Trends in rainfall associated with sources of air pollution

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 degrees 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 similar to 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.