School of Earth Sciences - Research Publications

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    Forecasting wildlife die-offs from extreme heat events
    Ratnayake, HU ; Kearney, MR ; Govekar, P ; Karoly, D ; Welbergen, JA (WILEY, 2019-08)
    Abstract Extreme heat events pose increasing challenges to biodiversity conservation worldwide, yet our ability to predict the time, place and magnitude of their impacts on wildlife is limited. Extreme heat events in Australia are known to kill thousands of flying‐foxes (Pteropus spp.), and such die‐offs are expected to become more frequent and widespread in the future under anthropogenic climate change. There is a growing need for predicting when and where such heat‐related die‐offs would occur, to facilitate short‐term wildlife management and conservation actions. In this study, we used gridded hourly air temperature forecasts [Australian Community Climate and Earth‐System Simulator (ACCESS‐R) Numerical Weather Prediction (NWP) model] from the Australian Bureau of Meteorology to predict flying‐fox heat‐related mortality based on an empirically determined threshold of 42.0°C. We tested the accuracy and precision of this model using a twofold evaluation of the ACCESS‐R NWP forecast air temperature during a recorded extreme heat event with in situ air temperature measurements and interpolated weather station data. While our results showed a slight discrepancy between the modelled and measured air temperatures, there was no significant difference in the forecast's accuracy to predict die‐offs during an extreme heat event and the overall summer period. We evaluated the accuracy of mortality predictions based on different air temperature thresholds (38.0, 40.0, 42.0 and 44.0°C). Our results revealed a significant probability of flying‐fox mortality occurrence when forecast air temperature was ≥42.0°C, while the 24‐ and 48‐h forecasts accurately predicted 77 and 73% of the die‐offs, respectively. Thus, the use of 42.0°C forecast air temperature from the ACCESS‐R NWP model can predict flying‐fox mortality reliably at the landscape scale. In principle, the forecaster can be used for any species with known thermal tolerance data and is therefore a promising new tool for prioritizing adaptation actions that aim to conserve biodiversity in the face of climate change.
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    Geoengineering governance-by-default: an earth system governance perspective
    Talberg, A ; Christoff, P ; Thomas, S ; Karoly, D (SPRINGER, 2018-04)
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    How geoengineering scenarios frame assumptions and create expectations
    Talberg, A ; Thomas, S ; Christoff, P ; Karoly, D (SPRINGER JAPAN KK, 2018-07)
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    A regionalisation approach for rainfall based on extremal dependence
    Saunders, KR ; Stephenson, AG ; Karoly, DJ (SPRINGER, 2021-06)
    Abstract To mitigate the risk posed by extreme rainfall events, we require statistical models that reliably capture extremes in continuous space with dependence. However, assuming a stationary dependence structure in such models is often erroneous, particularly over large geographical domains. Furthermore, there are limitations on the ability to fit existing models, such as max-stable processes, to a large number of locations. To address these modelling challenges, we present a regionalisation method that partitions stations into regions of similar extremal dependence using clustering. To demonstrate our regionalisation approach, we consider a study region of Australia and discuss the results with respect to known climate and topographic features. To visualise and evaluate the effectiveness of the partitioning, we fit max-stable models to each of the regions. This work serves as a prelude to how one might consider undertaking a project where spatial dependence is non-stationary and is modelled on a large geographical scale.
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    Warming Patterns Affect El Nino Diversity in CMIP5 and CMIP6 Models
    Freund, MB ; Brown, JR ; Henley, BJ ; Karoly, DJ ; Brown, JN (American Meteorological Society, 2020-10-01)
    Given the consequences and global significance of El Niño–Southern Oscillation (ENSO) events it is essential to understand the representation of El Niño diversity in climate models for the present day and the future. In recent decades, El Niño events have occurred more frequently in the central Pacific (CP). Eastern Pacific (EP) El Niño events have increased in intensity. However, the processes and future implications of these observed changes in El Niño are not well understood. Here, the frequency and intensity of El Niño events are assessed in models from phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6), and results are compared to extended instrumental and multicentury paleoclimate records. Future changes of El Niño are stronger for CP events than for EP events and differ between models. Models with a projected La Niña–like mean-state warming pattern show a tendency toward more EP but fewer CP events compared to models with an El Niño–like warming pattern. Among the models with more El Niño–like warming, differences in future El Niño can be partially explained by Pacific decadal variability (PDV). During positive PDV phases, more El Niño events occur, so future frequency changes are mainly determined by projected changes during positive PDV phases. Similarly, the intensity of El Niño is strongest during positive PDV phases. Future changes to El Niño may thus depend on both mean-state warming and decadal-scale natural variability.
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    Evaluation of CMIP6 AMIP climate simulations with the ACCESS-AM2 model
    Bodman, RW ; Karoly, DJ ; Dix, MR ; Harman, IN ; Srbinovsky, J ; Dobrohotoff, PB ; Mackallah, C (CSIRO PUBLISHING, 2020)
    The most recent version of the ACCESS-AM2 atmosphere-only climate model is introduced with results from the CMIP6 Atmospheric Model Intercomparison Project (AMIP) experiments configured with two land-surface models: CABLE and JULES. AMIP simulations are required as part of the CMIP6 core experiments. They are forced by prescribed time-varying observed sea surface temperature and sea-ice variations as well as variations in natural and anthropogenic external forcings. We evaluate the performance of the two configurations using three historical realisations for each. Model biases are estimated both globally and for the Australian region. The model shows close agreement with observed interannual variations of global-mean temperature across the latitude range 65°N–65°S. This is also true for the land-only temperature for 65°N–65°S, and a more stringent test of the model is driven by specified observed sea surface temperatures. Patterns of mean precipitation are simulated reasonably well, although there are biases in the amount and distribution of precipitation, typical of longstanding problems in representing this aspect of the climate. Selected features of the atmospheric circulation are discussed, including air temperatures and wind speeds. For the Australian region, in addition to examining the climatological patterns of temperature and precipitation, important drivers of climate variability are reviewed: El Niño-Southern Oscillation, the Indian Ocean Dipole and the Southern Annular Mode. In general, the correlation patterns for precipitation simulated by ACCESS-AM2 are somewhat weaker than in observations, although the ensemble means show better agreement than individual ensemble members. Overall, the two different land-surface schemes perform similarly. ACCESS-AM2 has reduced root mean square errors for both temperature and precipitation of around 15–20% at the global scale compared to the older CMIP5 versions of the model: ACCESS 1.0 and ACCESS 1.3.
