Introducing NARCliM1.5: Evaluation and projection of climate extremes for southeast Australia

NARCliM1.5 is the second generation of New South Wales and Australian Regional Climate Modelling (NARCliM) project, which is designed to produce an ensemble of regional climate projections for CORDEX Australasia and southeast Australia. The selected global climate models (GCMs) are used to drive Weather Research and Forecasting (WRF) model for dynamical downscaling. In this study, we evaluate how well the two generations of NARCliM (N1.0 and N1.5) represent the observed record for 12 selected climate extremes and examine their projected changes for southeast Australia. N1.5 ensemble substantially improves upon N1.0 in capturing the spatial patterns of precipitation extremes, however, there is little difference between the two ensembles for temperature extremes. Both N1.0 and N1.5 underestimate dry extreme (consecutive dry day - CDD), hot extremes (warmest daily maximum temperature - TXx, and number of days when maximum temperature is greater than 35 degrees C - TXge35) and daily temperature range (DTR) but overestimate wet extremes (annual sum of daily precipitation above 99th percentile - R99p, consecutive wet days - CWD, days when precipitation is at least 10 mm R10mm, maximum 1-day precipitation - Rx1Day and total wet day precipitation -PRCPTOT) and cold extreme (coldest daily minimum temperature - TNn). N1.0 and N1.5 project different spatial patterns of future changes in precipitation extremes but similar changes in temperature extremes. Differences in climate extremes between N1.0 and N1.5 could be attributed to the driving GCMs. The combined future projections of both N1.0 and N1.5 provide a more complete sampling of the future change space. Future projections indicate that precipitation and temperature extremes will become more intense, raising implications for future planning and risk management.