Living in a variable climate
Dr Greg McKeon, CRC for Greenhouse Accounting, Queensland Department of Natural Resources and Water
prepared for the 2006 Australian State of the Environment Committee, 2006
In the past, the extent of the impacts of each drought period has usually not been documented until after the event, when sufficient information becomes available. Not surprisingly then, there appears to be a need during each drought event to describe it as the worst in 'a very long time' (a decade, generation, lifetime, century, since records began), perhaps to jolt the wider community into action and support. The 2001–05 drought has also been shaping the debate in the wider community in terms of expectations on appropriate drought management practices, land and water use, and government support (Botterill 2003, McColl and Young 2005). In the following section the current drought (2001–05) is reviewed from the perspectives of historical droughts and future climate change. The following review was prepared in October 2005. Important updates of the impacts of continuing drought conditions can be found in Watkins (2005) and Bureau of Meteorology (2006).
The so-called 'millennium' drought (Whitaker 2005, p. 220) commenced in 2000 in regions across Australia (Figure 5) and has been a major cause of hardship for rural and urban communities. It should be noted that the term 'millennium drought' reflects its timing in terms of dates not its implied frequency. The assessment of the drought's severity in relation to historical variability is important in the context of monitoring the emerging impact of climate change. The drought period commenced after a sequence of above-average years of rainfall (1998–99 to 2000–01). The effect of the drought occurred earlier (2000) in the south-west of Western Australia impacting on water inflow into dams and grain production (Stephens et al. 2003). In 2001–02 there were high commodity prices, and incomes for many farms were at record levels (Martin et al. 2005, p. 23). Important exceptions during this period, as discussed above, are south-eastern and coastal Queensland and south-western Australia, which have experienced drier conditions for at least the last 15 years. In 2001–02, drought began in areas of south-western Queensland, western New South Wales, eastern South Australia, north-western Victoria and the Gascoyne region of Western Australia. In eastern Australian rangelands, the previous sequence of favourable years had led to a build up in kangaroo numbers (Stone et al.2003) and, with emerging drought conditions, high grazing pressure in rangeland areas became apparent. In 2002–03, an El Niño year, extreme drought occurred across much of eastern Australia and areas of Western Australia, further exacerbating drought conditions in those areas where the drought had already commenced (McKeon et al. 2004). The year 2002 had the highest daytime average temperature aggregated across Australia. 'The impact of the rainfall deficiencies was exacerbated by high [potential] evaporation rates in response to the very high daytime temperatures' (Bureau of Meteorology, 2002, p. 10).
A substantial number of regional submissions for declaration of Exceptional Circumstances commenced towards the end of 2002. By August 2003, more than 80 per cent of New South Wales was declared to be under Exceptional Circumstances. In October 2002, the Farmhand Foundation organised financial support from the wider community and started a public debate on issues such as 'drought-proofing' Australia (Hayman 2003, p. 16; the debate regarding drought-proofing is further discussed below). The statewide retention rate of livestock in New South Wales, a major livestock producing state, was 'surprisingly high' (71 per cent of sheep and 75 per cent of cattle, Hayman 2003, p. 15) placing a potentially high feeding cost on livestock producers. In contrast, there were substantial reductions in livestock numbers in several rangeland regions across Australia. For example, sheep numbers in the western districts (i.e. rangelands) of New South Wales had been reduced to 30-40 per cent of pre-drought numbers and were lower than reported in 1902, at the end of the extended Federation drought. Whilst indicating the severity of the 'millennium' drought, this response also suggests an improvement in the management for drought compared to previous historical drought and degradation episodes in the rangelands, when stock were retained too long (McKeon et al. 2004).
The millennium drought also had important impacts on urban water availability and property damage (Watkins 2005). For example, associated with the extreme dry conditions, there were very destructive bushfires. In Canberra in January 2003, fires resulted in the loss of lives and property as described in Beer (2006).
With the general warming trend of the Australian continent since 1910, a major concern for agriculture and biodiversity is the possibility that the impact of drought will be amplified by higher temperatures and potential evaporation rates. Nicholls (2003) evaluated the 2002 drought in terms of its historical climate context, asking whether the 2002 drought was the worst. He found that the severe 1940 drought in the Murray Darling Basin was 0.6°C cooler than 2002 and was also restricted to the southern half of the country. Nicholls (2003, p. 3) concluded, 'on these broader comparisons, the combination of extreme temperatures with low rainfall during 2002 does seem unique even if, on shorter averaging periods and smaller scales, similar high temperature – low rainfall combinations have occurred in the past.' Nicholls (2003) examined possible causes of high temperatures in 2002 by comparing maximum temperatures with rainfall (from 1952 to 2002). He showed that droughts were in fact becoming warmer and that the nature of droughts in eastern Australia was changing over the last 50 years. 'The apparently inexorable warming from the mid-20th century has meant that each drought was warmer than the previous drought, both during the daytime and at night' (p. 5). He noted that the warming over Australia over the past century matched global warming and stated carefully that 'the possibility that the warming observed over Australia, with its consequent effects on the 2002 drought, is also likely due to the enhanced greenhouse effect warrants consideration' (p. 5).
