Decreasing global tropical cyclone frequency in CMIP6 historical simulations
- Zhao, Haikun, Zhao, Kai, Klotzbach, Philip, Chand, Savin, Camargo, Suzana, Cao, Jian, Wu, Liguang
- Authors: Zhao, Haikun , Zhao, Kai , Klotzbach, Philip , Chand, Savin , Camargo, Suzana , Cao, Jian , Wu, Liguang
- Date: 2024
- Type: Text , Journal article
- Relation: Science Advances Vol. 10, no. 27 (2024), p.
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- Description: The impact of anthropogenic global warming on tropical cyclone (TC) frequency remains a challenging issue, partly due to a relatively short period of reliable observational TC records and inconsistencies in climate model simulations. Using TC detection from 20 CMIP6 historical simulations, we show that the majority (75%) of these models show a decrease in global-scale TC frequency from 1850 to 2014. We demonstrated that this result is largely explained by weakened mid-tropospheric upward motion in CMIP6 models over the Pacific and Atlantic main development regions. The reduced upward motion is due to a zonal circulation adjustment and shifts in Intertropical Convergence Zone in response to global warming. In the South Indian Ocean, reduced TC frequency is mainly due to the decreased survival rate of TC seeds because of an increased saturation deficit in a warming climate. Our analysis highlights global warming's potential impact on the historical decrease in global TC frequency. © 2024 The Authors.
- Authors: Zhao, Haikun , Zhao, Kai , Klotzbach, Philip , Chand, Savin , Camargo, Suzana , Cao, Jian , Wu, Liguang
- Date: 2024
- Type: Text , Journal article
- Relation: Science Advances Vol. 10, no. 27 (2024), p.
- Full Text:
- Reviewed:
- Description: The impact of anthropogenic global warming on tropical cyclone (TC) frequency remains a challenging issue, partly due to a relatively short period of reliable observational TC records and inconsistencies in climate model simulations. Using TC detection from 20 CMIP6 historical simulations, we show that the majority (75%) of these models show a decrease in global-scale TC frequency from 1850 to 2014. We demonstrated that this result is largely explained by weakened mid-tropospheric upward motion in CMIP6 models over the Pacific and Atlantic main development regions. The reduced upward motion is due to a zonal circulation adjustment and shifts in Intertropical Convergence Zone in response to global warming. In the South Indian Ocean, reduced TC frequency is mainly due to the decreased survival rate of TC seeds because of an increased saturation deficit in a warming climate. Our analysis highlights global warming's potential impact on the historical decrease in global TC frequency. © 2024 The Authors.
Occurrence and trends of historical tropical cyclone rainfall on near-coastal regions of Australia
- Bell, Samuel, Dowdy, Andrew, Chand, Savin, Su, Chun-Hsu
- Authors: Bell, Samuel , Dowdy, Andrew , Chand, Savin , Su, Chun-Hsu
- Date: 2024
- Type: Text , Journal article
- Relation: Journal of Southern Hemisphere Earth Systems Science Vol. 74, no. 2 (2024), p.
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- Description: Extreme rainfall driven by tropical cyclones (TCs) has profound effects on Australian coastlines at both local and regional scales. Here, we develop methods for comparing TC-driven widespread and localised rainfall on three broad coastal regions of tropical Australia (west, north and east). Trends, average recurrence intervals (ARIs) and the fractional contribution of TC rainfall are explored in three historical datasets: Australian Gridded Climate Data (AGCD), ECMWF Reanalysis (ver. 5, ERA5) and the Bureau of Meteorology Atmospheric high resolution Regional Reanalysis for Australia (ver. 1, BARRA1). Results for trends and ARIs between the different datasets are generally inconsistent and also differ between regions, partially owing to the short-term temporal records of some of the data as well as inconsistencies in extreme values between datasets. By contrast, there is a general agreement between all datasets on the fractional contribution of TC rainfall, signalling an increase in recent years. This result is considered together with the trend towards fewer TCs occurring in this region over recent decades, indicating a trend towards increased rainfall intensity per TC on average, assuming steady landfall rates. The methods developed here can be applied easily to other data types such as regional climate model experiments, facilitating a multiple lines of evidence approach that incorporates both observational-based and model-based data. This research is intended to help provide new methods and guidance for identifying trends in TC-driven extreme rainfall, relevant for enhanced planning and adaptation to the impacts of these extreme weather systems. © 2024 The Author(s)
- Authors: Bell, Samuel , Dowdy, Andrew , Chand, Savin , Su, Chun-Hsu
- Date: 2024
- Type: Text , Journal article
- Relation: Journal of Southern Hemisphere Earth Systems Science Vol. 74, no. 2 (2024), p.
