Publications / Peer Reviewed Papers

Severe Convective Wind Environments and Future Projected Changes in Australia

Brown A and Dowdy A (2021) Severe Convective Wind Environments and Future Projected Changes in Australia. Journal of Geophysical Research: Atmospheres 126(16), e2021JD034633. https://doi.org/10.1029/2021JD034633

Thunderstorms can produce severe convective winds (SCWs) that damage buildings and other infrastructure such as electricity transmission towers. Understanding the climatology of SCWs is therefore important for planning and risk management. An archive of observed SCWs is used to examine a diverse set of diagnostics for indicating SCW environments based on reanalysis data. These diagnostics are then applied to climate model data to examine projections of future climate change for Australia. A diagnostic based on logistic regression is found to provide a better representation of observed SCW occurrences than other diagnostics. Projections for the future based on that diagnostic indicate increases and decreases between −16% and 34% in the occurrence frequency of regionally averaged SCW environments, based on the 10th and 90th percentile estimates of annual mean changes from a 12-member ensemble of global climate models. Projections based on other severe weather diagnostics indicate a wider range of future changes, including increases and decreases of up to 50% in magnitude, with regional and seasonal variations through Australia. Changes in the frequency of SCW environments appears to be largely driven by increased low level moisture concentrations which can lead to increased convective available potential energy, countered in some cases by a stabilization of the mid-troposphere temperature lapse rate. These results represent the most comprehensive estimate to date for constraining the range of uncertainty in projected future changes in convective environments for Australia, including severe thunderstorms and associated SCWs, noting that this has significant implications for risk management and climate adaptation purposes.

Publications / Peer Reviewed Papers

Severe convection-related winds in Australia and their associated environments.

Extremes Wind

Brown A and Dowdy A (2021) Severe convection-related winds in Australia and their associated environments. Journal of Southern Hemisphere Earth Systems Science 71, 30-52.

Severe surface wind gusts produced by thunderstorms have the potential to damage infrastructure and are a major hazard for society. Wind gust data are examined from 35 observing stations around Australia, with lightning observations used to indicate the occurrence of deep convective processes in the vicinity of the observed wind gusts. A collation of severe thunderstorm reports is also used to complement the station wind gust data. Atmospheric reanalysis data are used to systematically examine large-scale environmental measures associated with severe convective winds. We find that methods based on environmental measures provide a better indication of the observed severe convective winds than the simulated model wind gusts from the reanalysis data, noting that the spatial scales on which these events occur are typically smaller than the reanalysis grid cells. Consistent with previous studies in other regions and idealised modelling, the majority of severe convective wind events are found to occur in environments with steep mid-level tropospheric lapse rates, moderate convective instability and strong background wind speeds. A large proportion of events from measured station data occur with relatively dry environmental air at low levels, although it is unknown to what extent this type of environment is representative of other severe wind-producing convective modes in Australia. The occurrence of severe convective winds is found to be well represented by a number of indices used previously for forecasting applications, such as the weighted product of convective available potential energy (CAPE) and vertical wind shear, the derecho composite parameter and the total totals index, as well as by logistic regression methods applied to environmental variables. Based on the systematic approach used in this study, our findings provide new insight on spatio-temporal variations in the risk of damaging winds occurring, including the environmental factors associated with their occurrence.

Publications / Peer Reviewed Papers

Temperature impacts on utility-scale solar photovoltaic and wind power generation output over Australia under RCP 8.5

Temperature Solar-PV

Huang J, Jones B, Thatcher M, Landsberg J (2020) Temperature impacts on utility-scale solar photovoltaic and wind power generation output over Australia under RCP 8.5. Journal of Renewable and Sustainable Energy 12:046501

Climate change has the potential to impact the generation of renewable energy significantly subject to location and equipment specifications. As the penetration of renewable energy in the energy systems keeps increasing, this impact needs be systematically assessed so that investment and reliability information is accurate. Australia represents an ideal study case characterized by its frequency of extreme weather events and the recent and planned growth in the renewable energy sector. In this study, we model and quantify the long-term temperature de-rating impact of utility-scale solar photovoltaic and wind power generation over Australia. Using climate projections simulated by six Global Circulation Models and the CSIRO's Cubic Conformal Atmospheric Model, we analyze half-hourly time series of key weather variables such as temperature, surface solar irradiance, and wind speed for 1980–2060 at two sites where variable renewable generators are located, or are likely to be located in the future based on the current Integrated System Plan by the Australian Energy Market Operator. We also built power conversion models for the temperature de-rating of solar and wind power with added focus on high temperature scenarios. We found that the general temporal trends in annual solar and wind power generation due to climate change are small, being at the order of 0.1% of their average production per decade. However, for peak temperature events, which coincide with the peak power demand and, generally, high prices, the temperature de-rating impact can be much more substantial and disruptive.

Publications / Peer Reviewed Papers

Australian Rainfall Anomalies in 2018–2019 Linked to Indo-Pacific Driver Indices Using ERA5 Reanalyses

Rainfall Drivers

Watterson IG (2020) Australian Rainfall Anomalies in 2018–2019 Linked to Indo-Pacific Driver Indices Using ERA5 Reanalyses. Journal of Geophysical Research: Atmospheres 125:e2020JD033041

Abstract The 2019 and 2018–2019 periods had record low All-Australia rainfall in both observations and the ECMWF's Reanalysis 5, or ERA5, data set over 1979–2019. An analysis of the relationships between interannual variability of rainfall and atmospheric circulation, vertically integrated moisture flux, and temperature anomalies using ERA5 alone is undertaken. Both standard driver indices and those that combine the Pacific and Indian Ocean influences are used. Regression fields for low annual Australian rainfall show a widespread negative rainfall anomaly extending into the east Indian Ocean or IND region and a positive anomaly in the western Pacific PAC region. A moisture flux anomaly takes moisture eastwards toward PAC. This pattern largely persists in the four seasons. In March–May 2019 it can be partially linked to a positive Niño 3.4 anomaly and in June–August to a positive Indian Ocean Dipole. For the annual case, the detrended Niño 4 index explains 24% of the 2019 ERA5 Australian rainfall deficit. This rises to 38% for the 2018–2019 deficit (46% for observations), for the Pacific-Indian Dipole index that combines the PAC and IND regions, whose sea surface temperature anomalies have opposite effects. The correlation of the index with 2-year rainfall is −0.7. There is much variability, in the Australian monsoon rainfall especially, that is not linked to simple indices, although rainfall is well matched with moisture flux convergence. This extends to the equatorial zone where the climate of the Maritime Continent can be better examined with ERA5's 0.25° data.

Publications / Submitted Manuscripts

Towards ACCESS-based regional climate projections for Australia

Modelling Downscaling ACCESS

Su C-H, Ye H, Dowdy A, et al. (submitted). ‘Towards ACCESS-based regional climate projections for Australia’ Geoscientific Model Development (submitted February 2021).

Abstract