89 research outputs found
The climate of the Eastern Seaboard of Australia: A challenging entity now and for future projections
No full text
2006), Attribution of the late 20th century rainfall decline in South-West
No full textAbstract: There has been a dramatic decrease in rainfall in the South-West of Australia (SWA) since the mid 1960s. A statistical method, based on the idea of analogous synoptic situations, is used to help clarify the cause of the drying. The method is designed to circumvent error in the rainfall simulated directly by a climate model, and to exploit the ability of the model to simulate large-scale fields reasonably well. The method uses relationships between patterns of various atmospheric fields with station records of rainfall, to simulate the local rainfall variability. The original technique was developed in a previous study. Here it is modified for application to two ensembles (each of four members) of simulations of the past century performed with the Parallel Climate Model (PCM). The first, called "Natural", is forced with natural variations in both volcanic activity and solar forcing. The second, called "Full Forcing" also includes three types of human-induced forcing resulting in trends in greenhouse gases, ozone and aerosols. "Full Forcing" provides a better match to observational changes in sea surface temperature in the vicinity of SWA. However, it is not possible to discriminate between the two ensembles which one match the observed decline. There is a hint that the fully forced ensemble is more realistic, but it is nothing more than a hint. The downscaling approach, on the other hand, provides a much more accurate reproduction of the day to day variability of rainfall in SWA than does the rainfall simulated directly by the model. The downscaled ensemble mean rainfall in "Full Forcing" declines over the region with a spatial pattern that is similar to the observed. This contrasts with an increase of rainfall in the downscaled rainfall in the "Natural" ensemble. These results give the clearest indication yet that anthropogenic forcing played a role in the drying of SWA. Note, however, that ambiguity remains. For example, although the observed decline fit within the range of downscaled model simulation, the ensemble mean rainfall decline is only about one half of the observed estimate, the timing differs from the observations, drying did not occur in the downscaling of one of the four "Full Forced" ensemble members, and not all potential forcing mechanisms are included in "Full Forcing" e.g. land surface changes
Attribution of the Late-Twentieth-Century Rainfall Decline in Southwest Australia
No full textThere was a dramatic decrease in rainfall in the southwest of Australia (SWA) in the mid-1960s. A statistical method, based on the idea of analogous synoptic situations, is used to help clarify the cause of the drying. The method is designed to circumvent error in the rainfall simulated directly by a climate model, and to exploit the ability of the model to simulate large-scale fields reasonably well. The method uses relationships between patterns of various atmospheric fields with station records of rainfall to improve the simulation of the local rainfall spatial variability. The original technique was developed in a previous study. It is modified here for application to two four-member ensembles of simulations of the climate from 1870 to 1999 performed with the Parallel Climate Model (PCM). The first ensemble, called natural, is forced with natural variations in both volcanic activity and solar forcing. The second ensemble, called full forcing, also includes three types of human-induced forcing resulting from changes in greenhouse gases, ozone, and aerosols. The full-forcing runs provide a better match to observational changes in sea surface temperature in the vicinity of SWA. The observed rainfall decline is not well captured by rainfall changes simulated directly by the model in either ensemble. There is a hint that the fully forced ensemble is more realistic, but it is nothing more than a hint. The downscaling approach, on the other hand, provides a much more accurate reproduction of the day-to-day variability of rainfall in SWA than the rainfall simulated directly by the model. The downscaled ensemble mean rainfall in full forcing declines over the region with a spatial pattern that is similar to the observed decline. This contrasts with an increase of rainfall in the downscaled rainfall in the natural ensemble. These results give the clearest indication yet that anthropogenic forcing played a role in the drying of SWA. Note, however, that ambiguities remain. For example, although the observed decline fits within the range of downscaled model simulation, the ensemble mean rainfall decline is only about half of the observed estimate, the timing differs from the observations, drying did not occur in the downscaling of one of the four fall-forced ensemble members, and not all potential forcing mechanisms are included in full forcing (e.g., land surface changes). Furthermore, while the observed rainfall decline was a sharp reduction in the 1960s, followed by a near-constant rainfall regime, the full-forcing ensemble suggests a more gradual rainfall decline over 40 yr from 1960
Harvest disruption projections for the Australian sugar industry
No full textPurpose: To investigate the effects of climate change on harvestability for sugarcane-growing regions situated between mountain ranges and the narrow east Australian coastline.
Design/methodology/approach: Daily rainfall simulations from 11 general circulation models (GCMs) were downscaled for seven Australian sugarcane regions (1961:2000). Unharvestable days were calculated from these 11 GCMs and compared to interpolated observed data. The historical downscaled GCM simulations were then compared to simulations under a low (B1) and high (A2) emissions scenario for the period 2046:2065. The 25th, 50th and 75th percentiles of paired model differences were assessed using 95% bootstrapped confidence intervals.
Findings: A decrease in the number of unharvestable days for the Burdekin (winter /spring) and Bundaberg (winter) regions and an increase for the Herbert region (spring) were plausible under the A2 scenario. Variability between GCM projections was higher for some regions compared to others and was generally higher in spring than winter. Spatial plots identified variability within regions. Northern and southern regions were more variable than central regions.
Practical implications: Recent studies have projected increases in simulated yields under future climate conditions. Changes to the frequency of unharvestable days may require a range of management adaptations to deal with an increased harvest and an effectively shorter harvest window. Regions where an increase in unharvestable days is plausible may consider modifying the harvest period and upgrading harvesting technologies.
Originality/value: The application of a targeted industry rainfall parameter (unharvestable days) obtained from downscaled climate models provided a novel approach to investigate the impacts of climate change. This research forms a baseline for industry discussion and adaptation planning towards an environmentally and economically sustainable future. The methodology outlined can easily be extended to other primary industries impacted by wet weather
The role of East Coast Lows on rainfall patterns and inter‐annual variability across the East Coast of Australia
No full textLinear and nonlinear statistical analysis of the impact of sub-tropical ridge intensity and position on south-east Australian rainfall
No full textThe intensity and position of the sub-tropical ridge (STR) have strong relationships with rainfall variability in southern Australia. The combined effect of intensity and position in March-April-May (MAM) and June-July-August (JJA) is the focus of this research. Linear statistics were used first: area-averaged and Australia-wide spatial correlations of STR intensity and position with precipitation in south-west eastern Australia reveal that STR intensity has a much stronger and more widespread relationship with precipitation in both seasons. Over time, these relationships vary in magnitude and spatial extent with the sign of the correlation changing between two 50-year epochs. These nonlinearities were investigated further using classification trees. Area-averaged precipitation data (terciles) for south-west eastern Australia was classified on the basis of STR intensity and position. In both seasons the classification trees identify STR intensity as the primary partition defining the dry group, supporting the linear analysis. In the transition season of MAM, the time of year when the mean position of the STR is more southerly, STR position is important in distinguishing between a 'winter-like' and a 'summer-like' wet groups, providing STR intensity is low. Vector wind analyses were computed to explain the composite seasonal precipitation anomaly results in terms of different circulation patterns associated with these two wet groups. The frequency of wet and dry cases in each group was examined with changes evident over the recent years. The research confirms that STR intensity is more important than STR position in explaining inter-annual rainfall variability across southern Australia but also demonstrates the additional role of STR position in MAM. These results explain the low correlation between rainfall and STR position and why this relationship has evolved during the 20th century as the mean location of the STR has shifted south in MAM
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