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- Description: Extreme rainfall driven by tropical cyclones (TCs) has profound effects on Australian coastlines at both local and regional scales. Here, we develop methods for comparing TC-driven widespread and localised rainfall on three broad coastal regions of tropical Australia (west, north and east). Trends, average recurrence intervals (ARIs) and the fractional contribution of TC rainfall are explored in three historical datasets: Australian Gridded Climate Data (AGCD), ECMWF Reanalysis (ver. 5, ERA5) and the Bureau of Meteorology Atmospheric high resolution Regional Reanalysis for Australia (ver. 1, BARRA1). Results for trends and ARIs between the different datasets are generally inconsistent and also differ between regions, partially owing to the short-term temporal records of some of the data as well as inconsistencies in extreme values between datasets. By contrast, there is a general agreement between all datasets on the fractional contribution of TC rainfall, signalling an increase in recent years. This result is considered together with the trend towards fewer TCs occurring in this region over recent decades, indicating a trend towards increased rainfall intensity per TC on average, assuming steady landfall rates. The methods developed here can be applied easily to other data types such as regional climate model experiments, facilitating a multiple lines of evidence approach that incorporates both observational-based and model-based data. This research is intended to help provide new methods and guidance for identifying trends in TC-driven extreme rainfall, relevant for enhanced planning and adaptation to the impacts of these extreme weather systems. © 2024 The Author(s)
An update on the influence of natural climate variability and anthropogenic climate change on tropical cyclones
- Camargo, Suzana, Murakami, Hiroyuki, Bloemendaal, Nadia, Chand, Savin, Deshpande, Medha, Dominguez-Sarmiento, Christian, González-Alemán, Juan, Knutson, Thomas, Lin, I., Moon, Il-Ju, Patricola, Christian, Reed, Kevin, Roberts, Malcolm, Scoccimarro, Enrico, Tam, Chi, Wallace, Elizabeth, Wu, Liguang, Yamada, Yohei, Zhang, Wei, Zhao, Haikun
- Authors: Camargo, Suzana , Murakami, Hiroyuki , Bloemendaal, Nadia , Chand, Savin , Deshpande, Medha , Dominguez-Sarmiento, Christian , González-Alemán, Juan , Knutson, Thomas , Lin, I. , Moon, Il-Ju , Patricola, Christian , Reed, Kevin , Roberts, Malcolm , Scoccimarro, Enrico , Tam, Chi , Wallace, Elizabeth , Wu, Liguang , Yamada, Yohei , Zhang, Wei , Zhao, Haikun
- Date: 2023
- Type: Text , Journal article
- Relation: Tropical Cyclone Research and Review Vol. 12, no. 3 (2023), p. 216-239
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- Description: A substantial number of studies have been published since the Ninth International Workshop on Tropical Cyclones (IWTC-9) in 2018, improving our understanding of the effect of climate change on tropical cyclones (TCs) and associated hazards and risks. These studies have reinforced the robustness of increases in TC intensity and associated TC hazards and risks due to anthropogenic climate change. New modeling and observational studies suggested the potential influence of anthropogenic climate forcings, including greenhouse gases and aerosols, on global and regional TC activity at the decadal and century time scales. However, there are still substantial uncertainties owing to model uncertainty in simulating historical TC decadal variability in the Atlantic, and the limitations of observed TC records. The projected future change in the global number of TCs has become more uncertain since IWTC-9 due to projected increases in TC frequency by a few climate models. A new paradigm, TC seeds, has been proposed, and there is currently a debate on whether seeds can help explain the physical mechanism behind the projected changes in global TC frequency. New studies also highlighted the importance of large-scale environmental fields on TC activity, such as snow cover and air-sea interactions. Future projections on TC translation speed and medicanes are new additional focus topics in our report. Recommendations and future research are proposed relevant to the remaining scientific questions and assisting policymakers. © 2023 The Shanghai Typhoon Institute of China Meteorological Administration
- Authors: Camargo, Suzana , Murakami, Hiroyuki , Bloemendaal, Nadia , Chand, Savin , Deshpande, Medha , Dominguez-Sarmiento, Christian , González-Alemán, Juan , Knutson, Thomas , Lin, I. , Moon, Il-Ju , Patricola, Christian , Reed, Kevin , Roberts, Malcolm , Scoccimarro, Enrico , Tam, Chi , Wallace, Elizabeth , Wu, Liguang , Yamada, Yohei , Zhang, Wei , Zhao, Haikun
- Date: 2023
- Type: Text , Journal article
- Relation: Tropical Cyclone Research and Review Vol. 12, no. 3 (2023), p. 216-239
- Full Text:
- Reviewed:
- Description: A substantial number of studies have been published since the Ninth International Workshop on Tropical Cyclones (IWTC-9) in 2018, improving our understanding of the effect of climate change on tropical cyclones (TCs) and associated hazards and risks. These studies have reinforced the robustness of increases in TC intensity and associated TC hazards and risks due to anthropogenic climate change. New modeling and observational studies suggested the potential influence of anthropogenic climate forcings, including greenhouse gases and aerosols, on global and regional TC activity at the decadal and century time scales. However, there are still substantial uncertainties owing to model uncertainty in simulating historical TC decadal variability in the Atlantic, and the limitations of observed TC records. The projected future change in the global number of TCs has become more uncertain since IWTC-9 due to projected increases in TC frequency by a few climate models. A new paradigm, TC seeds, has been proposed, and there is currently a debate on whether seeds can help explain the physical mechanism behind the projected changes in global TC frequency. New studies also highlighted the importance of large-scale environmental fields on TC activity, such as snow cover and air-sea interactions. Future projections on TC translation speed and medicanes are new additional focus topics in our report. Recommendations and future research are proposed relevant to the remaining scientific questions and assisting policymakers. © 2023 The Shanghai Typhoon Institute of China Meteorological Administration
Clustering tropical cyclone genesis on ENSO timescales in the southwest Pacific
- Tu’uholoaki, Moleni, Espejo, Antonio, Singh, Awnesh, Damlamian, Herve, Wandres, Moritz, Chand, Savin, Mendez, Fernando, Fa’anunu, Ofa
- Authors: Tu’uholoaki, Moleni , Espejo, Antonio , Singh, Awnesh , Damlamian, Herve , Wandres, Moritz , Chand, Savin , Mendez, Fernando , Fa’anunu, Ofa
- Date: 2023
- Type: Text , Journal article
- Relation: Climate Dynamics Vol. 60, no. 11-12 (2023), p. 3353-3368
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- Description: Tropical cyclones (TCs) as a natural hazard pose a major threat and risk to the human population globally. This threat is expected to increase in a warming climate as the frequency of severe TCs is expected to increase. In this study, the influence of different monthly sea surface temperature (SST) patterns on the locations and frequency of tropical cyclone genesis (TCG) in the Southwest Pacific (SWP) region is investigated. Using principal component analysis and k-means clustering of monthly SST between 1970 and 2019, nine statistically different SST patterns are identified. Our findings show that the more prominent ENSO patterns such as the Modoki El Niño (i.e., Modoki I and Modoki II) and Eastern Pacific (EP) El Niño impact the frequency and location of TCG significantly. Our results enhance the overall understanding of the TCG variability and the relationship between TCG and SST configurations in the SWP region. The results of this study may support early warning system in SWP by improving seasonal outlooks and quantification of the level of TC-related risks for the vulnerable Pacific Island communities. © 2022, The Author(s).
- Authors: Tu’uholoaki, Moleni , Espejo, Antonio , Singh, Awnesh , Damlamian, Herve , Wandres, Moritz , Chand, Savin , Mendez, Fernando , Fa’anunu, Ofa
- Date: 2023
- Type: Text , Journal article
- Relation: Climate Dynamics Vol. 60, no. 11-12 (2023), p. 3353-3368
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- Description: Tropical cyclones (TCs) as a natural hazard pose a major threat and risk to the human population globally. This threat is expected to increase in a warming climate as the frequency of severe TCs is expected to increase. In this study, the influence of different monthly sea surface temperature (SST) patterns on the locations and frequency of tropical cyclone genesis (TCG) in the Southwest Pacific (SWP) region is investigated. Using principal component analysis and k-means clustering of monthly SST between 1970 and 2019, nine statistically different SST patterns are identified. Our findings show that the more prominent ENSO patterns such as the Modoki El Niño (i.e., Modoki I and Modoki II) and Eastern Pacific (EP) El Niño impact the frequency and location of TCG significantly. Our results enhance the overall understanding of the TCG variability and the relationship between TCG and SST configurations in the SWP region. The results of this study may support early warning system in SWP by improving seasonal outlooks and quantification of the level of TC-related risks for the vulnerable Pacific Island communities. © 2022, The Author(s).
