Heavy rain and flooding across parts of Australia

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  • Many roads in Australia have been cut off as a result of flooding. Photo: Andrew Milligan/PA Wire.

    MODIS image of flooding along the border of Queensland and New South Wales on 6th February 2012. Photo: NASA.

    MODIS image of flooding along the border of Queensland and New South Wales on 18th February 2012. Photo: NASA.

    Figure 4: Expected rainfall for the 72 hours from 00UTC 03/03/2012 as predicted by ECMWF. Note the white areas where rainfall exceeds 50 mm.

  • Heavy rain and flooding across parts of Australia
    03.03.2012 15:48

     

    Spells of heavy rain across parts of Australia this week has led to severe flooding and the evacuation of thousands homes in the Northern Territory, New South Wales and Victoria. The rains have coincided with ‘La Nina’ in the Pacific Ocean, an intriguing phenomenon that brings wetter-than-average conditions to much of Australia and western Pacific Islands

    Australia, positioned in the south-western corner of the Pacific Basin is heavily influenced by the coupled oceanic-atmospheric effect known as the El Nino Southern Oscillation (ENSO). This is characterised by the relationship between the temperature of the sea surface and the air pressure aloft. Every few years or so the sea surface temperatures across the western Equatorial Pacific oscillate between below average ('El Nino') and above average ('La Nina') states. The current ENSO mode is 'La Nina', and what this means for Australia is an increased incidence of rainfall, particularly in eastern areas. In simplified terms, the warmth of the water in a ‘La Nina’ enhances rainfall due to greater moisture availability.

    Although the 2011/2012 La Nina event is in decline, the past few months have still seen a series of heavy rainfall events, with this week in particular being a significant example. A swathe of locations have recorded daily rainfall totals in excess of 100 mm, figures that can devastate property by swelling rivers and causing excess runoff.

    Examples of rainfall this week include 104.1 mm at Albury, New South Wales on Tuesday after an active trough had passed through. A staggering 210.2 mm was recorded in 72 hours up to Friday morning at Merimbula, located on the Sapphire Coast of New South Wales. To put this into perspective, mean February rainfall for Albury and Merimbula are 52.1 mm and 76.0 mm respectively.

    Although a welcome relief for farmers who were hit last year by bush fires, the rainfall has forced thousands of people to evacuate their homes as rivers have reached critical levels. Many more have been told to prepare to leave their properties, mostly in New South Wales where this weekend will see the worst of the continued deluge. According to the New South Wales state emergency service, around 75% of the district is under a serious flood watch.

    Furthermore, a large dam in Canberra, built in 1912 after a severe drought, is fully submerged for the first time in its history and is likely to overflow. Meanwhile, the Warragamba dam near Sydney has already started overflowing threatening 900 homes. The forecast for the next few days is for heavy rain to continue in many eastern areas, as shown by Figure 4.

    By: Nick Prebble