Source: From poster 'Australia's Variable Rainfall' www.LongPaddock.qld.gov.au. Queensland Department of Natural Resources, Mines and Water using rainfall data from Australian Bureau of Meteorology.
Assessment of the drought in terms of the other factors that affect potential evaporation (solar radiation, vapour pressure deficit and wind) are yet to be completed, but it is necessary to determine to what extent the observed warming reduced soil moisture availability and hence amplified the damaging effects of low rainfall on agricultural production. Nevertheless, should the 'warming' of droughts continue, then 2002 could well be seen, with the benefit of hindsight, as the forerunner of things to come.
Further record high temperatures occurred in January to April 2005, exacerbating dry conditions across much of Australia (Bureau of Meteorology 2005). April 2005 was, in terms of maximum temperature anomaly, the “hottest April on record by a considerable margin for Australia and also across, NSW, Victoria, SA and the NT” (Bureau of Meteorology 2005). Similarly, the average Australian April minimum temperature was also the highest on record. The occurrence of these types of extremes, coupled with an expectation of global warming trends, provides powerful examples supporting the urgency for developing future adaptation strategies.
Following average conditions in 2003–04, severe drought returned in many regions of Australia in 2004–05 (a year with marginal El Niño conditions). For many regions, the overall five-year period from 1 April 2000 to 31 March 2005 had extremely low rainfall compared with historical records of 115 years commencing in 1890. The severity and duration of the millennium drought invites comparisons with the seven year Federation drought (mid/late 1890s, early 1900s). The Federation drought was particularly severe and protracted across eastern Australia. Extremely low rainfall (less than Decile 1) was also recorded in many regions across the continent during this period. For the 5-year periods ending in March 2005 and March 2006, some stations have recorded lower rainfall than in the Federation drought, for example, in 2005 south-west Western Australia and south-eastern Queensland; and in 2006 south-west Queensland, central coastal Queensland and areas of south-eastern Australia. However, it should be noted that the Federation drought in eastern Australia spanned seven years with severe rainfall deficits in many regions across Australia. As a result this difficult period in our history remains a benchmark for planning and climate risk management.
It is difficult to compare how well droughts have been managed over the last hundred years, given the many changes that have occurred in: drought management practices; infrastructure developments such as dams and transport; rural populations; commodity prices; property size and land use; the contribution of agriculture to the national economy; and government provision of financial support. Responses to, and features of, the current drought that have probably reduced its impact on resource condition and farm financial performance include: awareness of seasonal climate forecasts based on El Niño development in 2002 (Stephens et al. 2003), and to a lesser extent in 2004; early reductions in stock numbers reducing resource damage in rangeland regions; use of farm management deposits 'to manage exposure to adverse economic events and seasonal fluctuations' (Martin et al. 2005, p. 23); substantial government support 'targeting farm business and welfare needs of farming families' (Martin et al.2005, p. 20); and relatively high prices in historical terms for livestock and grains 'assisting farmers to manage cash-flow at a time of reduced production' (Martin et al.2005, p. 1).
To better monitor and document the impact of drought and streamline Exceptional Circumstances application and assessment processes, a National Agricultural Monitoring Systems (NAMS) has been developed. NAMS contains current and historical climate data, model output and remotely sensed information to indicate the agricultural and financial impact of current seasonal conditions and to place these in an historical context.
A feature of the current drought has been a renewal of the debate on 'drought proofing' agriculture and rural Australia. 'Drought proofing' describes the concept of changing management practices and infrastructure to reduce the impact of drought on production and communities. At the core of the debate is the clash between two opposing approaches to managing for drought. On one hand, it is argued that technical advances (drought-adapted crop varieties, water storage for irrigation) and financial support are needed to maintain a high level of agricultural production and to protect the stability of rural communities in periods of rainfall deficit. On the other hand, there is a call for the recognition that Australia has a relatively high frequency of drought occurrence in many regions and that agricultural enterprises and practices, financial management options, and structural adjustment support should reflect a more conservative expectation of resource use. This latter view argues that better individual climate risk management and more appropriate land use would be less environmentally damaging and require less financial support.
This commentary does not seek to resolve this hundred-year-old debate. Nevertheless, the transparent debate is, in itself, a feature of successful adaptation to 'living in a variable climate' in that the ideological views on land and water use that dominated agricultural development since settlement can at least now be evaluated from scientific and economic perspectives (for example, McColl and Young 2005). To this end, the continued monitoring of environmental indicators and the separation of climate and management effects represent the next major challenges for environmental science.