Influence of the Madden–Julian Oscillation (MJO) on tropical cyclones affecting Tonga in the Southwest Pacific
- Tu’uholoaki, Moleni, Espejo, Antonio, Sharma, Krishneel, Singh, Awnesh, Wandres, Moritz, Damlamian, Herve, Chand, Savin
- Authors: Tu’uholoaki, Moleni , Espejo, Antonio , Sharma, Krishneel , Singh, Awnesh , Wandres, Moritz , Damlamian, Herve , Chand, Savin
- Date: 2023
- Type: Text , Journal article
- Relation: Atmosphere Vol. 14, no. 7 (2023), p.
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- Description: The modulating influence of the Madden–Julian oscillation (MJO) on tropical cyclones (TCs) has been examined globally, regionally, and subregionally, but its impact on the island scale remains unclear. This study investigates how TC activity affecting the Tonga region is being modulated by the MJO, using the Southwest Pacific Enhanced Archive of Tropical Cyclones (SPEArTC) and the MJO index. In particular, this study investigates how the MJO modulates the frequency and intensity of TCs affecting the Tonga region relative to the entire study period (1970–2019; hereafter referred to as all years), as well as to different phases of the El Niño southern oscillation (ENSO) phenomenon. Results suggest that the MJO strongly modulates TC activity affecting the Tonga region. The frequency and intensity of TCs is enhanced during the active phases (phases six to eight) in all years, including El Niño and ENSO-neutral years. The MJO also strongly influences the climatological pattern of genesis of TCs affecting the Tonga region, where more (fewer) cyclones form in the active (inactive) phases of the MJO and more genesis points are clustered (scattered) near (away from) the Tonga region. There were three regression curves that best described the movement of TCs in the region matching the dominant steering mechanisms in the Southwest Pacific region. The findings of this study can provide climatological information for the Tonga Meteorological Service (TMS) and disaster managers to better understand the TC risk associated with the impact of the MJO on TCs affecting the Tonga region and support its TC early warning system. © 2023 by the authors.
- Authors: Tu’uholoaki, Moleni , Espejo, Antonio , Sharma, Krishneel , Singh, Awnesh , Wandres, Moritz , Damlamian, Herve , Chand, Savin
- Date: 2023
- Type: Text , Journal article
- Relation: Atmosphere Vol. 14, no. 7 (2023), p.
- Full Text:
- Reviewed:
- Description: The modulating influence of the Madden–Julian oscillation (MJO) on tropical cyclones (TCs) has been examined globally, regionally, and subregionally, but its impact on the island scale remains unclear. This study investigates how TC activity affecting the Tonga region is being modulated by the MJO, using the Southwest Pacific Enhanced Archive of Tropical Cyclones (SPEArTC) and the MJO index. In particular, this study investigates how the MJO modulates the frequency and intensity of TCs affecting the Tonga region relative to the entire study period (1970–2019; hereafter referred to as all years), as well as to different phases of the El Niño southern oscillation (ENSO) phenomenon. Results suggest that the MJO strongly modulates TC activity affecting the Tonga region. The frequency and intensity of TCs is enhanced during the active phases (phases six to eight) in all years, including El Niño and ENSO-neutral years. The MJO also strongly influences the climatological pattern of genesis of TCs affecting the Tonga region, where more (fewer) cyclones form in the active (inactive) phases of the MJO and more genesis points are clustered (scattered) near (away from) the Tonga region. There were three regression curves that best described the movement of TCs in the region matching the dominant steering mechanisms in the Southwest Pacific region. The findings of this study can provide climatological information for the Tonga Meteorological Service (TMS) and disaster managers to better understand the TC risk associated with the impact of the MJO on TCs affecting the Tonga region and support its TC early warning system. © 2023 by the authors.
Reconstruction of tropical cyclone and depression proxies for the South Pacific since the 1850s
- Yeasmin, Alea, Chand, Savin, Sultanova, Nargiz
- Authors: Yeasmin, Alea , Chand, Savin , Sultanova, Nargiz
- Date: 2023
- Type: Text , Journal article
- Relation: Weather and Climate Extremes Vol. 39, no. (2023), p.
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- Description: Southwest Pacific nations are highly vulnerable to extreme weather and climate events, particularly those associated with synoptic-scale systems such as tropical cyclones (TCs) and depressions (TDs). This study utilises the Okubo–Weiss–Zeta parameter (OWZP) method to reconstruct historical records of both TCs and TDs for the South Pacific basin using state-of-the-art NOAA-CIRES Twentieth Century Reanalysis (20CR) product. Extensive statistical assessments of these reconstructions are carried out using observational records for the satellite period (i.e., 1979–2014) as ‘ground-truths’. Results show that 20CR-derived TCs and TDs resemble several key characteristics of the observational records, including spatial distribution of genesis locations and track shapes. This gives us confidence that the 20CR-derived long-term records of TCs and TDs can serve as an effective tool for examining historical changes in various characteristics of TCs and TDs, particularly in the context of anthropogenic climate change. © 2022
- Authors: Yeasmin, Alea , Chand, Savin , Sultanova, Nargiz
- Date: 2023
- Type: Text , Journal article
- Relation: Weather and Climate Extremes Vol. 39, no. (2023), p.
