Article
BAMOS October 2021
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Figure 1 ( top ): Murrumbidgee river height at Wagga Wagga ( April to September ) 1885 – 2019 . The first recorded April height position on the bottom axis , every 5 years , is indicated . The minor flood level is marked ( dashed black line ) at 7.3 m . Note that since 1991 , in these months only one minor flood level was reached in 1995 and one major in 2016 .
Figure 2 ( bottom ): Murrumbidgee river heights ( m ) at the Hay town gauge and Hay Private Irrigation District gauge for each April to September 1874 – 2019 . There are concurrent readings at both locations from 1968 to 1982 ( Speer 2018 ). The first recorded April height , every 5 years , is indicated . The river flood level is marked by a dashed black line at 6.7 m . Of the six months April – September , the most recent maximum weekly river height value for each individual month exceeding the flood level of 6.7 m is indicated . Note that since 1991 there have been no April – September flood height exceedance peaks and the most recent June flood height exceedance was 5 June 1956 .
strengthening and extension of the subtropical high pressure ridge during winter which shifts rain-bearing weather systems southward ( Murphy and Timbal , 2008 ; Peterson et al . 2021 ). Specifically , the lack of negative-phase
Indian Ocean Dipole ( IOD ) events is identified as a contributing factor to the drying and resulting droughts in southeast Australia since the 1990s ( Ummenhofer et al . 2009 ), where the influence of the IOD is greatest in June – October ( Risbey et al . 2009 ). Other important climate drivers of cool season precipitation identified in this study are the atmospheric-based
southern annular mode ( SAM ), which in its positive phase is also a major influence on the drying trend by its association with rain-bearing systems shifting southward away from southern Australia ( Bureau of Meteorology 2019 ; Post et al . 2014 ); the basin-wide Pacific Ocean phenomenon , the inter-decadal Pacific oscillation ( IPO ); and global sea-surface temperature . Machine learning attribute detection of the main climate drivers that influence precipitation in the Murrumbidgee River catchment is described in the new research .
The Millennium Drought ( 1997 – 2009 ) and the extremely dry years 2017 – 2019 characterise recent decades in southeast Australia . There have been other droughts and the historical Federation Drought ( 1895 – 1903 ) most notably is one of those . However , in early December 2006 , the Australian newspaper reported that inflows to the nearby River Murray system between June and November were 610 gigalitres , ‘ just 56 percent of the previously recorded low in 1902 ,’ when the Federation Drought was at its worst ( Guest 2016 ). In addition , there are extreme variations in the volume of water reaching the Murray Mouth from the MDB due to frequent severe droughts with the lowest ever recorded being 6,740 gigalitres also in 2006 ( Guest 2016 ).