In the future of wildfire detection, who are the guardians of the forest?
You cannot outrun a forest fire. Wildfires can spread shockingly fast ─ up to 23km/h (14mph) under the right conditions ─ consuming everything in their path. When they take hold, they are often extremely destructive, highlighting the vital need for early wildfire detection.
Wildfires are a huge and growing problem. They cause around 20% of global CO2 emissions, almost the same as all traffic worldwide. Burning forests not only decimate the world’s largest carbon capture and storage system but also eliminate the habitat for two thirds of all biodiversity on earth.
In addition to their environmental impact, wildfires also cause huge economic damage.
By detecting wildfires while they are still small, we stand a much better chance of stopping them before they cause too much damage, saving money, the environment and, ultimately, lives.
So, how do we detect wildfires?
Traditionally, there have been three main ways we detect wildfires: watchtowers, cameras and satellites. A novel fourth approach involves the use of gas sensors. This technology has recently been developed and is now being added to the mix, helping to fill in some of the gaps left by the other three.
In this article, we will explore the pros and cons of each approach, considering the best combination for wildfire detection.
Wildfire Detection from Watchtowers
The classic approach to wildfire detection involves placing manned watchtowers in and around a forest, with individuals checking for smoke. By setting up multiple watchtowers, it becomes possible to triangulate and dispatch firefighters to the exact location of the fire. Fire watchers can then use the towers to keep track of the size and location of the fire as it progresses.
We have used this approach for a long time and it has proven pretty reliable. Modern technology is now taking over this role, utilizing cameras mounted on the towers, often equipped with Artificial Intelligence (AI) to detect smoke and automatically signal the fire service.
Advantages
Watchtowers, whether manned by humans, cameras or AI, have the advantage of being able to overlook a large area. A single watchtower on a clear day has an observable radius of up to 18km. This means that relatively few of them are needed to keep watch over a large forested area.
Disadvantages
The main problem with using watchtowers for wildfire detection is that the smoke has to rise above the tree canopy to become visible, which means the fire is already quite large. Tree canopies act like a blanket, holding down the smoke. It’s only when the fire is large enough that it creates an updraft strong enough to push the smoke above the tree canopy.
As such, it is basically impossible to detect a small fire underneath the tree canopy, which is where the vast majority of wildfires start. By the time they are large enough to be seen, they will have been burning for hours and may be too large to extinguish by the time the firefighters arrive at the scene.
The other main issue with watchtowers is visibility. Haze, fog or dust from crop harvesting can obscure visibility or cause false-positives, and of course there are often obstacles such as hills which can block the view. It can also be very difficult to see smoke at dusk or dawn, further reducing the reliability of watchtowers.
Detecting Wildfires with Satellites
A space-age solution to wildfire detection is using satellites. Observational satellites can have geostationary orbits, where the satellite is in a fixed location relative to Earth, or Low Earth Orbits (LEO), where the satellite moves relative to the Earth.
Each type of satellite uses camera technology to keep a lookout for wildfires. Geostationary satellites will keep watch over one area of forest while a LEO satellite will work as part of a network to provide global coverage.
Advantages
The key advantage of using satellites is the sheer size of the area they can observe. A single geostationary satellite can provide coverage of around a quarter of the entire surface of the Earth.
Given their wide field of view, satellites are fantastic at tracking the progression of wildfires. They can take weather patterns and terrain into account, helping firefighters predict the route a wildfire will move and assisting with evacuating areas most at risk.
Disadvantages
Both geostationary and LEO satellites have their drawbacks.
Geostationary satellites orbit the Earth at distances of around 35,888km. At this distance, a single pixel is the equivalent of 500x500m. This means that the fire already needs to be very large before the satellite can detect it.
LEO satellites are much closer to the ground ─ around 600km above the Earth’s surface ─ so can provide substantially better resolution. Unfortunately, since they are constantly on the move relative to the Earth’s surface, they only pass each area once every six hours at most. In six hours, a fire could have progressed from the smouldering stage to become very large and, potentially, unstoppable.
As such, satellites are not ideal when it comes to early detection of wildfires, but are much more suitable for monitoring them, predicting where and how they will develop and assisting firefighting and evacuation efforts after a wildfire has already grown out of control.
Detecting Wildfires using Gas Sensors
Gas sensors are a relatively new technological approach to wildfire detection, functioning like digital noses that can ‘smell’ a fire. They are positioned in forests below the tree canopy and use AI to accurately detect smoke from fires.
These gas sensors are typically solar-powered, allowing them to be positioned anywhere and run for more than 10 years without the need for an external power supply or battery swap.
Advantages
The main advantage of gas sensors is that they can detect wildfires as early as the smouldering stage. Since the fires are very small at this stage, they can be extinguished much more easily and effectively before they spread and cause real damage.
The other advantage of gas sensors is their cost. At less than $100 per sensor, they are the cheapest of the three detection methods. Cameras cost around $120,000 to build while satellites cost around $1.3 million to build and launch. While it’s true that a large number of sensors are required to create a network within a forest, the overall protection cost is still very competitive when compared to other approaches.
Disadvantages
The disadvantage of gas sensors is their limited range in comparison to, say, satellites. One sensor is needed for each five hectares of woodland (more in high-risk areas)
Gas sensors are, therefore, best suited to cover high-risk, high-value areas in the wildland urban interface (WUI) ─ places where people hike, camp or drive, power lines and railroad tracks, as well as anywhere else where fires have proven more common.
Combining detection methods for an ideal solution
So, there are advantages but also limitations to every wildfire detection approach. There is no silver bullet that will solve the growing wildfire crisis on its own. However, by combining multiple solutions, it is possible to create an optimal system. The advantages of one approach can be used to cancel out the disadvantages of another.
Since most wildfires are caused by human activity, it makes sense to focus gas sensors on wildland-urban interface (WUI) areas ─ the areas of forest that come into most contact with people ─ which are the highest risk. Since these areas are relatively small, they can be effectively covered by gas sensors for ultra-early detection at a low cost. Despite currently being relatively small in area, they are increasing by around two million acres a year, and they are the very area where wildfires can wreak the most damage, owing to their proximity to humans and human infrastructure. This makes ultra-early detection especially important in an area where sensor-based approaches are far superior.
Outside human activity, the only natural causes of wildfires are lightning, lava, and (very occasionally) meteors. Lava is uncommon and relatively easy to predict yet almost impossible to stop anyway. Lightning is less predictable yet highly visible, making it easy to spot with cameras mounted on watchtowers. Wildfires caused by meteors are extremely rare but tend to be very visible so are often easier to spot and tackle.
If a wildfire does develop outside of the high-risk areas or out of view of the cameras, it can then be detected and tracked using satellites, helping to reduce the damage and loss of life.
By combining all three approaches, we could effectively manage the majority of wildfires before they become too large and unmanageable. Not only would this save forests but it would also save homes, livelihoods and lives, both of the public and of firefighters tackling the blaze.
With wildfires becoming more common, more intense and more deadly, it is more important than ever to invest in wildfire detection. Finding the perfect mix of approaches is going to be a far better solution than picking a favourite, and it could help enable the future development of automated firefighting systems.
Sources:
https://wfca.com/articles/how-fast-do-wildfires-spread
https://www.iii.org/fact-statistic/facts-statistics-wildfires
https://hrcak.srce.hr/file/353960
https://www.dryad.net/wildfiresensor