- Full Text:
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- Description: Southwest Pacific nations are highly vulnerable to extreme weather and climate events, particularly those associated with synoptic-scale systems such as tropical cyclones (TCs) and depressions (TDs). This study utilises the Okubo–Weiss–Zeta parameter (OWZP) method to reconstruct historical records of both TCs and TDs for the South Pacific basin using state-of-the-art NOAA-CIRES Twentieth Century Reanalysis (20CR) product. Extensive statistical assessments of these reconstructions are carried out using observational records for the satellite period (i.e., 1979–2014) as ‘ground-truths’. Results show that 20CR-derived TCs and TDs resemble several key characteristics of the observational records, including spatial distribution of genesis locations and track shapes. This gives us confidence that the 20CR-derived long-term records of TCs and TDs can serve as an effective tool for examining historical changes in various characteristics of TCs and TDs, particularly in the context of anthropogenic climate change. © 2022
Subseasonal prediction framework for tropical cyclone activity in the Solomon Islands region
- Haruhiru, Alick, Chand, Savin, Sultanova, Nargiz, Ramsay, Hamish, Sharma, Krishneel, Tahani, Lloyd
- Authors: Haruhiru, Alick , Chand, Savin , Sultanova, Nargiz , Ramsay, Hamish , Sharma, Krishneel , Tahani, Lloyd
- Date: 2023
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 43, no. 12 (2023), p. 5763-5777
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- Description: Recently, we developed seasonal prediction schemes with improved skill to predict tropical cyclone (TC) activity up to 3 months in advance for the Solomon Islands (SI) region (5°–15°S, 155°–170°E) using sophisticated Bayesian regression techniques. However, TC prediction at subseasonal timescale (i.e., 1–4 weeks in advance) is not being researched for that region despite growing demands from decision makers at sectoral level. In this paper, we first assess the feasibility of developing subseasonal prediction frameworks for the SI region using a pool of predictors that are known to affect TC activity in the region. We then evaluate multiple predictor combinations to develop the most appropriate models using a statistical approach to forecast weekly TC activity up to 4 weeks in advance. Predictors used include indices of various natural climate variability modes, namely the Madden–Julian Oscillation (MJO), the El Niño–Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the Interdecadal Pacific Oscillation (IPO). These modes often have robust physical and statistical relationships with TC occurrences in the SI region and the broader southwest Pacific territory as shown by preceding studies. Additionally, we incorporate TC seasonality as a potential predictor given the persistence of TCs occurring more in certain months than others. Note that a model with seasonality predictor alone (hereafter called the “climatology” model) forms a baseline for comparisons. The hindcast verifications of the forecasts using leave-one-out cross-validation procedure over the study period 1975–2019 indicate considerable improvements in prediction skill of our logistic regression models over climatology, even up to 4 weeks in advance. This study sets the foundation for introducing subseasonal prediction services, which is a national priority for improved decision making in sectors like agriculture and food security, water, health and disaster risk mitigation in the Solomon Islands. © 2023 The Authors. International Journal of Climatology published by John Wiley & Sons Ltd on behalf of Royal Meteorological Society.
- Authors: Haruhiru, Alick , Chand, Savin , Sultanova, Nargiz , Ramsay, Hamish , Sharma, Krishneel , Tahani, Lloyd
- Date: 2023
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 43, no. 12 (2023), p. 5763-5777
- Full Text:
- Reviewed:
- Description: Recently, we developed seasonal prediction schemes with improved skill to predict tropical cyclone (TC) activity up to 3 months in advance for the Solomon Islands (SI) region (5°–15°S, 155°–170°E) using sophisticated Bayesian regression techniques. However, TC prediction at subseasonal timescale (i.e., 1–4 weeks in advance) is not being researched for that region despite growing demands from decision makers at sectoral level. In this paper, we first assess the feasibility of developing subseasonal prediction frameworks for the SI region using a pool of predictors that are known to affect TC activity in the region. We then evaluate multiple predictor combinations to develop the most appropriate models using a statistical approach to forecast weekly TC activity up to 4 weeks in advance. Predictors used include indices of various natural climate variability modes, namely the Madden–Julian Oscillation (MJO), the El Niño–Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD) and the Interdecadal Pacific Oscillation (IPO). These modes often have robust physical and statistical relationships with TC occurrences in the SI region and the broader southwest Pacific territory as shown by preceding studies. Additionally, we incorporate TC seasonality as a potential predictor given the persistence of TCs occurring more in certain months than others. Note that a model with seasonality predictor alone (hereafter called the “climatology” model) forms a baseline for comparisons. The hindcast verifications of the forecasts using leave-one-out cross-validation procedure over the study period 1975–2019 indicate considerable improvements in prediction skill of our logistic regression models over climatology, even up to 4 weeks in advance. This study sets the foundation for introducing subseasonal prediction services, which is a national priority for improved decision making in sectors like agriculture and food security, water, health and disaster risk mitigation in the Solomon Islands. © 2023 The Authors. International Journal of Climatology published by John Wiley & Sons Ltd on behalf of Royal Meteorological Society.
Tropical cyclone activity in the Solomon Islands region : climatology, variability, and trends
- Haruhiru, Alick, Chand, Savin, Turville, Christopher, Ramsay, Hamish
- Authors: Haruhiru, Alick , Chand, Savin , Turville, Christopher , Ramsay, Hamish
- Date: 2023
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 43, no. 1 (2023), p. 593-614
- Full Text:
- Reviewed:
- Description: This study examines the climatology, variability, and trends of tropical cyclones (TCs) affecting the Solomon Islands (SI) territory, in the wider southwest Pacific (SWP), using the South Pacific Enhanced Archive for Tropical Cyclones (SPEArTC) database. During the period 1969/1970–2018/2019, 168 TCs were recorded in the SI territory. A cluster analysis is used to objectively partition these tracks into three clusters of similar TC trajectories to obtain better insights into the effects of natural climate variability, particularly due to the El Niño–Southern Oscillation (ENSO) phenomenon, which otherwise is not very apparent for TCs when considered collectively in the SI region. We find that TCs in clusters 1 and 3 show enhanced activity during El Niño phase, whereas TCs in cluster 2 are enhanced during La Niña and neutral phases. In addition to being modulated by ENSO, TCs in clusters 2 and 3 show statistically significant modulation at an intraseasonal timescale due to the Madden–Julian Oscillation (MJO) phenomenon. There are also some indications through sophisticated Bayesian modelling that TCs in clusters 2 and 3 are slightly influenced by the Interdecadal Pacific Oscillation (IPO). These results can have substantial implications for cluster-specific development of TC prediction schemes for the SI region. © 2022 The Authors. International Journal of Climatology published by John Wiley & Sons Ltd on behalf of Royal Meteorological Society.
