How the South West is tracking for rainfall and streamflow this season

Information to help water users based on how wet we expect the South West to be in 2024
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Up-to-date rainfall and streamflow information is vital to plan and adapt operations that rely on water. 

The Department of Water and Environmental Regulation helps the community and State Government to:

  • track rainfall and streamflow over the season in WA’s South West Land Division (SWLD)
  • respond to yearly changes in rainfall and streamflow
  • investigate the rainfall and streamflow ranges that may occur
  • collectively prepare for potential dry periods or other rainfall impacts 
  • coordinate any required response to manage industry, agriculture and drinking water supplies.

Compared with decades ago more rainfall is needed now to recharge water resources to those historical levels because climate change is altering the way our water systems respond to rainfall. However, intense events can still cause localised flooding.

The tracking information below is for four key sites across the SWLD that are representative and currently of particular interest: Denmark, Gingin Brook, Harvey River and Pemberton. Department staff can access tracking graphs for additional sites and others can use the links below to find relevant data for other locations.

Denmark – rainfall and streamflow tracking

Rainfall

The Denmark site is tracking to receive well below average rainfall for January to December, given the below average amount of rain so far this year and the Bureau of Meteorology’s forecast. 

If the amount of rain differs from the current forecast, Denmark’s rainfall across January to December is tracking to be:

  • at most, below average
  • at the lowest end of the range, well below average.  

Streamflow 

The amount of water flowing at the Denmark River site is currently tracking at below average. Given the Bureau of Meteorology’s forecast Denmark is tracking to receive below average streamflow for the January to December period. 

If the amount of streamflow differs from the current forecast, streamflow at Denmark across January to December is tracking to be:

  • at most, average.  

We will continue to monitor Denmark River flows. 
 

Gingin Brook – rainfall and streamflow tracking

Rainfall

The Gingin Brook site is tracking to receive average rainfall for January to December, given the average amount of rain so far this year and the Bureau of Meteorology’s forecast. 

If the amount of rain differs from the current forecast, the range of rainfall at Gingin Brook across January to December is tracking to remain as average. 

Streamflow

The amount of water flowing at the Gingin Brook site is tracking to be well below average, given the Bureau of Meteorology’s forecast and what has happened so far this year (including summer’s dry conditions). 

If the amount of streamflow differs from the current forecast, Gingin Brook streamflow across January to December is tracking to be:

  • at most, well below average
  • or, if the lowest amount of monthly streamflow since 1975 happens again, a record low. 

We will continue to monitor Gingin Brook flows. 

Harvey River – rainfall and streamflow tracking

Rainfall

The Harvey River site is tracking to receive average rainfall for January to December, given the average amount of rain so far this year and the Bureau of Meteorology’s forecast. 

If the amount of rain differs from the current forecast, the range of rainfall at Harvey River across January to December is tracking to remain as average.

Streamflow

The amount of water flowing at the Harvey River site is tracking to be below average over summer, given the Bureau of Meteorology’s forecast and what has happened so far this year (including summer’s dry conditions).

If the amount of streamflow differs from the current forecast, Harvey River streamflow across January to December is tracking to remain as below average. 

We will continue to monitor Harvey River flows. 

Pemberton – rainfall and streamflow tracking

Rainfall

The Pemberton site is tracking to receive average rainfall for January to December, given the average amount of rain so far this year and the Bureau of Meteorology’s forecast.

If the amount of rain differs from the current forecast, Pemberton rainfall across January to December is tracking to remain as average. 

Streamflow

The amount of water flowing at the Lefroy Brook site is tracking to be below average over summer, given the Bureau of Meteorology’s forecast and what has happened so far this year (including summer’s dry conditions). 

If the amount of streamflow differs from the current forecast, Lefroy Brook streamflow across January to December is tracking to remain as below average. 

We will continue to monitor Lefroy Brook flows. 

Seasonal forecast

As at 7 November 2024, the Bureau of Meteorology expects:

  • a 45–65 per cent chance of exceeding median rainfall across the majority of the South West Land Division for December–February 
  • another very hot summer, with a 75–80 per cent chance of exceeding the median maximum temperatures for the South West Land Division in January–March. 
     

South West rainfall – November and 2024 overview

Long-term trends show declining rainfall in the South West (see ‘Climate context’ below).

Rainfall for 2024 so far has varied across the region: from above average to lowest on record. It has been:

  • above average at Geraldton, Roelands and Dalwallinu
  • average at about half of the department’s South West Land Division tracking sites
  • below or well-below average at around half of the sites
  • lowest on record at Kellerberrin and Kalgan River.
Rainfall deciles January to November for the SWLD

More than 70 per cent of sites recorded average or higher rainfall totals for November. Two sites (Dalwallinu and Roelands) had well above average monthly totals.

