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
The history of Australia's rangelands provides a case study in how the lack of understanding of Australia's climate has led to decisions that have resulted in economic and social 'misfortune', and resource damage in Australia's rangelands. Thus the history of grazing in Australia's rangelands (the main land use on more than 40 per cent of the continent) provides an important case study in terms of the impacts of climate variability and climate change on livestock and economic production, animal welfare, human stresses, resource degradation and government policy. The lessons learnt from how these issues have been addressed in the extensive grazing lands may help the wider community and other industries adapt to future climate variability and change.
Australia's rangelands are characterised by a high temporal variability in rainfall. Fluctuations in Pacific Ocean sea surface temperatures at inter-annual and multi-decadal time scales have been identified as major contributors to year-to-year variability in rainfall across rangelands in eastern Australia and the more general 'drought–flood' perception of Australia's climate. Whilst individual El Niño years have been associated with widespread drought, important sequences of drought years have also occurred during periods of 'neutral' ENSO years, contributing to losses of agricultural production, economic and social stresses, and resource damage (McKeon et al.2004).
A recent report on degradation and recovery in the rangelands describes in detail eight major drought and degradation episodes that have occurred in Australia's grazing lands since the expansion of cattle and sheep numbers in the 1870s (McKeon et al.2004). These episodes involved not only extended drought periods that lasted from four to eight years, but also considerable resource damage in terms of wind and water erosion and infestation by woody and other weeds.
The episodes comprised a general sequence of degradation and partial recovery in which: (1) the population of livestock and other herbivores (rabbits, goats and macropods) built up during sequences of years with above-average rainfall; (2) resource damage occurred due to the high herbivore numbers and intermittent drought; (3) rapid decline in commodity prices for beef and wool occurred devaluing herds and flocks and delaying destocking; (4) severe and extended drought led to heavy utilisation of pasture and further resource damage; and (5) partial resource recovery did not occur until a sequence of above-average rainfall years, which was sometimes decades after the degradation episode.
Despite these painful drought episodes, many graziers have learnt, and documented, how to successfully manage livestock numbers under highly variable climatic and economic conditions. The successful strategies include: (1) maintaining relatively low numbers of livestock (and other herbivores); (2) frequently adjusting livestock and other herbivore numbers to match changing feed availability and responding quickly at the first sign of drought (either as indicated by rainfall deficits or by climate forecasts); and (3) delayed restocking of the resource after drought to allow for recovery of the desired pasture species. Combinations of these strategies have been successful in the highly variable climates (and economies) of Australia's rangelands by conserving pasture and fodder shrubs: thus reducing the impact of rainfall deficits on animal nutrition; minimising the loss of soil carbon and decline in infiltration capacity; and reducing soil erosion. These historical episodes of drought and recovery show that any particular period of drought or dry conditions can be followed by favourable rainfall providing the opportunities to manage for recovery of resource condition and finances. In particular, for eastern Australian rangelands, resource recovery occurred in sequences of wet years that were associated with the interaction of fluctuations in Pacific Ocean sea surface temperatures at different time scales (La Niña years in the cool phase of PDO).
A major development resulting from the drought–degradation episodes was a procedure for objectively estimating the 'safe' grazing capacity of individual properties using historical climate information (Johnston et al.2000). This calculation procedure successfully combined two types of knowledge in the community: (1) the experience and knowledge of successful graziers who have maintained their grazing enterprises through long periods of climate and economic variability; and (2) the capacity to use computer simulation models that were based on scientific grazing trials to calculate pasture growth using historical climate data. This procedure represents a major 'learning from history' experience and provides a potential adaptation response to climate change.
The historical review indicated the information needs (Stone et al.2003) that could have 'softened' the impact of climate variability during these previous degradation episodes. These important information needs may also be appropriate to other enterprises operating in variable climates, and are:
- objective and reproducible monitoring of resource condition and grazing pressure in near 'real-time'
- objective estimates of property 'safe carrying capacity' based on historical rainfall and an ability to extrapolate management practices of long-term successful managers
- knowledge and monitoring of the forces driving climate variability
- climate forecasting or climate risk-assessment systems
- projections of degradation risk combining resource condition, grazing pressure and climate and economic forces
- understanding that the perceived resource resilience partly comes from the climate system and that conservative grazing management can enhance the rate of recovery from inevitable drought periods.