- Authors: Haruhiru, Alick , Chand, Savin , Turville, Christopher , Ramsay, Hamish
- Date: 2023
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 43, no. 1 (2023), p. 593-614
- Full Text:
- Reviewed:
- Description: This study examines the climatology, variability, and trends of tropical cyclones (TCs) affecting the Solomon Islands (SI) territory, in the wider southwest Pacific (SWP), using the South Pacific Enhanced Archive for Tropical Cyclones (SPEArTC) database. During the period 1969/1970–2018/2019, 168 TCs were recorded in the SI territory. A cluster analysis is used to objectively partition these tracks into three clusters of similar TC trajectories to obtain better insights into the effects of natural climate variability, particularly due to the El Niño–Southern Oscillation (ENSO) phenomenon, which otherwise is not very apparent for TCs when considered collectively in the SI region. We find that TCs in clusters 1 and 3 show enhanced activity during El Niño phase, whereas TCs in cluster 2 are enhanced during La Niña and neutral phases. In addition to being modulated by ENSO, TCs in clusters 2 and 3 show statistically significant modulation at an intraseasonal timescale due to the Madden–Julian Oscillation (MJO) phenomenon. There are also some indications through sophisticated Bayesian modelling that TCs in clusters 2 and 3 are slightly influenced by the Interdecadal Pacific Oscillation (IPO). These results can have substantial implications for cluster-specific development of TC prediction schemes for the SI region. © 2022 The Authors. International Journal of Climatology published by John Wiley & Sons Ltd on behalf of Royal Meteorological Society.
Tropical cyclones and depressions over the South Pacific Ocean since the late 19th century : assessing synergistic relationship between the El Niño Southern Oscillation and Interdecadal Pacific Oscillation
- Yeasmin, Alea, Chand, Savin, Sultanova, Nargiz
- Authors: Yeasmin, Alea , Chand, Savin , Sultanova, Nargiz
- Date: 2023
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 43, no. 12 (2023), p. 5422-5443
- Full Text:
- Reviewed:
- Description: Tropical cyclones (TCs) and tropical depressions (TDs), hereafter collectively referred to as tropical storms, often exhibit large year-to-year variability in the South Pacific Ocean basin. Many past studies have examined this variability in relation to the El Niño Southern Oscillation (ENSO) phenomenon, particularly using observational data from the post-satellite era (i.e., after the 1970s when TC observations became more consistent). However, less emphasis is placed on how tropical storms are modulated at interdecadal and decadal time scales such as due to Interdecadal Pacific Oscillation (IPO). This is because post-satellite data are available for relatively short time period (i.e., post-1970s), limiting our understanding of the IPO–TC relationship in the South Pacific. Here, using NOAA-CIRES 20th Century Reanalysis (20CR) dataset, we reconstruct historical records (1871–2014) of TC and depression proxies for the South Pacific Ocean basin, and then utilize these reconstructed proxies to first understand the connections between TC–ENSO and TC–IPO over the 20th century, and then investigate the combined effects of ENSO–IPO effects on TCs and depressions. Results show that La Niña (El Niño) is more dominant on TC activity than El Niño (La Niña) over the western subregion 140–170° E (eastern sub-region, 170–220° E) as expected. We also show that TC numbers are strongly modulated by the IPO phenomenon with, on average, more TCs occurring during the positive phase than during the negative phase of the IPO in both western and eastern sub-regions. We show for the first time (using a long-term reconstructed TC dataset) that the combined phases of El Niño and + IPO account for increased TC activity, as opposed to the combined phase of La Niña and
- Authors: Yeasmin, Alea , Chand, Savin , Sultanova, Nargiz
- Date: 2023
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 43, no. 12 (2023), p. 5422-5443
- Full Text:
- Reviewed:
- Description: Tropical cyclones (TCs) and tropical depressions (TDs), hereafter collectively referred to as tropical storms, often exhibit large year-to-year variability in the South Pacific Ocean basin. Many past studies have examined this variability in relation to the El Niño Southern Oscillation (ENSO) phenomenon, particularly using observational data from the post-satellite era (i.e., after the 1970s when TC observations became more consistent). However, less emphasis is placed on how tropical storms are modulated at interdecadal and decadal time scales such as due to Interdecadal Pacific Oscillation (IPO). This is because post-satellite data are available for relatively short time period (i.e., post-1970s), limiting our understanding of the IPO–TC relationship in the South Pacific. Here, using NOAA-CIRES 20th Century Reanalysis (20CR) dataset, we reconstruct historical records (1871–2014) of TC and depression proxies for the South Pacific Ocean basin, and then utilize these reconstructed proxies to first understand the connections between TC–ENSO and TC–IPO over the 20th century, and then investigate the combined effects of ENSO–IPO effects on TCs and depressions. Results show that La Niña (El Niño) is more dominant on TC activity than El Niño (La Niña) over the western subregion 140–170° E (eastern sub-region, 170–220° E) as expected. We also show that TC numbers are strongly modulated by the IPO phenomenon with, on average, more TCs occurring during the positive phase than during the negative phase of the IPO in both western and eastern sub-regions. We show for the first time (using a long-term reconstructed TC dataset) that the combined phases of El Niño and + IPO account for increased TC activity, as opposed to the combined phase of La Niña and
Declining tropical cyclone frequency under global warming
- Chand, Savin, Walsh, Kevin, Camargo, Suzana, Kossin, James, Tory, Kevin, Wehner, Michael, Chan, Johnny, Klotzbach, Philip, Dowdy, Andrew, Bell, Samuel, Ramsay, Hamish, Murakami, Hiroyuki
- Authors: Chand, Savin , Walsh, Kevin , Camargo, Suzana , Kossin, James , Tory, Kevin , Wehner, Michael , Chan, Johnny , Klotzbach, Philip , Dowdy, Andrew , Bell, Samuel , Ramsay, Hamish , Murakami, Hiroyuki
- Date: 2022
- Type: Text , Journal article
- Relation: Nature Climate Change Vol. 12, no. 7 (2022), p. 655-661
- Full Text:
- Reviewed:
- Description: Assessing the role of anthropogenic warming from temporally inhomogeneous historical data in the presence of large natural variability is difficult and has caused conflicting conclusions on detection and attribution of tropical cyclone (TC) trends. Here, using a reconstructed long-term proxy of annual TC numbers together with high-resolution climate model experiments, we show robust declining trends in the annual number of TCs at global and regional scales during the twentieth century. The Twentieth Century Reanalysis (20CR) dataset is used for reconstruction because, compared with other reanalyses, it assimilates only sea-level pressure fields rather than utilize all available observations in the troposphere, making it less sensitive to temporal inhomogeneities in the observations. It can also capture TC signatures from the pre-satellite era reasonably well. The declining trends found are consistent with the twentieth century weakening of the Hadley and Walker circulations, which make conditions for TC formation less favourable. © 2022, The Author(s).
