An investigation of severe hailstorm activity under present and future climate conditions over the greater Sydney region

The main aim of this study is to present the results of an investigation of the possible changes in the behavior of severe hailstorms that affect the central eastern coast of Australia, under future climate conditions. The main focus is on the most heavily populated region of Australia, namely, the Greater Sydney region. The model used here is the recently developed University of Oklahoma Coupled General Circulation Model, known as OU-CGCM. The OU-CGCM can also be run as a high resolution NWP model, employing a hierarchy of nested model domains, with a sophisticated cloud microphysics scheme in the highest resolution domain (1 km horizontal grid spacing) of the model. The study compares a range of current climate simulations with future climate simulations that utilise the one of several possible IPCC climate change scenarios, namely IS92a, to detect likely significant trends in frequency, intensity, duration, and tracks of hail storms under those future climate conditions. The entire study spanned a 90-year period from 1960 through to 2050, with the first three decades used for model spin-up. The fourth decade, the 1990s, provided a reference period to compare the high resolution modeling case studies with the observed hail storms that actually occurred in the Greater Sydney region. The modeling case studies are those of the four most severe storms that occurred in the Greater Sydney region in the 1990s. The period from the 1990s to 2002 also provided a link between the current and the future climate model runs, the future climate runs being defined as occurring during the fifty year period 2000-2050.

This work adds to some very recent hail modeling case studies of severe hailstorms over eastern New South Wales carried out by the authors and also complements the future hail climate studies undertaken by other researchers whose work focussed on the eastern south coast of Australia.