Jenny writes*
Temperatures in Australia have been rising by 0.5°C rise per decade since the 1980s due to climate change. In New South Wales (NSW), higher temperatures have intensified precipitation events and increased the intensity and frequency of droughts [Deb et al., 2020]. Intense precipitation increases fuel availability because it allows for widespread herbaceous plant growth in what would otherwise be barren land [Deb et al., 2020]. In combination with high temperatures, more fuel encourages bushfires, as occurred in 2019 in NSW, with negative consequences to water quality.
In the 2019/20 fire season, more than 3,200 km2 of native forests burned in the Lake Burragorang catchment, which supplies the Warragamba dam. Warragamba is Sydney’s largest dam (holding more than four times the water of Sydney Harbour when full); it provides about 80% of greater Sydney’s water. By mid-January 2020, reservoir levels had dropped to about 42% capacity. Only days after local fires were declared to be contained, the most intense rainfall in 30 years doubled the amount of water stored in Warragamba dam from pre-rainfall levels.
Thermal decomposition during bushfires creates ash and soil material high in nutrients (including nitrogen and phosphorus), metals and organics, which erode quickly due to lack of vegetative ground cover and surface litter. Heavy rainfall increases the rate of runoff of this ash and soil material to nearby water networks which can produce algal blooms that reduce water quality and dissolved oxygen, which leads to fish kills.
Bushfires in the Burragorang catchment can impact drinking water quality in Sydney. However, various measures prevented this in 2019/20. WaterNSW installed floating sediment booms across the Burragorang catchment to limit the movement of high turbidity water toward the Warragamba dam wall. Monitoring at sampling stations was increased and fallout radioactive nuclides were used to measure the transfer of sediments and nutrients from wildfire locations to downstream areas. However, in other areas like the nearby Tenterfield region, large quantities of ash entered the Tenterfield Dam, resulting in residents needing to boil water from October to December 2019.
Research suggests the “record high” temperatures of 2019 will be “average” by 2040 if emissions continue to grow [Sanderson and Fisher, 2020]. Additional actions that can minimise impacts of bushfires on waterways include hillside sediment erosion traps like silt fences and planting vegetation like grasses and trees to stabilise soils, and prioritising the restoration of burnt riverbank vegetation zones.
Bottom Line: Unprecedented weather events due to climate change are increasingly likely. It is imperative that water managers in Sydney adequately prepare and adapt to maintain high water quality as bushfires grow more frequent.
* Please help my Water Scarcity students by commenting on unclear analysis, alternative perspectives, better data sources, or maybe just saying something nice 🙂
Hey Jenny. Thanks for your post! You jam-packed a lot of information on the impacts of the climate crisis in Australia. I think you have good content here that you can integrate into your case study, I look forward to reading it in a few weeks.
I am interested to know if there are any existing papers that provide predictions on the Dam water levels for the coming 10 years. Of course climate change is causes unpredictable weather patterns that are difficult to pinpoint, but if you could find some reliable scientific research on your case watershed, it would really give a nice snapshot into the future water situation in Sydney. Will there even be a Dam left?
Anyways, I think you are on the right track to writing a successful paper. Keep up the good work!
Hey Sarah, thank you for your question and encouraging words!
It is difficult to say what rainfall and dam levels for the future might look like (we can only make assumptions and model!). One paper that I found used inflow, climate change and population forecasting to model the dam levels and see if it will continue to be able to supply Sydney’s population. They suggest that drought and heavy rainfall periods will persist in the next two decades, but water supply to Sydney from the dam will not be jeopardised (of course a lot of assumptions have been made to come to this conclusion!). WaterNSW state that when the dam is less than 75% full, water is transferred from other dams in the catchment.
If you are interested, have a look at this link that shows the dam levels from Feb 2017 to Jan 22. The dip coincides with the 19/20 bushfires and the subsequent large rainfall. As you can see, the dam levels have been at high capacity since Feb 2020.
https://waterinsights.waternsw.com.au/api/water-source/v2/updates/1570/attachment
Regarding your question of whether there will still be a reservoir with water in it behind the Warragamba dam in ten years, I think so. Whilst water shortages and drought are likely to continue being an issue in the future, in the last few months, high levels of rainfall have caused major flooding and a problem of too much water in the dam. In fact the level of the Warragamba dam today, Mar 15th 2022, is 100%! High rainfall has been seen in the late summer period for the past two years. Risk of flooding is so high that there has been a $1.6 billion project proposal for the wall of the dam to be raised by 14 m to temporarily store flood waters to reduce this risk. How to manage the fluctuations between long periods of drought followed by large rainfall is the key challenge for the dams in the Burragorang catchment.
Hi Jenny ! Thank you very much for your blogpost about fire and water (quality) in Sydney. I found it very interesting and I really enjoyed reading it.
You put a lot of information in your blogpost which is, in my opinion, really great and I liked the fact that you added a lot of quantitative data and wrote about very surprising/shocking facts like the one stipulating that “only days after local fires were declared to be contained, the most intense rainfall in 30 years doubled the amount of water stored in Warragamba dam from pre-rainfall levels”
Do you have any more information about the fact that the “record high” temperatures of 2019 will be “average” by 2040 if emissions continues to grow ? How come will it take around 20 years to get like this ? What can the authorities or/and the inhabitants of Sydney do in order to avoid the phenomenon ?
Like Sarah wrote it in her comment, I am convinced that you are going to write a very nice paper and I will be very interested in reading it !
Hi Flore, thank you for your message. I’m glad you enjoyed reading the post.
The abnormally high temperatures of 2019 may become normality by 2040 because of the effects of anthropogenic activities – large amounts of greenhouse gases are emitted into the atmosphere and global temperatures rise. The most effective course of action would be to immediately cut the emission of greenhouse gas (transitioning to renewable energies and low carbon circular economies and changing behaviours like eating less meat and dairy). Unfortunately, even if all emissions are cut today, temperatures will continue to rise because of past actions. Higher temperatures will increase the risk of bushfires. Authorities will need to work on fire mitigation and protection plans to ensure the safety of residents and the drinking water supply.
Also, if you are interested, you can look at this link where you can see a graph that shows the dam level change after the fires were contained at the beginning of 2020 which shows how intense the rainfall was. https://waterinsights.waternsw.com.au/api/water-source/v2/updates/1570/attachment
Well done!
Did the rapid inflow of water, one which is probably occurring once again given recent torrential rainfall, have any impact on water quality for urban use in Sydney?
Dear Dr.Pederson,
Good question! Because of the use of sediment booms and water treatment, there was no effect on water quality once it reached the customer. Following the bushfires / high inflows in 2020, March 2021 saw Sydney’s first major flood since 1990 with a peak of 12.9m. High rainfall from mid-Mar leading to significant catchment inflows to the dam resulted in it eventually spilling on 21th Mar (~1,200GL in total). Due to the 19/20 bushfires and 2020 inflows, the water quality in the dam was already low, with high levels of sediments and organic materials. However, thanks to extensive monitoring and filtration, there was no impact on the raw water supply and household water in Sydney. Let us hope that despite more heavy rainfall now in 2022, the monitoring and filtration by WaterNSW and Sydney Water will help to ensure that water quality remains high.