Department tracking rainfall and streamflow for 2020

Department tracking rainfall

and streamflow for 2020

New data from the Department of Water and Environmental Regulation (DWER) has shown a late start to streamflow at many sites following good May rainfall across most of the South West land division.

Despite the average to above average rainfall, streamflow was below average for most sites during May and also for the year to date. This follows on from dry conditions experienced across the South West of the state in 2019.

Streamflow data for May showed that 58 per cent of sites recorded well below average flow and 21 per cent below average flow, with only the sites at Wilyabrup Brook, Margaret River and Lort River recording average streamflow for May and the year to date.

The Denmark River gauging station recorded its first flow at the start of June. This is the first time the site has recorded no streamflow in the first five months of the year since records began. Sites on the Swan River and Thomson Brook also recorded no streamflow until the start of June, and the Frankland River gauge recorded its lowest reading for January to May since 1975.

In total five sites recorded their lowest January to May streamflow totals and only Margaret River, Wilyabrup Brook and Lort River recorded average streamflow for the period.

DWER tracks rainfall at 36 sites and streamflow at 19 sites across the South West of the state and the data for May shows average to above average rainfall at 34 of the sites (56 per cent recorded average levels and 39 per cent recorded above average levels).

For the year to date (January to May) two thirds of the sites recorded average rainfall with the Kent River and

DWER measurement at Roe Highway on the Helena River.

Cowaramup sites recording well above average, five sites (including Denmark and Pemberton) recording above average rainfall and a further five sites (including Esperance, Gingin Brook and Geraldton) recording below average rainfall.

Looking ahead to the likely rainfalls for the winter, using combined data from the Department of Primary Industries and Regional Development (DPIRD) and the Bureau of Meteorology (BoM) for June to August, the outlook indicates below average to above average winter rainfall over the South West of the state, with a higher probability of below average rainfall for the northerly and easterly areas.

For the majority of the South West the latest BoM outlook indicates a 45-65 per cent chance of exceeding median rainfall for August to October.

Streamflow forecasts indicate streamflow for June to August has a greater tendency to be below average throughout the South West of the state.

The impact of climate change on water supplies is a significant issue for the state’s South West region, one of the most-affected places in the world in terms of reduced rainfall.

Measuring rainfall and streamflow is essential for DWER to be able to assess and advise on how to best manage the region’s water resources.

Mt Frankland Rock Bar stream

Looking at the city of Perth, from January 1 to June 30 the rainfall measurement at the Perth Airport gauge shows 271mm, slightly lower than the average Jan-June rainfalls since 1975 of 300mm.

Recharge to the Gnangara groundwater system started in April, with water level rises recorded across the superficial aquifer for the month of May.

For more information on how the department manages Western Australia’s water resources visit https://www.dwer.wa.gov.au/water.