How wildfire impacts on our water

Mar 29, 2022 | Activities

Once a wildfire is extinguished, you may think that it’s the end of the fire. But the impact on biodiversity and ecosystem services will continue to play out for a long time to come. 

Fire, for example has the potential to alter the dynamics of stream ecosystems and degrade the water quality. High intensity fires – or fires that burn with extreme heat – can cause enormous damage to water catchments. They destroy the ground cover and change hydrology, and they alter the structure, behaviour and erosion of soil.

The biggest impacts are seen if there is heavy rain soon after a fire. The loss of vegetation and altered soil structure can make fire-affected soil more prone to erosion. Runoff can carry sediment and pollutants into our water sources, affecting drinking water quality and agricultural industries. When vegetation is burnt, it can bring about change in the storage and processes of the hydrological cycle.

When riparian vegetation is lost, it could lead to sediment or soil (measured as turbidity) entering water sources and could also increase stream temperatures due to a lack of shade.

Chemical reactions triggered by fire can release nutrients, metals and other toxicants stored in vegetation and soil. And when it rains after a fire, it can wash these contaminants into waterways and reservoirs, which can have a substantial impact on agriculture and even on human safety.

The degree to which water quality is affected by fire depends on factors such as:

  • Geographical features and size of the catchment area.
  • Size and extent of the fire.
  • The time period between the last fire and a significant rainfall event.
  • Type of surrounding vegetation, soil and erosion.

The local food chain can also be affected which leads to:

    • Higher water temperatures
    • Increased light availability
    • Loss of habitat
    • Reduced protection from predators for instream biota.

What can be done to minimise impact on water quality following a fire?

    • Installing erosion and sediment control measures can prevent debris being washed into waterway
    • Control measures can include silt fences, hay bales and planting vegetation to stabilise soil.
    • Restoring burnt riverbank vegetation must be prioritized.
    • Establishing a water quality monitoring programme can help to monitor the quality of the water following a fire.
    • Aquatic ecosystems are remarkably resilient and often recover quickly if there is connectivity between affected and unaffected habitats.

Why our area is important…

The Kogelberg Biosphere is classified as a strategic water source area. It provides good quality water not only to the inhabitants of the Biosphere, but also for the Cape Metropolitan Area.

That makes it vital to minimise wildfires, focus rather on ecological burns and remove invasive alien plants – which remain one of the biggest fire threats in our area.


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