year which means the air is descending and warming so precipitation does not occur because the air is not rising
• Prevailing winds are often from over land masses which means they contain little moisture
• Some deserts are in a rain shadow so there is little rainfall
• Cold ocean currents on the west side of continents may reduce summer temperatures due to the cooling effect of the ocean

Influence of pressure systems

• Hot deserts form between 15^o- 30^o north and south of the equator as a result of the atmospheric pressure systems
  • Air rises at the equator and when it reaches the upper atmosphere it moves north and south
  • The air cools and starts to sink
  • This creates a zone of high pressure at about 30^o north and south of the equator
  • Due to the sinking air, warm air cannot rise, condense and form clouds. This results in high aridity

Atmospheric Pressure Systems