Trends in rainfall associated with sources of air pollution

E.Keith Bigg

doi:10.1071/EN07086

RESEARCH ARTICLE

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Trends in rainfall associated with sources of air pollution

E.Keith Bigg

+ Author Affiliations

- Author Affiliations

12 Wills Ave., Castle Hill NSW 2154, Australia. Email: keith@hotkey.net.au

Environmental Chemistry 5(3) 184-193 https://doi.org/10.1071/EN07086
Submitted: 28 November 2007 Accepted: 13 April 2008 Published: 19 June 2008

Environmental context. Decreasing trends in rainfall over large areas of eastern and south-western Australia have resulted in critical water shortages. Three reasons have been suggested. The first is a change in atmospheric circulation as a result of greenhouse gas forcing. The second is that changes in land usage have affected surface moisture, albedo and cloud formation. Another, the subject of this study, is that airborne particulates associated with urban areas have acted to decrease the mean efficiency of rainfall, the growth of urban areas thereby causing an underlying decreasing trend in rainfall.

Abstract. Trends in rainfall in the 35 years 1970–2004 have been calculated for all 350 available rainfall stations having sufficiently complete records that lie between latitudes 26–30°S and longitudes 150–154°E. The area contains two major urban centers, Brisbane with a rapidly growing population approaching two million and the Gold Coast with a population of ~500 000. Statistically highly significant negative trends were found in the vicinity of Brisbane, with decreases exceeding 40% of mean daily rainfall in the 35 years, and in a smaller area inland from the Gold Coast. The spatial distribution of trends was consistent with aerosol production from human activities, the prevailing winds and losses due to the topography. A previously published observation using satellite data showed that cloud properties were affected by urban aerosols in a way that is likely to reduce precipitation. The results of this study reinforce the suggestion made then that monitoring of aerosol concentrations and properties and in-situ observations of rain formation processes in the area should be undertaken as a matter of urgency.

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Appendix A1.

**Table A1. List of stations and their statistics**
Columns: A, Bureau of Meteorology’s site identifying number; B, latitude, degrees; C, longitude degrees east; D, trend, change in 35 years expressed as a percentage of mean daily rain 1970–2004 for the site; E, correlation coefficient of the trend; F, statistical significance of the correlation; G, mean daily rainfall 1970–2004 (mm); H, years omitted from the analysis because of missing or bad data