In early 2015, the CSIRO and the BoM released updated national and regional assessments of projected future climate changes over the remainder of the 21st Century. Projections are based on scientific understanding of climate systems, historical trends and model simulations that assess climate response to greenhouse gas emissions. Projections are compared against the climate of the 20-year reference period 1986-20.
Regional assessments summarised below are taken from the CSIRO and BoM report (2015) for the Murray Basin ‘cluster’ of NRM regions (www.climatechangeinaustralia.gov.au). Given the size and climatic diversity of the Murray Basin cluster, the projected climate futures described in the Cluster Report are not specifically applicable to the Mallee region. Even so, the suggested trends can be considered entirely plausible for our region, and have been given a confidence rating to show the level of agreement of projected future climates.
Substantial warming is projected with very high confidence for mean, maximum and minimum temperatures. In 2030, the mean temperature is projected to be 0.6 to 1.3°C warmer than the 1986-2005 reference period. In 2090, it is projected to be between 1.3 to 2.4°C warmer for RCP4.5 (low emissions scenario) and between 2.7 to 4.5°C for RCP8.5 (high emissions scenario).
A substantial increase in the temperature reached on the hottest days, the frequency of hot days and the duration of warm spells are also projected; with a corresponding decrease in the frequency of frost days.
Climate change is not expected to strongly influence changes in annual or season rainfall totals between now and 2030.
However, by 2090 there is high confidence that cool season rainfall will decline and medium confidence that warm season rainfall will remain stable; with the intensity of heavy rainfall events projected to increase.
There is medium confidence that the time spent in drought, and the frequency of extreme drought, will both increase over the course of the century under a RCP8.5 (high emissions).
By 2030, minimal changes are projected for wind speed (high confidence). By 2090, wind speed during the winter is projected to decrease by around 2.5% (medium confidence). Small or inconsistent changes in wind speed are projected for other seasons.
Little change in solar radiation is projected by 2030. By 2090 however, there is high confidence in increased solar radiation during winter (by 15% in a high emissions scenario) and spring (by 7% in a high emissions scenario). Projected changes in summer and autumn radiation are less pronounced.
By 2030, relative humidity is projected to decrease by up to 4%. By 2090, there is medium confidence of a decrease for summer and autumn, and a high confidence of a substantial decrease for winter and spring (up to 8%).
Projections for potential evapotranspiration indicate increases in all seasons. By 2030, potential evapotranspiration is projected to increase by 1 to 7% (3 to 13% for winter). By 2090, the increases are about 1 to 10% (7 to 20% for winter) in a low emissions scenario and 1 to 20% (15 to 40% for winter) in a high emissions scenario.
Soil Moisture and Runoff
While increased potential evapotranspiration and decreased rainfall during winter months will have implications for soil moisture and runoff, it is difficult to determine projections with high confidence. Soil moisture projections suggest overall seasonal decreases by 2090 with medium confidence. Runoff is projected to decrease, but only with low confidence.
Given the strong dependence on the weather, climate changes are expected to significantly impact future bushfires (high confidence of a harsher fire weather climate in the future). There is only low confidence, however, in the magnitude of this harsher fire weather climate, as it is dependent upon rainfall totals and seasonal variation. The enhanced summer rainfall projected in some scenarios could moderate the number of severe fire weather days.