How Extreme South West Rainfall Has Changed It is likely that climate change will be felt most through changes in extreme events.

Trends in Rainfall Events Average number of rainfall days per year in 10 mm intensity bands for 2 epochs. Total rainfall per year in 10 mm intensity bands for 2 epochs. Dark blue: Light blue: Dark blue: Light blue: Perth Airport June and July -

Summer 1-Day Maxima

Winter 1-Day Maxima

Climate Change  A drying trend is indicated for SWWA  Rising temperatures imply increased moisture-carrying capacity –Most models simulate an increase in extreme daily rainfall as a global trend –Can occur even given a drying trend –Not evident in Winter rainfall for SWWA at this time

Linkages & Implications  Links have been found with changes in atmospheric circulation –Likely to be natural variability + enhanced greenhouse effect  Antecedent wetness is generally lower since the rainfall decrease –Negative impact on flood magnitudes of all frequencies  We can say little as yet about very rare events

The Future  Models simulate a drying trend in SWWA  Globally, extreme events can be expected to become more frequent  Projections for regions such as SWWA are not yet clear  Integrating hydrologic and climate models is vital –Long term data sets are crucial

Summary  Winter changes are very subtle  Increase in summer events  Natural variability + enhanced greenhouse effect  Spatial patterns and atmospheric drivers being studied  Very little can be said about rare events –Few data –Limits of modelling capability