WRF simulations of future changes in rainfall IFD curves over Greater Sydney.

The Weather Research and Forecasting (WRF) model has been used at convection-permitting resolution (2km) to simulate the future climate of the greater Sydney region with a focus on precipitation extremes at durations from 1 hour to 1 day. Overall, the simulations project temperature increases of 1 to 2 C, with larger increases in autumn and winter compared to spring and summer. In terms of precipitation most of the domain is projected to see annual increases of up to 40%. These increases occur mostly in autumn, with little change in summer. Extreme precipitation (higher than 95th percentile) is projected to contribute a larger proportion of this precipitation total. While the model can reasonably reproduce medium extremes (like the 95th percentile), annual maxima precipitation time-series contains significant over-estimation for much of the area of interest. Given this model limitation, the area-averaged rainfall Intensity-Frequency-Duration (IFD) curves are simulated reasonably well at large Annual Exceedence Probabilities (AEPs) (50%) and show progressively larger errors for rarer AEPs. Future projections show rainfall depths increasing for all durations and AEPs considered here. This future increase is larger for rarer AEPs, but relatively consistent across durations.

Figure 4 Domain average IFD curves for bias corrected WRF: 1990-2009 (solid lines) and 2040- 2059 (dashed lines).