How Do Wildfires Impact Water Resources?

Over the last few years, wildfire season around the world has really come to the fore as a topic for significant concern, with many regions around the world – including Australia, North America and Europe – experiencing the worst blazes in a decade.

As climate change intensifies and global temperatures continue to soar, the risk of these fires breaking out will also increase… and even the UK, with its famously damp climate and wet weather, is expected to see a rise in more intense and extreme wildfires in the relatively near future.

Last year, a study carried out by the University of Reading predicted that the danger of wildfires in the UK would increase in the future, with parts of eastern and southern England facing the highest risk levels on almost four days a year on average by 2080, compared to once every 50-100 years currently.

As temperatures rise and summer rainfall drops, conditions highly conducive to these fires could be almost five times more common in some regions as we near the end of the century. And, in the driest places, habitats could consequently be at risk for up to four months per year, on average.

Climate scientist professor Nigel Arnell said at the time: “Extremely hot and dry conditions that are perfect for large wildfires are currently rare in the UK, but climate change will make them more and more common. In future decades, wildfires could pose as much of a threat to the UK as they currently do in the south of France or parts of Australia.”

And now Scottish Water has issued calls to raise awareness of wildfire risks to help prevent damage and protect both the natural environment and water supplies, with at least 12 wildfires seen in the last five years on land covering thousands of hectares in different parts of the country, including the Isle of Skye and South Ayrshire.

David Anderson, catchment liaison officer with Scottish Water’s land management team, said: “We are seeing a dramatic increase in wildfires with the traditional wetter areas experiencing longer, drier periods than normal. And we are seeing wildfires in areas not normally associated with wildfires.

“Fires have the potential of setting peat on fire which can burn for long periods of time, possibly for a week or more. If this happens, it can destroy the carbon capture properties of a healthy bog or moorland.

“Soils are one of the biggest carbon reservoirs on earth, storing more of this element than the atmosphere and the above-ground biomass put together. Usually grass, heath and heather would grow back but there are areas where peat can burn and soils are lost.

“So wildfires are something that people in all parts of the country need to try to prevent and we need everyone, young or old, to help do their bit to protect the environment, including wildlife and drinking water sources.”

Wildfires can cause serious damage to the natural environment, ecology and wildlife, affecting the likes of insects, frogs, voles and nesting birds, as well as bruning trees and peatland, which are valuable carbon stores and which, when burnt, release greenhouse gases into the atmosphere and prevent them from capturing more carbon in the future.

In addition, ash from wildfires and the destabilisation of these peatlands near waterways can cause issues with water sources such as reservoirs which, in turn, leads to changes in raw quality. In Scotland, approximately 70 per cent of the public drinking water supply has its source in around 525,000 hectares of peatland and moorland.

How wildfires affect water quality

One of the big impacts of extensive wildfires is the production of wildfire ash from burned slopes, which is full of nutrients and other contaminants. These then make their way into rivers, lakes, streams and reservoirs, contaminating the drinking water supply and affecting aquatic ecosystems.

While these fires can destroy land-based ecosystems in just a few days, the lasting effects for dissolved organic matter (DOM) in terms of quantity and composition can remain for decades – and this, in turn, can cause issues where water treatment is concerned.

As this article in the EOS journal explains, while DOM is not a contaminant that can affect human health directly, it can cause off colourations and change the taste of water, as well as serving as a substrate for undesirable microbial growth.

It can also drive up treatment costs and chemical demand levels for the likes of chlorine and ferric iron, which are necessary to disinfect supplies and remove DOM.

Recent research now shows that the degree of water quality impairment markedly increases in line with wildfire severity. As wildfires burn more intensely and consume more fuel, water quality is expected to progressively degrade.

How can the impact of wildfires be mitigated?

A new partnership between Australian water supplier Water New South Wales, United Utilities, the Island Council of Tenerife and a team from the University of Swansea have now developed a set of tools and an end-user model that can predict the transport of contaminants, ash and sediment following actual or anticipated wildfires in the future.

This new model also includes the identification of erosion hotspots in water catchments that can be treated to prevent erosion and contamination events altogether.

In addition, a new erosion mitigation treatment has also been developed for reducing soil and ash movement, a treatment that is already being applied in the Canary Islands as standard practice, thanks to its superior efficacy and cost effectiveness, in comparison to traditional emergency hillslope treatments.

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