Lesson 1: What are the causes of wildfires?
Learning objectives:
To be able to define the term 'wildfire'.
To be able to describe the location of areas in which wildfires are common and explain why they happen here.
To be able to give and explain at least 5 causes of wildfires.
Wildfires are unplanned, unwanted wild land fires, including unauthorised human-induced fires. They are sometimes known as bushfires in Australia and brushfires in the USA.
Wildfires are a common occurence in some parts of the world. They occur on every continent except Antarctica. They happen most frequently in hot areas where there are extended periods of drought. Fires need heat, fuel (eg. dried out vegetation) and oxygen to continue to burn. High temperatures can preheat fuels in the fire's path so that they burn more readily. Strong winds can fan the flames, pushing them towards new fuel sources as well as transferring burning embers and sparks which can start spot-fires. During the day, the sunlight heats the ground and warm air rises. When hot air currents travel up sloped landscapes they can cause fires to start.
Forest fuels consist of ground, surface and aerial materials.
Ground fuels lie below the earth's surface eg. tree roots.
Surface fuels include twigs, grasses, wood and needles.
Aerial fuels include tree crowns, branches and hanging mosses.
The map below shows the global distribution of wildfires in August and February 2008. The maps show different patterns for the two times of year. In AUgust, the fires were concentrated in two areas - just north of the Black Sea in Romania and the Ukraine and in a band across the African continent at about 15-20 degrees south of the equator. The map for February shows a concentration in Venezuala (in the north of South America) and in a band across the African continent at about 10-15 degrees north of the equator.
Why do wildfires happen?
The causes of wildfires can be divided into 2 categories - natural and human. WIldfires are not like the other hazards that we have studied because, unlike earthquakes/volcanoes/storms, people can cause wildfires. Experts have suggested that 90% of wildfires are actually caused by people.
Natural causes of wildfires
Lightning is the single biggest natural cause of wildfires. Most fires started by lightning are small and burn out quickly but if the conditions are right then fires started by lightning can spread very rapidly. About 8 million lightning strikes hit the earth every day!
Spontaneous heating is where material becomes heated to the point at which it catches fire without a spark. This is common wherelots of leaves and branches have fallen to the ground and not been cleared away - the flow of air is restricted and often leads to fire.
Volcanic eruptions give out red hot lava and ash whch can start wildfires.
Wildfires are more common on south-facing slopes because the sun dries out the vegetation. Steep slopes also help fires to spread as the flames hit the upslope vegetation.
Human causes of wildfires
There are many human causes of wildfires including...
Arson - deliberate fire-starting. This is illegal.
Sparks for train wheels or from machinery
Military training
Household chimneys
BBQs and camp fires which haven't been extinguished properly
Broken bottles acting as a magnifying glass and concentrating the sun's rays
Slash and burn farming techniques (particualrly common in Brazil)
Discarded cigarettes
Children playing with matches
Electricity pylons falling down in high winds
Useful links:
Interactive about the sources of fire
US active fires - updapted in real time
How Stuff Works - Causes of wildfires
Lesson 2: What are the effects of wildfires?
Learning objectives:
To be able to classify the effects of wildfires into social, economic and environmental.
To be able to classify the effects of wildfires into primary and secondary effects.
The effects of wildfires can be classified using either the primary/secondary categories or the social/economic/environmental classification. Make sure that you can use both systems. Remember, a good geographer must open his/her eyes to SEE the world (social, economic, environmental). Social effects are those affecting people. Economic effects are those affecting money and business. Environmental (physical) effects are those affecting natural and built materials.
Primary effects of wildfires
Loss of life and injury to people and animals who are caught in the flames.
Destruction of property and possessions (this is getting more severe as more and more people live in the urban-rural fringe)
Burning of vegetation and crops.
Huge amounts of smoke released.
Secondary effects of wildfires
Health problems for people as a result of the smoke and ash.
Loss of jobs and incomes for agricultural workers whose animals/crops are destroyed.
Decline in the tourist industry, leading to loss of jobs.
Homelessness.
Insurance premiums rise.
Access to recreational areas is restricted.
Soil erosion and landslides because there is less vegetation to bind the soil together.
Loss of habitats for animals may lead to extinction.
Lesson 3: Case study - The California wildfires of October 2007
Learning objectives:
To develop a case study of the California wildfires of October 2007 including the main causes and effects of the fires.
To consider whether the California wildfires of October 2007 were predominantly a natural or a human hazard.
The October 2007 California wildfires were a series of wildfires that began burning across Southern California on October 20. They covered the area from Santa Barbara County to the U.S.–Mexico border (almost 400km in length). The raging fires were visible from space. The last fire was fully contained on November 9, 2007, 19 days after the series of fires started.