Rainfall deciles for November for the SWLD

* A rainfall decile is a way to compare the amount of rain for a particular place and period. The rain volumes at each location for the same calendar period for each year between 1975–2023 are ranked from least to most and then divided into ten groups. The first group (‘decile 1’) contains the lowest 10 per cent of rainfalls so it is the driest 10 per cent of measures and is considered to be a well-below average amount of rain. At the other end of the spectrum, ‘decile 10’ contains the highest/wettest 10 per cent of measures and is considered to be well-above average rainfall. The coloured circles in the map show how a 2024 rain amount fits with these 10 groups of ranked historical rainfall.

South West streamflow – November and 2024 overview

The varied rainfall conditions across the South West Land Division so far in 2024 has resulted in streamflows ranging from average to lowest-on-record for January to November 2024:

  • More than 50 per cent locations have recorded below average or lower streamflow for 2024 so far.
  • Gingin Brook has had lowest-on-record streamflow for the year to date. 
Streamflow deciles for January to November for the SWLD

November streamflow across the South West Land Division ranged from above average to lowest on record:

  • More than 80 per cent of the sites had below average or lower November streamflow totals.
  • Thomson Brook was the only location with above-average streamflow totals in November.
  • Gingin Brook had well below average flow in November and Kalgan River had its lowest on record.

 

Streamflow deciles for November for the SWLD

† A streamflow decile is a way to compare the amount of water flowing in a stream, river or other channel for a particular place and period. Streamflow at each location for the same calendar period for each year between 1975–2023 are ranked from least to most and then divided into ten groups. The first group (‘decile 1’) contains the lowest 10 per cent of streamflows and is considered to be well-below average streamflow. At the other end of the spectrum, ‘decile 10’ contains the highest 10 per cent of measures and is considered to be well-above average streamflow. The coloured circles in the map show how a 2024 streamflow fits with these 10 groups of ranked historical streamflows.

Climate context

The Bureau of Meteorology reports that:

  • autumn rainfall was below average for much of the South West Land Division, recording its driest autumn since 2019
  • winter rainfall has been average for much of the South West Land Division
  • rainfall totals in spring were below average in the southwest, even though several sites recorded their wettest spring day on record in late November.

Rainfall is declining in the South West more than anywhere else in Australia. Almost all climate projections indicate a warmer and drier future for the region, marking it as a global hotspot for reduced rain due to climate change.

Since the 1970s, in south-western WA there has been:

  • a 16 per cent decline in April–October rainfall​1​
  • about 80 per cent less flow into Perth’s water supply dams​2​
  • less recharge to groundwater. 
     

Useful links, water management responses, and bibliography

  • The Department of Primary Industries and Regional Development’s: 

Email surfacewater@dwer.wa.gov.au if you need more information.

Departmental water management responses

The department manages water proactively and reactively. We are:

  • delivering the Community Water Supplies Partnership program which boosts water infrastructure upgrades and improvements in 37 LGAs across the dryland agricultural area  
  • continually communicating with local government areas (LGAs) on the probability of water deficiency declarations in areas where on-farm water storage is at a median level or lower
  • assessing water resource conditions and reviewing allocation limits in priority areas  
  • implementing rural water and allocation planning, water licensing and climate adaptation programs to safeguard resources 
  • monitoring and managing key estuaries and rivers through the Healthy Estuaries WA and Healthy Rivers programs
  • further supporting rivers through the Creating Climate Resilient Rivers project which supports rivers to cope with short periods of extreme conditions, and to adapt and evolve to longer-term changes  
  • developing and delivering a research program addressing key climate challenges for the WA water sector.  

The State Government:

  • has invested $25 million in the Lower Great Southern Towns Water Supply Scheme. A response to years of declining rain, the project now ensures Denmark is no longer solely reliant on rainfall for its drinking water. To date, more than $4.3 million has been committed to 37 local governments for projects to alleviate demand on scheme water and increase the availability of non-potable water supplies 
  • will invest up to $15.3 million in key initiatives to improve water security for horticultural growers in the Manjimup–Pemberton region. 
     

Bibliography

Bureau of Meteorology: 

Essential information and disclaimer

The Bureau of Meteorology: 

  • issues weekly forecasts essential to the tracking information in this page; however, the department aims to update this webpage about monthly. The tracking information is relevant for the time of publication only; key information may have changed
  • forecasts use a slightly different time period to the department’s historical tracking time period.

The Government of Western Australia (State Government) is committed to quality service to its customers and makes every attempt to ensure accuracy, currency and reliability of the data contained in this page. This page is for information purposes only and the State Government cannot and does not represent or warrant that the document is free of errors, inaccuracies, faults or omissions. Changes in circumstances after time of distribution may impact the quality of this information. To the fullest extent permitted by law, the State Government and its officers and employees are released from liability (including in respect of negligence) for any loss, damage, cost and expense caused by use of or reliance on this document and the information contained on it. 

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