Degree Name

Doctor of Philosophy


School of Geosciences


Thunderstorm rainfall is considered as a very vital climatic factor because of its significant effects and often disastrous consequences upon people and the natural environment in the Greater Sydney Region. Thus, this study investigates the following aspects of thunderstorm rainfall climatology of the region between 1960 to 1993.

In detail, it was found that thunderstorm rainfalls in Sydney have marked diurnal and seasonal variations. They are most frequent in the spring and summer and during the late afternoon and early evening. Thunderstorms occur primarily over the coastal areas and mountains, and less frequently over the lowland interior of the Sydney basin. Environmental factors, such as the local climatic factors and physiographic parameters may control thunderstorm occurrence and its associated rainfall distribution. More detailed associations, possible causal relationships, using stepwise regression indicate that thunderstorm rainfall frequency could partially be affected by air and sea temperatures, and air humidity.

Accordingly, specific attention was paid to the patterns of the spatial variation of thunderstorm rainfall during the warm months (October to March) over a long timespan (34 years), using data from 191 rainfall stations. Mathematically, the gamma functions (beta and alpha values) describe and summarise the probability distribution of daily thunderstorm rainfall across the Sydney region. The findings reveal the interplay of topographic, coastal and urban effects in controlling the amount of thunderstorm rainfall in both spring and summer.

A "climatologically oriented GIS" (including a Digital Elevation Model (DEM), a proximity map, and a landuse model) together with regression procedures were used to assess the relative importance of physiographic and environmental variables for six of the largest thunderstorm rainfall events. Three patterns emerged. The first is an increase in thunderstorm rainfall occurring toward the coast. The second is an increase in thunderstorm rainfall as elevation increases. Finally, the more compact the urban residential and commercialised areas the greater the amount of thunderstorm rainfall. These variables account for 70 per cent of thunderstorm rainfall variations throughout the Sydney region.