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    The Role of Health Co-Benefits in the Development of Australian Climate Change Mitigation Policies
    Workman, A ; Blashki, G ; Karoly, D ; Wiseman, J (MDPI, 2016-09)
    Reducing domestic carbon dioxide and other associated emissions can lead to short-term, localized health benefits. Quantifying and incorporating these health co-benefits into the development of national climate change mitigation policies may facilitate the adoption of stronger policies. There is, however, a dearth of research exploring the role of health co-benefits on the development of such policies. To address this knowledge gap, research was conducted in Australia involving the analysis of several data sources, including interviews carried out with Australian federal government employees directly involved in the development of mitigation policies. The resulting case study determined that, in Australia, health co-benefits play a minimal role in the development of climate change mitigation policies. Several factors influence the extent to which health co-benefits inform the development of mitigation policies. Understanding these factors may help to increase the political utility of future health co-benefits studies.
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    Higher frequency of Central Pacific El Nino events in recent decades relative to past centuries
    Freund, MB ; Henley, BJ ; Karoly, DJ ; McGregor, HV ; Abram, NJ ; Dommenget, D (NATURE PUBLISHING GROUP, 2019-06-01)
    El Niño events differ substantially in their spatial pattern and intensity. Canonical Eastern Pacific El Niño events have sea surface temperature anomalies that are strongest in the far eastern equatorial Pacific, whereas peak ocean warming occurs further west during Central Pacific El Niño events. The event types differ in their impacts on the location and intensity of temperature and precipitation anomalies globally. Evidence is emerging that Central Pacific El Niño events have become more common, a trend that is projected by some studies to continue with ongoing climate change. Here we identify spatial and temporal patterns in observed sea surface temperatures that distinguish the evolution of Eastern and Central Pacific El Niño events in the tropical Pacific. We show that these patterns are recorded by a network of 27 seasonally resolved coral records, which we then use to reconstruct Central and Eastern Pacific El Niño activity for the past four centuries. We find a simultaneous increase in Central Pacific events and a decrease in Eastern Pacific events since the late twentieth century that leads to a ratio of Central to Eastern Pacific events that is unusual in a multicentury context. Compared to the past four centuries, the most recent 30 year period includes fewer, but more intense, Eastern Pacific El Niño events.
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    Seasonal dependence of rainfall extremes in and around Jakarta, Indonesia
    Lestari, S ; King, A ; Vincent, C ; Karoly, D ; Protat, A (Elsevier, 2019)
    This study investigates the interannual, seasonal, and intraseasonal variation in rainfall extremes (REs) in Jakarta and surroundings. We used datasets of daily rainfall at three sites at coastal, inland and mountainous environments during 1974–2016 (42 years), Sea Surface Temperature, 850-hPa zonal and meridional winds, and Outgoing Longwave Radiation during 1979–2016 (37 years). The results show that intensity and frequency of REs, and their relative contribution to the total rainfall, have strong relationships with the Indian Ocean Dipole and El Niño Southern Oscillation in the dry season (Jun–Nov) but weak relationships in the wet season (Dec–May) at all sites. During active Madden-Julian Oscillation (MJO) period, the daily average rainfall and the number of RE days relative to all days show strong variation between MJO phases at all sites and the MJO signature differs between the three stations. At the coastal and inland sites, there is a less marked variation of the number of RE events relative to all days with MJO phases. Compared to lower altitudes, the high-altitude station has a greater number of RE events relative to all days in the wet season and a lower intensity of REs relative to total rainfall amount in the dry season. The results of the study suggest that the REs vary in each station due to highly localised differences in responses to large-scale conditions.
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    Amplification of risks to water supply at 1.5°C and 2°C in drying climates: a case study for Melbourne, Australia
    Henley, BJ ; Peel, MC ; Nathan, R ; King, AD ; Ukkola, AM ; Karoly, DJ ; Tan, KS (IOP Publishing, 2019-08-02)
    Human-induced climate change poses a major threat to the reliable water supply in many highly populated regions. Here we combine hydrological and climate model simulations to evaluate risks to the water supply under projected shifts in the climate at the Paris Agreement warming levels. Modelling the primary surface water sources for Melbourne, Australia, we project that the risk of severe water supply shortage to the climate-dependent portion of the system increases substantially as global warming increases from 1.5 °Cto 2.0 °C. Risks are further exacerbated by increases in water demand but substantially ameliorated by supply augmentation from desalination.Wedemonstrate that reductions in precipitation, rising temperature and growth in water demand combine to substantially amplify the risk of severe water supply shortage under near-term global warming in the absence of a climate-independent supply. This risk amplification is not as apparent in assessments based on meteorological drought alone. With the diminishing opportunity of meeting the 1.5 °CParis target, our study highlights the need to accelerate greenhouse gas mitigation efforts to reduce risks to climate dependent water supply systems.