Australian climate extremes in the 21st century according to a regional climate model ensemble: implications for health and agriculture.

The negative impacts of climate extremes on socioeconomic sectors in Australia makes understanding their behaviour under future climate change necessary for regional planning. Providing robust and actionable climate information at regional scales relies on the downscaling of global climate model data and its translation into impact-relevant information. The New South Wales/Australian Capital Territory Regional Climate Modelling (NARCliM) project contains downscaled climate data over all of Australia at a 50 km resolution, with ensembles of simulations for the recent past (1990–2009), near future (2020–2039) and far future (2060–2079). Here we calculate and examine sector-relevant indices of climate extremes recommended by the Expert Team on Sector- specific Climate Indices (ET-SCI). We demonstrate the utility of NARCliM and the ET-SCI indices in under- standing how future changes in climate extremes could impact aspects of the health and agricultural sectors in Australia. Consistent with previous climate projections, our results indicate that increases in heat and drought related extremes throughout the 21st century will occur. In the far future, maximum day time temperatures are projected
to increase by up to 3.5 C depending on season and location. The number of heatwaves and the duration of the most intense heatwaves will increase significantly in the near and far future, with greater increases in the north than south. All capital cities are projected to experience at least a tripling of heatwave days each year by the far future, compared to the recent past. Applying published heat-health relationships to projected changes in tem- perature shows that increases in mortality due to high temperatures for all cities examined would occur if pro- jected future climates occurred today. Drought and the number of days above 30
C are also projected to increase over the major wheat-growing regions of the country, particularly during spring when sensitivity of wheat to heat stress is greatest. Assuming no adaptation or acclimatisation, published statistical relationships between drought and national wheat yield suggest that national yields will have a less than one quarter chance of exceeding the annual historical average under far future precipitation change (excluding impacts of future temperature change and CO2 fertilization). The NARCliM data examined here, along with the ET-SCI indices calculated, provide a powerful and publicly available dataset for regional planning against future changes in climate extremes.

Fig. 6. Multi-model means of the Standardised Precipitation-Evapotranspiration Index (SPEI; section 2.3) for each season. Top row: near-future, bottom row: far- future. First column: DJF, second column: MAM, third column: JJA, fourth column: SON. A base period of 1990–2009 (i.e. the recent past) is used to calculate SPEI for all time periods. Thus, by definition the SPEI is close to zero during the recent past and excluded here. Future values should be interpreted as increases or decreases in drought conditions relative to the recent past. See Table 2 for an interpretation of drought intensity. Stippling indicates significant change (section 2.4 for method). Values at the top right of each panel represent the minimum, mean and maximum of the plotted field.