Humidity and Rainfall

Humidity and Rainfall

1. Relative Humidity

   • a.k.a RH
   • proportion of water vapour in the air inrelation to the maximum amount of air can hold at a given temperature
   • expressed as percentage
   • saturation is 100% RH
   • saturation occurs when there is max amout of water vapour in the air
   • Evaporation is not possible when the air is saturated

2. Precipitation

   • refers to any water falling from the atmosphere to the earth's surface
   • 2 types of rain : convectional and relief rain
   • 1. Clouds are made up of water droplets
   • 2. These water droplets combine to form big water droplets.
   • 3. The big water droplets became too heavy and fall as rain.

3. Convectional rain

   • 1. Intense insolation -> rapid evaporation
   • 2. Large quantity of water vapour rises rapidly -> condensation -> clouds
   • 3. Cumulonibous clouds -> anvil / mushroom shaped
   • 4. Heavy downpour over a short duration within a small area, thunder and lightning are common

4. Relief rain

   • Occurs when heavy moist air is forced up a landform of higher altitude by winds
   • 1. When moist air rises, the surrounding temperature falls -> rising RH and promotion of condensation
   • 2. Clouds cannot hold the heavy water droplets -> rain on the windward side
   • 3. clouds pass over the mountains, most moisture released -> dry air
   • 4. Leeward side -> no rain -> rain shadow

5. Atmospheric pressure

   • Atmospheric (air) pressure is the weight of the air exerted on the earth"s surface
   • Dependent on temperature and altitude
   • Lower temperature -> air molecules packed closer -> greater weight exerted per unit are -> higher air pressure
   • Low land -> low altitude -> more air above -> higher air pressure
   • Movement of air from high pressure to low pressure

6. Land and Sea breezes

7. Climate types

   • Tropical/Equatorial climate
     • Found within 10 degrees of Equator
     • Natural vegetation : Tropical rainforest, mangroove
     • High mean annual temperature of 27 degrees
     • No distinct wet or dry season -> rain throughout the year
     • Relative humidity of >80%
     • High annual rainfall of 150 to 300cm
     • Convectional rain is common
   • Polar climate
     • Summer temperature is about 5 to 10 degrees
     • Winter temperature stays below -15 to 20 degrees
     • Large annual temperature range
     • Precipitation - mainly snow, only rain in short summers
     • Polar climate cover 20% of Earth
     • Lack warm summers, have long winters
     • Days are short, nights are long
     • Strong cold winds
     • Treeless tundra, very little vegetation
   • Cool temperate climate
     • Found within 35 to 70 degrees
     • Large variation in climatic data
     • Low mean annual temperature o 5 to 10 degrees
     • Large annual temperature range of 20 to 30 degrees
     • Strong maritime effects on coastal areas
     • Low moderate annual rainfall of 30 to 200 cm
     • Precipitation -> rain and snow

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