Abstract
Annual rainfall and the seasonality of rainfall during a year are important drivers of agricultural productivity and profitability in Australian agriculture. Historic trend detection can give insights into significant and prolonged changes that might continue in the future and are of relevance to agriculture. Here we complement the analysis of historic data with climate projections from global climate models. We use gridded and station rainfall data for three study areas in the Australian midlatitudes, between 24°S and 35°S. Total summer and winter rainfall, annual total rainfall and annual rainfall extreme indices are calculated for the period 1907 to 2018. Historic trends are analysed with statistical significance tests of linear trends and rainfall deciles. Future trends are analysed for annual, summer and winter rainfall for three time periods, 2020–2039, 2040–2059 and 2060–79, as the ensemble of 25–37 global climate models. Summer rainfall in the Western Australia wheat belt increased by 0.18–0.21 mm per year. Winter rainfall decreased by 0.42–0.43 mm per year. Parts of northern New South Wales (NSW) experienced an exceptionally dry decade, 2011–2020 with summer rainfall 50–200 mm below the long-term average. Future rainfall projections for the wheat belt show a strong declining trend, irrespective of the climate scenario, while in the other two regions, increases and decreases are possible. We confirm previous findings of declines in winter rainfall in the Western Australia wheat Belt but do not detect any such changes in Eastern Australia. Some of the observed long periods of dry summers in northern NSW are rather unprecedented. Future studies should repeat the trend analysis for Eastern Australia as the data becomes available. Apart from climate indices, agrometeorological indices for specific agricultural commodities should be developed and used in trend analysis.
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Data availability
Waha, Katharina; Ord, Louise; Alexander, Lisa; Parisi, Irene (2021): Australian Midlatitudes Rainfall. v15. CSIRO. Data Collection. https://doi.org/10.25919/qdk0-ys13.
Materials availability
An interactive web application to query and view the rainfall data for selected locations is available at https://shiny.csiro.au/rainfall-trend-explorer/. Please cite the tool as Ord, Louise; Waha, Katharina (2021): Australian Rainfall Trend Explorer. v5. CSIRO. Service Collection. http://hdl.handle.net/102.100.100/390056?index=1.
Code availability
Not applicable.
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Acknowledgements
We are grateful to Lisa Alexander from UNSW for providing the AWAP-EX dataset and help with advice on HadEX data for extreme rainfall indices. We thank Blair Trewin from the Bureau of Meteorology for kindly helping to select the weather stations for this study. We thank Jon Welsh, AgEcon, and Russell Pattinson, Miracle Dog, for informing the selection of study areas and study sites and reviewing the results of the historical trend analysis. We are grateful to Jaci Brown from CSIRO for providing feedback on the design of the study and an earlier version of the manuscript.
Funding
KW, JC and CH have received funding from the Managing Climate Variability Research & Development Programme (project no B.CCH.2111 Changes in summer rainfall and implications for agriculture).
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KW designed the study and research questions and selected the study areas. KW, MF and IP collected secondary data for historic rainfall and rainfall drivers and KW, IP and MP did the data analysis for historic rainfall trends. IP summarized the first results of the analyses and KW wrote the manuscript based on that. JC and CH analysed future rainfall projections and prepared the respective plots and text describing the results. EV and KD discussed the initial study design and focus with KW. All authors contributed to internal review and discussion of the results multiple times.
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Waha, K., Clarke, J., Dayal, K. et al. Past and future rainfall changes in the Australian midlatitudes and implications for agriculture. Climatic Change 170, 29 (2022). https://doi.org/10.1007/s10584-021-03301-y
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DOI: https://doi.org/10.1007/s10584-021-03301-y
Keywords
- Seasonal rainfall change
- Historic rainfall trend
- Future rainfall trends
- Drought