- Authors: Chand, Savin , Walsh, Kevin , Camargo, Suzana , Kossin, James , Tory, Kevin , Wehner, Michael , Chan, Johnny , Klotzbach, Philip , Dowdy, Andrew , Bell, Samuel , Ramsay, Hamish , Murakami, Hiroyuki
- Date: 2022
- Type: Text , Journal article
- Relation: Nature Climate Change Vol. 12, no. 7 (2022), p. 655-661
- Full Text:
- Reviewed:
- Description: Assessing the role of anthropogenic warming from temporally inhomogeneous historical data in the presence of large natural variability is difficult and has caused conflicting conclusions on detection and attribution of tropical cyclone (TC) trends. Here, using a reconstructed long-term proxy of annual TC numbers together with high-resolution climate model experiments, we show robust declining trends in the annual number of TCs at global and regional scales during the twentieth century. The Twentieth Century Reanalysis (20CR) dataset is used for reconstruction because, compared with other reanalyses, it assimilates only sea-level pressure fields rather than utilize all available observations in the troposphere, making it less sensitive to temporal inhomogeneities in the observations. It can also capture TC signatures from the pre-satellite era reasonably well. The declining trends found are consistent with the twentieth century weakening of the Hadley and Walker circulations, which make conditions for TC formation less favourable. © 2022, The Author(s).
Severe tropical cyclones over southwest Pacific Islands : economic impacts and implications for disaster risk management
- Deo, Anil, Chand, Savin, McIntosh, R. Duncan, Prakash, Bipen, Holbrook, Neil, Magee, Andrew, Haruhiru, Alick, Malsale, Philip
- Authors: Deo, Anil , Chand, Savin , McIntosh, R. Duncan , Prakash, Bipen , Holbrook, Neil , Magee, Andrew , Haruhiru, Alick , Malsale, Philip
- Date: 2022
- Type: Text , Journal article
- Relation: Climatic Change Vol. 172, no. 3-4 (2022), p.
- Full Text:
- Reviewed:
- Description: Tropical cyclones (TCs) are amongst the costliest natural hazards for southwest Pacific (SWP) Island nations. Extreme winds coupled with heavy rainfall and related coastal hazards, such as large waves and high seas, can have devastating consequences for life and property. Effects of anthropogenic climate change are likely to make TCs even more destructive in the SWP (as that observed particularly over Fiji) and elsewhere around the globe, yet TCs may occur less often. However, the underpinning science of quantifying future TC projections amid multiple uncertainties can be complex. The challenge for scientists is how to turn such technical knowledge framed around uncertainties into tangible products to inform decision-making in the disaster risk management (DRM) and disaster risk reduction (DRR) sector. Drawing on experiences from past TC events as analogies to what may happen in a warming climate can be useful. The role of science-based climate services tailored to the needs of the DRM and DRR sector is critical in this context. In the first part of this paper, we examine cases of historically severe TCs in the SWP and quantify their socio-economic impacts. The second part of this paper discusses a decision-support framework developed in collaboration with a number of agencies in the SWP, featuring science-based climate services that inform different stages of planning in national-level risk management strategies. © 2022, The Author(s).
- Authors: Deo, Anil , Chand, Savin , McIntosh, R. Duncan , Prakash, Bipen , Holbrook, Neil , Magee, Andrew , Haruhiru, Alick , Malsale, Philip
- Date: 2022
- Type: Text , Journal article
- Relation: Climatic Change Vol. 172, no. 3-4 (2022), p.
- Full Text:
- Reviewed:
- Description: Tropical cyclones (TCs) are amongst the costliest natural hazards for southwest Pacific (SWP) Island nations. Extreme winds coupled with heavy rainfall and related coastal hazards, such as large waves and high seas, can have devastating consequences for life and property. Effects of anthropogenic climate change are likely to make TCs even more destructive in the SWP (as that observed particularly over Fiji) and elsewhere around the globe, yet TCs may occur less often. However, the underpinning science of quantifying future TC projections amid multiple uncertainties can be complex. The challenge for scientists is how to turn such technical knowledge framed around uncertainties into tangible products to inform decision-making in the disaster risk management (DRM) and disaster risk reduction (DRR) sector. Drawing on experiences from past TC events as analogies to what may happen in a warming climate can be useful. The role of science-based climate services tailored to the needs of the DRM and DRR sector is critical in this context. In the first part of this paper, we examine cases of historically severe TCs in the SWP and quantify their socio-economic impacts. The second part of this paper discusses a decision-support framework developed in collaboration with a number of agencies in the SWP, featuring science-based climate services that inform different stages of planning in national-level risk management strategies. © 2022, The Author(s).
Statistical calibration of long-term reanalysis data for australian fire weather conditions
- Biswas, Soubhik, Chand, Savin, Dowdy, Andrew, Wright, Wendy, Foale, Cameron, Zhao, Xiaohui, Deo, A
- Authors: Biswas, Soubhik , Chand, Savin , Dowdy, Andrew , Wright, Wendy , Foale, Cameron , Zhao, Xiaohui , Deo, A
- Date: 2022
- Type: Text , Journal article
- Relation: Journal of Applied Meteorology and Climatology Vol. 61, no. 6 (2022), p. 729-758
- Full Text: false
- Reviewed:
- Description: Reconstructed weather datasets, such as reanalyses based on model output with data assimilation, often show systematic biases in magnitude when compared with observations. Postprocessing approaches can help adjust the distribution so that the reconstructed data resemble the observed data as closely as possible. In this study, we have compared various statistical bias-correction approaches based on quantile–quantile matching to correct the data from the Twentieth Century Reanalysis, version 2c (20CRv2c), with observation-based data. Methods included in the comparison utilize a suite of different approaches: a linear model, a median-based approach, a nonparametric linear method, a spline-based method, and approaches that are based on the lognormal and Weibull distributions. These methods were applied to daily data in the Australian region for rainfall, maximum temperature, relative humidity, and wind speed. Note that these are the variables required to compute the forest fire danger index (FFDI), widely used in Australia to examine dangerous fire weather conditions. We have compared the relative errors and performances of each method across various locations in Australia and applied the approach with the lowest mean-absolute error across multiple variables to produce a reliable long-term biascorrected FFDI dataset across Australia. The spline-based data correction was found to have some benefits relative to the other methods in better representing the mean FFDI values and the extremes from the observed records for many of the cases examined here. It is intended that this statistical bias-correction approach applied to long-term reanalysis data will help enable new insight on climatological variations in hazardous phenomena, including dangerous wildfires in Australia extending over the past century. © 2022 American Meteorological Society.
