1. S4 – Weather Unit
Image copyright Joseph Kerski

2. Lesson 3 – Factors Affecting Rainfall
We Will:
Understand the four different factors which influence rainfall

3. STARTER – TRUE OR FALSE??
For every rise in altitude by 100m, the temperature decreases by 2°C
Temperatures drop the further an area is from the Equator due to the curvature of the earth
Oceans heat up and cool down much more slowly than land.
A warm ocean current called the East Atlantic Drift keeps Britain warmer than it would otherwise be.
False
True

4. What do you notice about the rainfall in Scotland?
Glenfinnan
More specific data can be found here -
What is the rainfall where you are?
Glenfinnan is one of the wettest places in the UK. It rained 1773 mm in the year 2017!
In Inverness it was 690 mm.
This is a Choropleth map. It uses colour to show the differences in rainfall across Scotland.
What do you notice about the rainfall in Scotland?

5. Think, Pair, Share
Why does the west of Scotland receive much higher rainfall than the east?

6. Let’s look at a cross-section of Scotland across the Great Glen from Fort William to Inverness.FW
Question pupils about any other records in Fort William they know about. Hopefully they will bring up Ben Nevis as the highest mountain. Ask if there might be link between the high rainfall and high landscape……. FW
INV

7. 1. Relief Upland areas receive more rain than lowland areas.
Relief Rainfall (or Orographic Rainfall) In Geography, relief means the height of the land.
1. Relief Upland areas receive more rain than lowland areas.
As the air rises, it cools. Eventually it reaches the temperature at which there is more condensation going on than evaporation (try to avoid talking about how much moisture the air can hold) at which point cloud droplets start forming. These combine until they are large enough to fall as rain. After the air has passed the top of the mountain, it sinks down the side of the mountain, warming as it sinks. However, as the rainfall removed so much moisture from the air, it is now much drier than it was upstream.

9. Rain Shadow
Himalayan Rain Shadow

10. Relief Rainfall Copy the diagram in to your jotter.AO FW BN I NS FA
AO – Atlantic Ocean
FW – Fort William
BN – Ben Nevis
FA – Fort Augustus
I – Inverness
NS – North Sea
Now add the following labels onto your diagram: - Warm moist air is forced to rise over high land.
- As the air rises it cools and water vapour condenses.
- Clouds form and precipitation occurs.
- The drier air descends and heats up.
- Any water droplets in the air (e.g. cloud) evaporate
Name the places marked with a

11. Explain what you think is happening in the following diagram
Use alongside the convection rainfall worksheet
Explain what you think is happening in the following diagram

12. Frontal Rainfall
Brief introduction. This will be covered when we begin pressure systems. A front is where two different temperatures of air meet.

13. Plenary
Look at the satellite image of South America. Where do you think the wettest/driest places are? Video Clip