11.7 Australia – New Zealand
Assessment of projected climate change for Australia and New Zealand:
All of Australia and New Zealand are very likely to warm during this century, with amplitude somewhat larger than that of the surrounding oceans, but comparable overall to the global mean warming. The warming is smaller in the south, especially in winter, with the warming in the South Island of New Zealand likely to remain smaller than the global mean. Increased frequency of extreme high daily temperatures in Australia and New Zealand, and decrease in the frequency of cold extremes is very likely.
Precipitation is likely to decrease in southern Australia in winter and spring. Precipitation is very likely to decrease in south-western Australia in winter. Precipitation is likely to increase in the west of the South Island of New Zealand. Changes in rainfall in northern and central Australia are uncertain. Extremes of daily precipitation are very likely to increase. The effect may be offset or reversed in areas of significant decrease in mean rainfall (southern Australian in winter and spring). An increase in potential evaporation is likely. Increased risk of drought in southern areas of Australia is likely.
Increased mean wind speed across the Southern Island of New Zealand, particularly in winter, is likely.
Significant factors contribute to uncertainty in projected climate change for the region. The El Niño-Southern Oscillation significantly influences rainfall, drought and tropical cyclone behaviour in the region and it is uncertain how ENSO will change in the future. Monsoon rainfall simulations and projections vary substantially from model to model, thus we have little confidence in model precipitation projections for northern Australia. More broadly, across the continent summer rainfall projections vary substantially from model to model, reducing confidence in their reliability. In addition, no detailed assessment of MMD model performance over Australia or New Zealand is available, which hinders efforts to establish the reliability of projections from these models. Finally, downscaling of MMD model projections are not yet available for New Zealand but are much needed because of the strong topographical control of New Zealand rainfall.