Ground Cover Supplement : GC Supplement - Climate forecasting
13 extreme weather Growers face three interrelated climate risks: running out of moisture, frost and spring heat events. Research in South Australia is examining the risk of damaging heat events on wheat production. It is hoped the research will lead to heat stress ratings similar to those being developed for frost. the chance of having an extremely hot week nearly doubles across much of southern australia during spring months when there are el niño conditions. el niño conditions are associated with extensive warming of the sea surface in the central and eastern tropical Pacific, whereas la niña is associated with extensive cooling. FIGURE 1 Regions of increasing August to November frosts. SOURCE: DR STEVEN CRIMP 0 600 1000km Regions circled in black dashes represent areas of increasing August–November frosts 0.044 0.067 plants coping better with heat stress as grain-fill advanced. a single hot day of 35°c to 36°c during flowering decreased yield by as much as 20 per cent. information on the likelihood of heat events and their impact on wheat yield was presented at grower meetings as part of a discussion on managing climate risk. Historical analysis of the first date of heat events in spring and comparisons between regions was of particular interest. Discussions centred on best-bet risk-management strategies regarding variety choice and flowering time. there is a need for ongoing research to quantify the impact of hot days on the australian grainbelt. More and later Frosts – steven CrIMp it is a cruel paradox that although australia’s climate is warming, the number of frost days and the length of the frost season have increased across much of the australian grainbelt (figure 1). csiro analysis of climate data between 1960 and 2011 suggests the increasing frost incidence is due to the presence of more highs centred further south (37.5°s) and further west (125°e) and to the existence of more el Niño conditions during this period. the southern shifting highs bring air masses from further south than in the past. this air is very cold and leads to extensive frosts. scientists think this so-called ‘southward displacement’ is what is driving the changing frost patterns. Modelling work indicates that the increased incidence of frosts in august is likely to remain around current levels until the mid-2030s. along with an increased incidence of frosts between august and November there has also been a shift in frost occurrence to later in the year. in the east the window of frost occurrence has broadened, so frosts are occurring both earlier and much later in the season. in the west there is less occurrence of earlier frosts and more of a shift to frosts later into the season. the frost window has lengthened by three weeks in the Victorian grainbelt and by two weeks in the New south wales grainbelt. western australia has, statistically, remained the same, while eastern sa sites are similar to Victoria and sites in the west of sa are more like wa. Northern Victoria seems to be the epicentre of the change in frost occurrence. analysis of long-term temperature data for longerenong in the Victorian wimmera indicates the incidence of moderate (2°c) and extreme (0°c) frosts during the wheat flowering window has increased in the past 15 years (figure 1). the frost window over much of northern Victoria lengthened considerably in the decade to 2011 and is much wider than growers have experienced previously. the 10 per cent risk of experiencing a 2°c minimum temperature event, now occurs 46 days later than in any of the previous decades. □ grDC research Codes CsP00125, mCv00010, mCv00037 more information: Dr Peter Hayman, SARDI, 08 8303 9729, firstname.lastname@example.org; Steven Crimp, CSIRO, 02 6246 4095, email@example.com weather Patterns Weather patterns across the southern Australian grainbelt are influenced by two dominant drivers: a cold maritime influence from the south and a warm to hot continental influence from the north. Heat events in spring coincide with a high-pressure system to the east and an approaching cold front. This combination leads to a northerly flow of air (and associated hot conditions) followed by a south-westerly (associated cool conditions). In spring the systems tend to move relatively quickly, leading to heat spikes rather than the summer heat waves. It is not unusual for the cold front to be followed by a high- pressure system and a radiation frost.
GC Supplement - Grain and Graze
GC Supplement - Profitable pulses and pastures