School of Geography, Earth and Atmospheric Sciences - Research Publications
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ItemProjected increases in daily to decadal variability of Asian-Australian monsoon rainfall(AMER GEOPHYSICAL UNION, 2017-06-16)Abstract Changes in rainfall variability in future climate will pose challenges for adaptation. To evaluate changes in Asian‐Australian monsoon wet season rainfall, daily data from historical and future (Representative Concentration Pathway “RCP8.5”) climate simulations are band pass‐filtered to isolate variability on near‐daily, weekly, monthly, intraseasonal, annual, interannual, and decadal time scales. This method is used to quantify changes in variability from 35 coupled climate models for each time scale over the Australian, South Asian, and East Asian monsoon domains. In nearly all cases, the median model change is positive, indicating increased rainfall variability, although with large model spread. The role of increased atmospheric moisture is examined by estimating the change due to an idealized thermodynamic enhancement. This enhancement produces increases in variability that are within the range of the simulated changes under the RCP8.5 scenario, indicating that thermodynamic responses provide a first‐order explanation for the increased daily to decadal monsoon rainfall variability.
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ItemUnderstanding south-east Australian rainfall projection uncertainties: the influence of patterns of projected tropical warming(WILEY, 2017-08)Abstract South‐Eastern Australia and, in particular the state of Victoria, has experienced record deficits of rainfall over the last 20 years, in which the cool part of the year from April to October has been most affected. This situation has created difficulties for water managers, farmers and fire services, with the need to provide more certainty about future climate trends becoming clear. The latest climate projections for South‐Eastern Australia project an overall drying in the cool part of the year with little change in the rest of the year. Although this is in line with current trends, very large uncertainties are associated with these projections. In this study, this range of projections has been investigated, first by assessing how the current suite of climate models simulate the regional rainfall as well as the tropical variability, known to be a key driver of south‐eastern Australian climate. The models were found to be reasonable overall, although a number overestimate Victorian summer rainfall. Model rainfall projections are found to be related to the models' projected patterns of tropical warming, where 60% of the range in cool season rainfall projections can be explained by the range of pattern of tropical changes. In addition, the projected drying tends to be more intense in the models best able to simulate summer rainfall, thus suggesting that the upper end of the uncertainty range is less likely to be realized as it may reflect inherent model biases, rather than physical changes.
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ItemNo Preview AvailableSouthern Hemisphere subtropical drying as a transient response to warming(NATURE PUBLISHING GROUP, 2019-03)Climate projections1–3 and observations over recent decades4,5 indicate that precipitation in subtropical latitudes declines in response to anthropogenic warming, with significant implications for food production and population sustainability. However, this conclusion is derived from emissions scenarios with rapidly increasing radiative forcing to the year 21001,2, which may represent very different conditions from both past and future ‘equilibrium’ warmer climates. Here, we examine multi-century future climate simulations and show that in the Southern Hemisphere subtropical drying ceases soon after global temperature stabilizes. Our results suggest that twenty-first century Southern Hemisphere subtropical drying is not a feature of warm climates per se, but is primarily a response to rapidly rising forcing and global temperatures, as tropical sea-surface temperatures rise more than southern subtropical sea-surface temperatures under transient warming. Subtropical drying may therefore be a temporary response to rapid warming: as greenhouse gas concentrations and global temperatures stabilize, Southern Hemisphere subtropical regions may experience positive precipitation trends.