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Why does precipitation vary across Earth’s surface?
1. Water cycle
a) movement of water between the atmosphere and the Earth’s surface through evapotranspiration, condensation and precipitation
b) movement of water at different rates in the form of infiltration, surface runoff and groundwater flow
2. Relative humidity
a) condensation is affected by the amount of water vapour in the atmosphere
b) condensation occurs when the amount of water vapour exceeds the amount that can be held by the atmosphere at a given temperature
3. Clouds and precipitation
a) clouds form due to condensation nuclei and the coalescence of water droplets in the atmosphere
b) results in precipitation including convectional and relief rainfall
Which is the wettest area in Singapore in 2013?
Why do you think this part of Singapore receive higher amount of rainfall?
Do you believe in the video? Is it really wetter in the west? The highest hill we have is Bukit Timah is only 164m - would the air be cold enough to cause the condensation resulting in rainfall on the windward side?
Relative humidity
Graph showing how relative humidity changes with temperature throughout the day
· As temperature rise/increase from around 18°C at 6 am to around 31 °C at 6 pm, relative humidity fall/decrease from around 62% to 8%
· as temperature fall/decrease from around 31°C at 6 pm to around 18 °C at 6 am, relative humidity rise/increase from around 8% to 62%
Reminder:
If you are asked to describe from the diagram or graph, you must state the temperature and relative humidity at the different time of the day to show that you are making reference to it with the data.
Temperature affects relative humidity and not the other way round.
Reason:
· At higher temperatures, the air will be able to hold more water vapour.
As air molecules are more spread out, more water vapour can fill the spaces. Thus the relative humidity is low.
Therefore, assuming the actual water vapour in air is constant, relative humidity is lower at higher temperatures and higher at lower temperatures.. There is an inverse relationship between temperature and relative humidity.
Types of rain - Watch the videos on convectional and relief (orographic) rain below.
Which type of rain is common in Singapore? Give reasons for your answer.
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