Climate and Water Outlook, March-May 2018
By Micah Moen
Welcome to the Climate and Water Outlook for Autumn 2018. Summer has been exceptionally warm and dry for much of eastern Australia, while there’s been record-breaking rainfall in the tropical north of Western Australia. Autumn is looking warm and dry for many areas, with odds favouring a delayed autumn break for the southern cropping season. But first, let’s look at recent conditions. Three tropical cyclones have brought plenty of rain to parts of Western Australia and the Northern Territory this summer. Broome has already had its wettest year on record, with over 1.5 m of rainfall and widespread flooding. The very late and weak La Niña brought little rain to eastern Australia. Western Queensland was hardest hit, and hasn’t had above-average summer rains now for six years. While the rain kept temperatures down in the west, summer in the eastern two-thirds of the country was much warmer than average. The average temperature across the whole of Queensland exceeded 40°C on two consecutive days in February, with the State average of 40.5°C on the 12th being Queensland’s hottest ever February day. Hot and dry conditions over summer resulted in a significant number of bushfires in eastern Australia —particularly New South Wales. The fire season certainly isn’t over yet, so keep your bushfire plan up to date. Lower-layer soils in eastern Australia are
very much drier than usual —particularly in the Hunter Valley in New South Wales, where warm conditions and very low rainfall have led to extremely dry soils. The dry soils in the east mean when rains do come, they will first soak into the soils before any increase is seen in runoff into water storages. Water levels in the Murray–Darling Basin and southern Victoria remain lower than at this time last year. But levels in Tasmania and the southwest of Western Australia remain higher than last February. So what’s driving our climate right now? In the Pacific Ocean, the weak La Niña pattern is breaking down. Patterns in the Indian Ocean are already neutral, and look likely to stay that way through autumn. But in the Tasman Sea, sea surface temperatures are currently the most above-average on the globe. This could feed extra moisture into any East Coast Lows that develop later in autumn or winter. So what typically happens in autumn after a weak La Niña ends? The five most similar events ended drier than average over parts of central and eastern Australia. This is reflected in our rainfall outlook for this autumn, with drier-than-average conditions likely for central parts of Australia. Given this outlook, and the long-term trend for drier autumn and early winter periods, odds favour an average or later-than-average autumn break for parts of southern Australia. Looking at streamflows: Low or near-median flows are likely at most locations —generally in the south and east, where soils are dry. High streamflows are likely in the tropical north after the recent monsoonal rains. In terms of temperatures: Autumn days and nights are likely to be warmer than average for much of Australia. Heatwaves can continue into autumn, particularly in areas with dry soils. So in summary: Autumn is likely to be drier than average for large parts of Australia; temperatures are likely to be warmer than average;
low or near-median streamflows are likely at most locations, with high streamflows
in the tropical north; and the timing of the autumn break for cropping in southern Australia may well be normal or later than usual. For more details, visit our website at bom.gov.au/climate/ahead. You can also get updates via Facebook and Twitter. Our first look at likely conditions for April–June will be available on Thursday 15 March. For the Bureau of Meteorology, I’m Andrew Watkins.