Monthly Water Report
Monthly Water Report
The Monthly Water Report provides a summary of the status of Victoria's water resources and water supplies at the end of the reporting month. It is based on validated water resource information provided by Victoria's 19 Urban and Rural Water Corporations and the Bureau of Meteorology. Each month's report is published online the following month. For detailed, specific and up-to-date information, please contact the relevant Water Corporation or the Bureau of Meteorology. Links to these organisations are located within the Monthly Water Report.
In April, rainfall was below average across most of Victoria. Gippsland, the North East, the Wimmera-Mallee and the Otway Coast received below average rainfall. Parts of the North East and Central Highlands received very much below average rainfall, as did isolated areas in Gippsland and the Mallee. Rainfall was classed as average along the Lower Murray from the north west as far east as Yarrawonga, and through the North Central region down to Melbourne. The inland south west and part of Central Gippsland also had average rainfall. The wettest station in the state was Mt Sabine, where a total of 126.8 mm of rainfall was recorded during April. The driest stations were Hopetoun Airport and Woomelang, each with only 0.8 mm of rainfall during the month. Statewide, the rainfall total was 62% below average
Streamflow rates in April remained very low in the west of Victoria, continuing the dry trend that has persisted throughout 2015 and into 2016. A small area on the south west coast was an exception to this. Streamflow was low to moderate throughout Gippsland, with the lowest streamflow around Central Gippsland. The highest flows in the state were recorded at the Merri River at Woodford, at 62% of the long term average. The Snowy River downstream of Basin Creek and the Yarra at Mulgrove recorded flows at between 40 and 59% of the long term average. All other stations experienced less than 39% of the long term average.
At the end of April, flows at 17 of the 28 representative stations were less than 10% of the long term average for the month, with no flows (i.e. the rivers were dry) at 12 of these stations. Of the 16 representative stations which were flowing, all recorded higher flows than the April historic minimum.
The total volume of water held in Victoria's major storages decreased by 3.0% during April, ending the month at 34.8% of capacity. Storage volumes fell in all of the 16 monitored basins. The smallest fall of 0.2% was in the Ballarat system, while the Thomson Macalister storages fell by 11.6%.
Victoria's regional storages decreased by 3.2% to 30.6% of capacity during April 2016. Melbourne's storage levels decreased by 2.1% to 59.9% of capacity over the same period. Melbourne's storages are 9.7% lower and the regional storages are 20.2% lower than at the same time last year.
Restrictions on urban water supplies
Urban water restrictions that were applied during March by Barwon Water, South Gippsland Water and Grampians Wimmera Mallee Water remained in place during April. At the end of April, 22 towns were on restrictions, the same as at the end of March.
The groundwater section of the Monthly Water Report is updated on a quarterly basis. For the last update go to the March 2016 report.
During April, 1% was allocated to high-reliability water shares in the Campaspe system and 2% in the Loddon system. A 5% allocation was made to low-reliability water shares in the Macalister Irrigation District. All other systems remained the same.
Restrictions on diversions from unregulated streams
At the end of April 2016, there were 150 unregulated streams and lakes subject to diversion restrictions, compared to 157 at the end of March. This time last year, there were 97 waterways subject to restrictions.
Seasonal climate outlook
BoM released its May to July 2016 rainfall outlook on 28 April 2016. The outlook has changed, and suggests that northern Victoria is the most likely to have above median rainfall over May through to July, with a 55-75% chance. The southern Wimmera, central regions and South Gippsland are predicted to have a roughly equal chance of exceeding median rainfall, while the south west coast has a lower chance, 40-45%. Above average May to July rainfall forecast for parts of Victoria is welcome, particularly in areas suffering from mid to long-term rainfall deficiencies, however recovery is likely to require a significant period of above average rainfall. The next update is expected on 26 May 2016.
The Bureau of Meteorology (BoM) released its latest ENSO Wrap-Up on 26 April 2016. The 2015–16 El Niño is in its last stages. Climate models now suggest the likelihood of a La Niña forming in the second half of 2016 is around 50% and the ENSO outlook is now at La Niña watch. The tropical Pacific Ocean sea surface temperatures cooled significantly over the second half of April and are approaching neutral levels. However, the atmosphere is not responding immediately to these changes so the Southern Oscillation Index (SOI) and cloudiness near the Date Line continue to fluctuate around El Niño levels.
Climate models suggest that the tropical Pacific Ocean will return to neutral levels within the next month. By September, the models suggest that La Niña thresholds are likely, although individual models show a spread between neutral and La Niña. La Niña is often, but not always, associated with above-average winter-spring rainfall over northern, central and eastern Australia. Australia's climate is also being influenced by record warm temperatures in the Indian Ocean. The warmth in the Indian Ocean may provide extra moisture for rain systems as they cross Australia during the southern autumn. The next ENSO update is expected on 10 May 2016.