Developing scenarios of climate change for Southeastern Australia: an example using regional climate model output

Regional climate models nested in global climate models are now being used in Australia to produce high resolution climate change scenarios for use in impact assessments. This paper describes the development of such scenarios for the State of Victoria in Southeastern Australia using the CSIRO Divisi on of Atmospheric Research Limited Area Model (DARLAM) at a horizontal reso lution of 60 km nested in the slab ocean version of the CSIRO global climat e model (GCM). Rainfall and temperature over Victoria are substantially bet ter simulated in DARLAM than they are in the host GCM, although some poor f eatures of the simulation of the seasonal cycle of rainfall have not been i mproved with the increase in resolution. There is evidence to suggest that some of these errors are due to errors in the simulation of atmospheric cir culation provided by the host GCM. Under 2 x CO2 conditions, DARLAM simulat es patterns of rainfall and temperature change which differ significantly f rom those provided by the host GCM and which appear more physically plausib le. In particular, winter rainfall in southern Victoria increases in the DA RLAM simulation, but decreases in the host GCM, Although the DARLAM scenari o could be considered the best single scenario available for Victoria at th e time of its production, it is noted that different, but equally plausible , scenarios could be obtained by nesting DARLAM in other GCMs, or by increa sing the simulation sample size. Our assessment is that the rainfall change s simulated by DARLAM in summer may be most sensitive to such changes. In g eneral, it is concluded that there is great potential to increase the reali sm of climate change scenarios in the Victorian region through careful use of nested regional modelling.