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
Last updated:
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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 cool season in WA’s South West Land Division
  • respond to 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 previous decades, we need more rainfall now to recharge water resources to 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 South West Land Division that are representative and of particular interest: Denmark, Gingin Brook, Harvey River and Pemberton. 

If you would like graphs or data for other locations, please contact us or use the links below.

Denmark – rainfall and streamflow tracking

Rainfall

The Denmark site is tracking to receive 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.

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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 average streamflow for the January to December period. 

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

  • at most, average
  • or, at the lowest, below 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.

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If the amount of rain differs from the current forecast, the range of rainfall at Gingin Brook across January to December is tracking to be:

  • at most, average
  • at least, below 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). 

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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.

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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 spring, given the Bureau of Meteorology’s forecast and what has happened so far this year (including summer’s dry conditions).

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

  • at most, average
  • at least, 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. 

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

  • at most, average
  • at least, below average

Streamflow

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

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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

The Bureau of Meteorology expects wetter than average rainfall for most of the South West Land Division for October to December. The Indian Ocean Dipole and the El Niño Southern Oscillation are currently neutral. If a La Nina develops in the coming months it is likely to be weak and short-lived.  

South West rainfall – September 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. 
9-southwest

Almost 95% per cent of sites recorded below average or lower rainfall totals for September. Two sites (Kondinin and Newdegate) had average monthly totals.

10-southwest

* 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 – September and 2024 overview

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

  • Gardner River is the one location that has recorded above average streamflow for 2024 so far.
  • Gingin Brook has had lowest-on-record streamflow for the year to date.  
11-southwest

September streamflow across the South West Land Division ranged from average to well-below average:

  • About half the sites had average September streamflow totals and the other half below average totals.
  • Gingin Brook had well-below average flow in September. 
12-southwest

† 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 – its driest autumn since 20193
  • winter rainfall has been average for much of the South West Land Division.

Rainfall decline in the South West has been larger 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 to October rainfall​1
  • about 80 per cent less flow into Perth’s water supply dams2
  • less recharge to groundwater.  

Climate change poses significant challenges for communities in Western Australia (WA) who are experiencing more extreme weather events such as tropical storms, floods and bushfires. The State Government is supporting businesses, communities and local governments to understand the future climate and adapt to the impacts of climate change.

The Climate Science Initiative (CSI) will produce the most detailed and comprehensive Western Australian climate change projections to date, extending to the year 2100. For more information visit: Climate Science Initiative.

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 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 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 do 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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