Persistence of cool conditions after heavy rain in Australia

Abstract

There is a general understanding that heavy rainfall will suppress subsequent near-surface temperatures. However, there have been few studies describing this effect. In this study the top 10 % of monthly rainfall, by season and by grid point over Australia is used to represent extended periods of heavy rainfall (termed 'very wet'). The corresponding daily maximum average monthly temperature (Tmax) during those months are shown to be cooler by at least 0.5 °C almost everywhere across Australia, in every season in both observation-based data and climate models. Cooler than average Tmax conditions are then evident for the following four months in some places, particularly following very wet months in winter. The average monthly daily minimum temperature (Tmin), unlike Tmax, is warmer than average during very wet months in winter,by up to 1.5 °C in the east of the continent in both observations and the model mean. Warmer Tmin conditions are also evident during very wet months in the south-east and across the south of the continent in other seasons, particularly in observations. Tmin is cooler than average in very wet months in summer elsewhere across the continent. In subsequent months, Tmin then tends to be cooler than average. It is suspected that increased cloud during the first month keeps Tmin warm, while wetter soils contribute to cooler Tmin during subsequent months. These results indicate that indeed heavy, extended rainfall can have a cooling influence on subsequent temperature, and, following winter, this can have an effect right through to the following summer. The Tmax anomalies at the end of the century under RCP8.5 are similar to those under the current climate, except in future there are relatively cooler conditions in the south during very wet months in winter and in the month following.