Australian rangelands and climate change – rainfall variability and pasture growth

Australian rangelands and climate change – rainfall variability and pasture growth Report

Climate Change in Australia – Impacts & Adaptation Information for Australia’s NMR Regions

  • Author(s): Bastin, G.
  • Published: 2014
  • Publisher: Rangelands NMR Cluster, Ninti One Limited and CSIRO

Abstract: The frequency of probable past pasture growth events based on daily rainfall gives some indication of what lies ahead for the Rangelands Cluster region under the climate change projection of continuing high natural variability in rainfall. For this analysis, >25 mm of rain over consecutive wet days is considered the minimum requirement for pasture growth to occur across much of the Rangelands Cluster region, and a >50 mm event over the same period should provide ideal growing conditions –particularly where grazed land is maintained in good condition. There are exceptions, of course, to this general guide. Smaller events (e.g. as low as 10 mm) may be effective in cooler weather and for specific locations / vegetation types (e.g. new leaf growth in chenopod shrublands on the Nullarbor Plain).At the other end of the scale, degraded rangeland may respond minimally to >50 mm events. The last 60 years of rainfall data show that periods of rainfall suitable for marginal to ideal growing conditions were infrequent throughout much of the Rangelands Cluster region. The median return period (in days) between >25 mm and >50 mm events lengthens for locations with lower and more variable annual rainfall –that is, to the south (Port Augusta, Cook, Kalgoorlie) and towards the more arid interior (Coober Pedy, Marree, Birdsville, Oodnadatta). The median return period for >50 mm events is close to one year for the more arid parts of the cluster region. Given the highly episodic nature of rainfall across inland Australia, no trends in return period for specific rainfall amounts were detected. The reported probabilities are unlikely to improve under forecast continuing rainfall variability. Projected temperature increases will increase soil moisture losses through greater evaporation and evapotranspiration. This will mean that smaller continuous daily rainfalls (>10 and >25 mm events) will be less effective for pasture growth, particularly during hotter weather. At such times, even >50 mm events that are well separated in time may become marginal for effective growth. In short, a continuing cautious approach to stocking levels, strict control of total grazing pressure and drought preparedness are required into the future. We provide a template spreadsheet for users to calculate their own return-period statistics for any rainfall amount and location where historic daily rainfall data are available. This tool summarises periods of continuous daily rainfall; it cannot calculate rainfall intensity. The URL is http://www.nintione.com.au/resource/AustralianRangelandsAndClimateChange_RainfallVariabilityPastureGrowth_RainfallTemplate.xlsx.

Notes: Associated URL: http://www.nintione.com.au/resource/AustralianRangelandsAndClimateChange_RainfallVariabilityPastureGrowth_RainfallTemplate.xlsx

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Suggested Citation
Bastin, G., 2014, Australian rangelands and climate change – rainfall variability and pasture growth, Report, viewed 09 August 2022, https://www.nintione.com.au/?p=2828.

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