Tropical cyclone climatology, variability, and trends in the Tonga region, Southwest Pacific
- Tu'uholoaki, Moleni, Singh, Awnesh, Espejo, Antonio, Chand, Savin, Damlamian, Herve
- Authors: Tu'uholoaki, Moleni , Singh, Awnesh , Espejo, Antonio , Chand, Savin , Damlamian, Herve
- Date: 2022
- Type: Text , Journal article
- Relation: Weather and Climate Extremes Vol. 37, no. (2022), p.
- Full Text:
- Reviewed:
- Description: The focus of several past tropical cyclone (TC) studies in the Southwest Pacific (SWP) had been primarily at the regional scale, with little or no attention to the local-scale TC activity (i.e., at the country level). With the growing coastal population in the South Pacific Island countries, as well as increasing threats from and exposure to climate extremes mostly affecting vulnerable communities, examining TC-related risks at the country level is more imperative now than before. This study catalogues for the first time the climatology, variability and trends of TCs affecting Nuku'alofa, the capital of Tonga using the Southwest Pacific Enhanced Archived for Tropical Cyclone (SPEArTC) dataset for the period between 1970 and 2019. The variability is examined in relation to the El Niño–Southern Oscillation (ENSO) phenomenon, which is the major driver of the year-to-year variability of TC activity in the SWP. A total of 128 TC tracks affected the Tonga region over the study period, with a seasonal average of
- Authors: Tu'uholoaki, Moleni , Singh, Awnesh , Espejo, Antonio , Chand, Savin , Damlamian, Herve
- Date: 2022
- Type: Text , Journal article
- Relation: Weather and Climate Extremes Vol. 37, no. (2022), p.
- Full Text:
- Reviewed:
- Description: The focus of several past tropical cyclone (TC) studies in the Southwest Pacific (SWP) had been primarily at the regional scale, with little or no attention to the local-scale TC activity (i.e., at the country level). With the growing coastal population in the South Pacific Island countries, as well as increasing threats from and exposure to climate extremes mostly affecting vulnerable communities, examining TC-related risks at the country level is more imperative now than before. This study catalogues for the first time the climatology, variability and trends of TCs affecting Nuku'alofa, the capital of Tonga using the Southwest Pacific Enhanced Archived for Tropical Cyclone (SPEArTC) dataset for the period between 1970 and 2019. The variability is examined in relation to the El Niño–Southern Oscillation (ENSO) phenomenon, which is the major driver of the year-to-year variability of TC activity in the SWP. A total of 128 TC tracks affected the Tonga region over the study period, with a seasonal average of
Using historical tropical cyclone climate datasets to examine wind speed recurrence for coastal Australia
- Bell, Samuel, Dowdy, Andrew, Ramsay, H., Chand, Savin, Su, C., Ye, Harvey
- Authors: Bell, Samuel , Dowdy, Andrew , Ramsay, H. , Chand, Savin , Su, C. , Ye, Harvey
- Date: 2022
- Type: Text , Journal article
- Relation: Scientific Reports Vol. 12, no. 1 (2022), p.
- Full Text:
- Reviewed:
- Description: Likelihood estimates of extreme winds, including those from tropical cyclones (TCs) at certain locations are used to inform wind load standards for structural design. Here, wind speed average recurrence intervals (ARIs) determined from TC climate data dating back to the 1970s in two quantile–quantile adjusted reanalysis datasets (ERA5 and BARRA [1990]), and best-track observations for context, were compared with Standardized ARIs (AS/NZS) across seven tropical and two subtropical Australian inland coastal regions. The novelty of this work lies in determining TC-wind speed ARIs from a range of datasets that are not typically used to evaluate this metric. Inherent differences between the data used to determine the Standard ARIs (large sample size allow for larger extrapolations; GEV function) and TC data ARIs (smaller sample size and less certain data; the more asymptotic Lognormal/Weibull functions are used) led to the use of different extreme value functions. Results indicated that although these are two distinct ways of determining design wind speeds, when they are considered equivalent, there was a moderate reproduction of the ARI curves with respect to the Standard in both reanalysis datasets, suggesting that similar analyses using climate model products can provide useful information on these types of metrics with some caveats. Trends in TC wind strength affecting coastal Australia were also analyzed, indicating a potential slight downtrend in tropical West coast TC wind strength and slight uptrend for tropical East coast TC wind strength, noting considerable uncertainty given the short time period and limitations of data quality including over longer time periods. Such trends are not only limited to the relationship between TC intensity and anthropogenic warming, but also to regional changes in TC frequency and track direction. This could lead to significant trends emerging in regional Australian TC wind gust strength before several decades of warming have occurred. It is hoped that climate models can provide both longer-term and a more homogenous base for these types of evaluations and subsequent projections with respect to climate change simulations. © 2022, Crown.
- Authors: Bell, Samuel , Dowdy, Andrew , Ramsay, H. , Chand, Savin , Su, C. , Ye, Harvey
- Date: 2022
- Type: Text , Journal article
- Relation: Scientific Reports Vol. 12, no. 1 (2022), p.
- Full Text:
- Reviewed:
- Description: Likelihood estimates of extreme winds, including those from tropical cyclones (TCs) at certain locations are used to inform wind load standards for structural design. Here, wind speed average recurrence intervals (ARIs) determined from TC climate data dating back to the 1970s in two quantile–quantile adjusted reanalysis datasets (ERA5 and BARRA [1990]), and best-track observations for context, were compared with Standardized ARIs (AS/NZS) across seven tropical and two subtropical Australian inland coastal regions. The novelty of this work lies in determining TC-wind speed ARIs from a range of datasets that are not typically used to evaluate this metric. Inherent differences between the data used to determine the Standard ARIs (large sample size allow for larger extrapolations; GEV function) and TC data ARIs (smaller sample size and less certain data; the more asymptotic Lognormal/Weibull functions are used) led to the use of different extreme value functions. Results indicated that although these are two distinct ways of determining design wind speeds, when they are considered equivalent, there was a moderate reproduction of the ARI curves with respect to the Standard in both reanalysis datasets, suggesting that similar analyses using climate model products can provide useful information on these types of metrics with some caveats. Trends in TC wind strength affecting coastal Australia were also analyzed, indicating a potential slight downtrend in tropical West coast TC wind strength and slight uptrend for tropical East coast TC wind strength, noting considerable uncertainty given the short time period and limitations of data quality including over longer time periods. Such trends are not only limited to the relationship between TC intensity and anthropogenic warming, but also to regional changes in TC frequency and track direction. This could lead to significant trends emerging in regional Australian TC wind gust strength before several decades of warming have occurred. It is hoped that climate models can provide both longer-term and a more homogenous base for these types of evaluations and subsequent projections with respect to climate change simulations. © 2022, Crown.
