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How do you model a bushfire?

By David, 13 September 2017 Activity

a bushfire

Image: Wikimedia commons/80 trading 24 CC-BY-SA

Bushfires are destructive and dangerous. They can be fickle, but scientists are developing ways to predict their behaviour. This activity shows you one way that a scientist might think about bushfires.

You will need

  • Pencil
  • Paper
  • Coin

A simple simulation

  1. Draw five adjacent squares.
  2. five squares - the first has a fire, ad the last has a houseDraw a fire in the first square, and a house in the last one.
  3. Read the instructions below, and before you run the simulation, make a prediction – do you think the house will burn down?
  4. To run the simulation, start by looking at the edge between the fire box and the next box.
  5. A coin showing heads and someone drawing a fireFlip a coin.
    • If it’s heads, the fire spreads – draw fire in the next box.
    • If it’s tails, the fire doesn’t spread. Put an x on the edge between the two.
  6. a coin showing tails and someone drawing an xIf the fire did spread, you can flip again to see if it spreads to the next box, and so on.
  7. Did the house burn down? Was your prediction right?

A more complicated example

Forests aren’t usually shaped like a line – they cover areas. And that means fire can spread north, south, east or west. So let’s try a slightly different simulation.

  1. Draw a grid of boxes, three boxes high and five boxes wide.
  2. Draw a fire in the first box of the middle row.
  3. Draw a house in the last box of the middle row.
  4. Read the instructions below, and before you run the simulation, make a prediction – do you think the house will burn down?
  5. Someone is pointing at an edge of a grid of boxes.To run the simulation, start by looking at an edge between a fire box and an empty box.
  6. Flip a coin.
    • If it’s heads, the fire spreads – draw a fire in the next box.
    • If it’s tails, the fire doesn’t spread. Put an x on the edge between the two.
  7. Then look for another edge between a fire box and an empty box, one that doesn’t have an x on it.
  8. Someone is drawing a fire on a picture of a houseYou can finish the simulation in two ways:
    • The house burns down or
    • There’s an x on all the edges where the fire could spread.
  9. Did the house burn down? Was your prediction right?

What’s happening?

This is a very simple simulation, but it’s based on real science. Many bushfire simulations work on a grid system, and use probabilities to work out whether the fire will spread further. However, they also take into account real world factors such as wind speed, temperature and the amount of vegetation.

In the first simulation, the house is pretty safe. The only way for it to burn down is if you get four heads in a row, which has only about a six per cent chance! But that doesn’t mean it’s completely safe – when we tried the first simulation, the house burnt down on the first try.

The second simulation should be more likely to burn down the house, because there are more paths for the fire to follow. Each fire square has more neighbours to spread to, so there is more chance the fire will continue to burn. The house is still relatively safe, though – it took us 10 attempts for it to burn down.

The fire would be more dangerous again if you tried running a similar simulation on a grid of hexagons. Hexagons have six neighbours where squares only have four. That means a hexagon grid is more connected, and the fire will spread further and faster.

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