The two largest fires were in the San Diego area where 640,000 poeple had to evacuate their homes.
Effects
The fires forced approximately 1,000,000 people to evacuate their homes, the largest evacuation in California's history.
Over 1800 homes were destroyed.
Over 2,000 km² of land burned.
Nine people died as a direct result of the fires. 85 others were injured, including at least 61 firefighters.
Damage to property estimated at US$1.6 billion.
Air pollution levels raised across the area to 3 times their normal level - this causes breathing difficulties. People were advised to stay indoors.
Tourist trade was damaged. San Diego Zoo and Sea World were closed.
Drinking water in some cities was pollutd and people were advised to drink only bottled water.
Crops were destroyed, either by the fire itself or because they weren't watered as the farm workers had been evacuated. Food prices rose.
Many species of plants and animals were killed.
The table below shows some of the effects on San Diego County
Fire name | Date / time started | Area burned | Structures destroyed | Injuries | Containment |
---|
Witch (Creek) |
October 21 at 11:00 a.m. |
197,990 acres (801 km2) |
1040 homes 414 outbuildings 239 vehicles 70 homes damaged 25 outbuildings damaged |
2 deaths 39 firefighters 2 civilians |
100% |
Harris |
October 21 at 9:30 a.m. |
90,440 acres (366 km2) |
206 homes 252 outbuildings 253 structures damaged
|
5 deaths 34 firefighters 21 civilians |
100% |
Poomacha (Palomar Mountain/Valley Center) |
October 23 at 3:13 a.m. |
50,176 acres (203.06 km2) |
143 homes 77 outbuildings |
21 firefighters |
100% |
Horno/Ammo |
October 24 |
21,084 acres (85.32 km2) |
|
6 firefighters |
100% |
Rice |
October 22 at 4:16 a.m. |
9,000 acres (36.4 km2) |
206 homes 2 commercial properties 40 outbuildings |
5 firefighters |
100% |
McCoy |
October 21 |
300 acres (1.21 km2) |
1 residence 1 outbuilding |
|
100% |
Coronado Hills |
October 22 at 1:50 a.m. |
250 acres (1.01 km2) |
2 outbuildings |
|
100% on Oct. 22 |
Wilcox |
October 23 |
100 acres (0.40 km2) |
|
|
100% |
Responses
Over 6,000 firefighters worked to fight the blazes; they were helped by units of the United States Armed Forces,United States National Guard, almost 3,000 prisoners convicted of non-violent crimes, and 60 firefighters from the Mexican cities of Tijuana and Tecate.
California Governor Arnold Schwarzenegger declared a state of emergency in seven California counties where fires were burning.
President George W. Bush agreed, and ordered federal aid to supplement state and local response efforts.
Natural causes
Major contributing factors to the extreme fire conditions were drought in Southern California, hot weather, and the strong Santa Ana winds with gusts reaching 85 mph (140 km/h).
The fires occurred at the end of a dry summer and were exacerbated by the seasonal Santa Ana winds.
Southern California was in the midst of an unusual drought; in Los Angeles it was the driest year on record. The combination of wind, heat, and dryness turned the chaparral into fire fuel. Officials believed that some of the fires generated their own winds.
Human causes
Increasing number of homes built in canyons and on hillsides surrounded by brush and forest.
Several were triggered by power lines damaged by the high winds.
One fire started when a semi-truck overturned.
Another was suspected as having been deliberately caused; the suspect was shot and killed in flight by state authorities.
A 10-year-old boy admitted that he accidentally started the Buckweed Fire playing with matches.
Causes of the remaining fires remain under investigation.
Useful links:
BBC News article from 23rd October 2007 including a useful map
Excellent animations from the GIS Force Group showing the spread of the San Diego fires and the direction of the winds
Lesson 4: Reducing the damaging effects of wildfires
Learning objectives:
To be able to describe the strategies and methods used to reduce the damaging effects of wildfires including evacuation, education and the role of the emergency services.
What links these images?
Google have hired a herd of 200 goats to help them reduce the risk of wildfires at their headquarters! The goats graze on the land around the building, chomping their way through vegetation which might otherwise act as a fuel for wildfires. (I'm not kidding!). You can learn more about the Google Goats by clicking on the link at the bottom of this lesson.
This is just one of a variety of ways in which people can reduce the damaging effects of wildfires. The strategies and methods that people use fall into two main categories:
(a) preventing the wildfires from happening in the first place, and
(b) stopping the fires from spreading and causing damage once they are alight.
Preventing the wildfires from happening in the first place
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