Special Climate Statement 66—An Abnormally Dry Period in Eastern Australia
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Special Climate Statement 66—an abnormally dry period in eastern Australia 1 November 2018 Special Climate Statement 66—an abnormally dry period in eastern Australia Version number/type Date of issue 1.0 1 November 2018 Unless otherwise noted, all images in this document are licensed under the Creative Commons Attribution Australia Licence. © Commonwealth of Australia 2018 Published by the Bureau of Meteorology Cover image: Farmland east of Bourke, 3 August 2018 (Photo: Mark Wilgar). 2 Special Climate Statement 66—an abnormally dry period in eastern Australia Table of contents Introduction .................................................................................................................................................................. 4 1. Rainfall deficiencies ........................................................................................................................................... 4 1.1. April 2012 to September 2018 (78 months) ...................................................................................... 4 1.2. January 2017 to September 2018 (21 months) ................................................................................. 5 1.3. July 2017 to September 2018 (15 months) ....................................................................................... 6 1.4. January to September 2018 (9 months) ............................................................................................ 6 1.5. Summary ........................................................................................................................................... 7 2. Other notable climatic features of 2018 ............................................................................................................ 8 2.1. Temperature and humidity................................................................................................................. 8 2.2. Soil moisture .................................................................................................................................... 10 2.3. Evaporation and wind ...................................................................................................................... 10 2.4. Fire danger ...................................................................................................................................... 10 3. Broadscale climate drivers influencing the current dry conditions .................................................................. 11 4. How has October 2018 rainfall affected deficiencies? .................................................................................... 12 5. The current event in a longer-term context ..................................................................................................... 14 Tables .............................................................................................................................................................. 16 References and further information ........................................................................................................................... 31 3 Special Climate Statement 66—an abnormally dry period in eastern Australia Introduction The past 12 to 24 months has seen the development of notable dry conditions across much of eastern Australia. Following a generally very wet period from May to September 2016, dry conditions developed in many parts of eastern Australia from late 2016. Tropical Cyclone Debbie and its aftermath brought very heavy rain to many parts of the east coast in March 2017, but in inland eastern Australia, January to September 2017 was a relatively dry period. The last quarter of 2017 was relatively wet in Victoria and the eastern inland, and was marked by a major rain event at the start of December, although that event had little effect on the east coast. Much of tropical inland Queensland had heavy rains in March 2018, but these rains were much less significant south of the Tropic of Capricorn. The most intense dry phase of the recent period began in early 2018. The core of the abnormal dryness was in New South Wales, but other areas were also seriously affected, including southern inland Queensland, and central and east Gippsland in eastern Victoria. As the year continued, despite some winter rains along the southern coastal fringe, significant rainfall deficiencies extended to cover much of Victoria (except for the southwest) and large parts of eastern South Australia. It was also an exceptionally dry period (even by the region's standards) in central Australia. The dry period culminated in September 2018, which was Australia's driest September, and second-driest month, on record. Some areas had useful rains in October 2018, the first month in 2018 in which rainfall averaged over New South Wales was above average, although the heaviest rains occurred in coastal northern New South Wales and the southeast quarter of Queensland, outside the regions worst affected by previous dry conditions. The dry conditions of the last two years follow shortly after long-term rainfall deficiencies in the period from April 2012 to April 2016, which primarily affected two regions; most of inland Queensland (and adjacent border areas of northern New South Wales), and central and western Victoria. The most significant long-term rainfall deficits have occurred in those areas affected by both the 2012-2016 and 2016-2018 dry periods, most notably southern inland Queensland and northern New South Wales. In these areas, below-average rainfall has prevailed for most of the last 6 ½ years, interrupted only briefly by the wet conditions of mid-2016. Northwestern Queensland, which also suffered badly in 2012-16, has had near- or above-average rainfall since 2016, whilst in central and western Victoria, rainfall in 2017 was near or above average before dry conditions returned in 2018. 1. Rainfall deficiencies Significant rainfall deficiencies have occurred during the current event on a range of timescales. Long-term deficiencies, covering the period since 2012, have affected parts of the eastern interior, and central and western Victoria. Deficiencies since the start of 2017 affect most of inland New South Wales, extending into parts of southern Queensland, and have also occurred in Gippsland; in these regions, January to September 2017 and January to September 2018 were both much drier than usual, interrupted by a period of average to above-average rainfall from October to December 2017. Over the 15 months from July 2017 to September 2018, significant rainfall deficiencies occurred in all of these areas, but also extended to coastal areas which had had heavy rain in early 2017, particularly in the Hunter, Sydney and Illawarra regions. For the nine months from January to September 2018, rainfall deficiencies extended to cover almost all of New South Wales, except for coastal areas north of Newcastle and parts of the Australian Alps. They also covered much of southern inland Queensland, most of Victoria away from the southwest, and most of South Australia from Spencer Gulf to the eastern border (except the Lower Southeast district). 1.1. April 2012 to September 2018 (78 months) Long-term rainfall deficiencies, over the period since early 2012, have primarily covered two regions (Figure 1): a large part of inland Queensland, extending north to parts of the north tropical coast around Townsville and south into northern border areas of New South Wales; and much of central and western Victoria. 4 Special Climate Statement 66—an abnormally dry period in eastern Australia Inland Queensland was affected by extensive rainfall deficiencies for the period from April 2012 to April 2016, covering both the northwest and the southern interior. These deficiencies were significantly reduced by heavy (and unseasonable) rains from May to September 2016. From late 2016 onwards, rainfall has remained near or above average in northwest Queensland, bounded to the south approximately by the Tropic of Capricorn, and long-term deficiencies have generally not redeveloped in those areas. However, south of the tropics, dry conditions returned after October 2016 with similar, or in places even greater, intensity to that experienced in the 2012-2016 period, contributing to severe rainfall deficiencies at the multi-year timescale. The worst-affected region has been southern inland Queensland and adjacent northern border areas of New South Wales, where rainfall for the 78-month period has been 20% or more below average. Whilst a dry period of this duration is unusual, it is not unprecedented. Whilst the ranking of the individual events varies from place to place, over much of the affected region (particularly on the Queensland side of the border), the second half of the 1960s were as dry as recent years have been, whilst an even longer dry period extended from the mid-1920s to the mid-1930s. The other large region which has had rainfall deficiencies on this timescale has been central and western Victoria. As in Queensland, consistent dry conditions began in April 2012 (following an extremely wet period in 2010-12) and continued into early 2016, before a very wet winter and spring in 2016. Following a year with generally slightly below average rainfall in 2017, extremely dry conditions redeveloped from the start of 2018 (see section 1.4). The combination of several years of dry conditions from 2012-16 with a very dry 2018 has resulted in substantial multi- year rainfall deficits. Over large parts of central and western