- Yeasmin, Alea, Chand, Savin, Turville, Christopher, Sultanova, Nargiz
- Authors: Yeasmin, Alea , Chand, Savin , Turville, Christopher , Sultanova, Nargiz
- Date: 2021
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 41, no. 11 (2021), p. 5318-5330
- Full Text: false
- Reviewed:
- Description: Tropical cyclones (TCs) are one of the most destructive synoptic systems and can cause enormous loss of life and property damages in the South Pacific island nations. The impact of tropical depressions (TDs, i.e. weaker systems that do not develop into TCs) can also be staggering in the region in terms of heavy flooding and landslides, but a lack of complete records often hinders research involving TD impacts. A methodology has been developed here to detect TDs in the ERA-5 reanalysis dataset (the fifth generation ECMWF atmospheric reanalysis of the global climate) using the Okubo–Weiss–Zeta parameter (OWZP) detection scheme. The new South Pacific Enhanced Archive for Tropical Cyclones dataset (SPEArTC), the Dvorak analysis of satellite-based cloud patterns over the South Pacific Ocean basin, and a rainfall dataset for various stations and historical archives have been utilized to validate ERA5-derived TCs and TDs for the period between 1979 and 2019. Results indicate that the OWZP method shows substantial skill in capturing the realistic climatological distribution of TDs (as well as TCs) for the South Pacific Ocean in the ERA5 reanalysis, paving a way forward for future climatological studies involving the impacts of TCs and TDs over the island nations using longer-term reanalyses products such as the 20th-century reanalysis dataset that extends back to the 1850s. © 2021 Royal Meteorological Society
Tropical cyclone contribution to extreme rainfall over southwest Pacific Island nations
- Deo, Anil, Chand, Savin, Ramsay, Hamish, Holbrook, Neil, McGree, Simon
- Authors: Deo, Anil , Chand, Savin , Ramsay, Hamish , Holbrook, Neil , McGree, Simon
- Date: 2021
- Type: Text , Journal article
- Relation: Climate Dynamics Vol. 56, no. 11-12 (2021), p. 3967-3993
- Full Text:
- Reviewed:
- Description: Southwest Pacific nations are among some of the worst impacted and most vulnerable globally in terms of tropical cyclone (TC)-induced flooding and accompanying risks. This study objectively quantifies the fractional contribution of TCs to extreme rainfall (hereafter, TC contributions) in the context of climate variability and change. We show that TC contributions to extreme rainfall are substantially enhanced during active phases of the Madden–Julian Oscillation and by El Niño conditions (particularly over the eastern southwest Pacific region); this enhancement is primarily attributed to increased TC activity during these event periods. There are also indications of increasing intensities of TC-induced extreme rainfall events over the past few decades. A key part of this work involves development of sophisticated Bayesian regression models for individual island nations in order to better understand the synergistic relationships between TC-induced extreme rainfall and combinations of various climatic drivers that modulate the relationship. Such models are found to be very useful for not only assessing probabilities of TC- and non-TC induced extreme rainfall events but also evaluating probabilities of extreme rainfall for cases with different underlying climatic conditions. For example, TC-induced extreme rainfall probability over Samoa can vary from ~ 95 to ~ 75% during a La Niña period, if it coincides with an active or inactive phase of the MJO, and can be reduced to ~ 30% during a combination of El Niño period and inactive phase of the MJO. Several other such cases have been assessed for different island nations, providing information that have potentially important implications for planning and preparing for TC risks in vulnerable Pacific Island nations. © 2021, The Author(s). *Please note that there are multiple authors for this article therefore only the name of the first 5 including Federation University Australia affiliate “Anil Deo and Savin Chand” is provided in this record**
- Authors: Deo, Anil , Chand, Savin , Ramsay, Hamish , Holbrook, Neil , McGree, Simon
- Date: 2021
- Type: Text , Journal article
- Relation: Climate Dynamics Vol. 56, no. 11-12 (2021), p. 3967-3993
- Full Text:
- Reviewed:
- Description: Southwest Pacific nations are among some of the worst impacted and most vulnerable globally in terms of tropical cyclone (TC)-induced flooding and accompanying risks. This study objectively quantifies the fractional contribution of TCs to extreme rainfall (hereafter, TC contributions) in the context of climate variability and change. We show that TC contributions to extreme rainfall are substantially enhanced during active phases of the Madden–Julian Oscillation and by El Niño conditions (particularly over the eastern southwest Pacific region); this enhancement is primarily attributed to increased TC activity during these event periods. There are also indications of increasing intensities of TC-induced extreme rainfall events over the past few decades. A key part of this work involves development of sophisticated Bayesian regression models for individual island nations in order to better understand the synergistic relationships between TC-induced extreme rainfall and combinations of various climatic drivers that modulate the relationship. Such models are found to be very useful for not only assessing probabilities of TC- and non-TC induced extreme rainfall events but also evaluating probabilities of extreme rainfall for cases with different underlying climatic conditions. For example, TC-induced extreme rainfall probability over Samoa can vary from ~ 95 to ~ 75% during a La Niña period, if it coincides with an active or inactive phase of the MJO, and can be reduced to ~ 30% during a combination of El Niño period and inactive phase of the MJO. Several other such cases have been assessed for different island nations, providing information that have potentially important implications for planning and preparing for TC risks in vulnerable Pacific Island nations. © 2021, The Author(s). *Please note that there are multiple authors for this article therefore only the name of the first 5 including Federation University Australia affiliate “Anil Deo and Savin Chand” is provided in this record**
Tropical cyclone-induced extreme winds in climate datasets: East coast of Australia
- Bell, Samuel, Chand, Savin, Dowdy, Andrew, Ramsay, Hamish, Deo, Anil
- Authors: Bell, Samuel , Chand, Savin , Dowdy, Andrew , Ramsay, Hamish , Deo, Anil
- Date: 2021
- Type: Text , Conference paper
- Relation: 24th International Congress on Modelling and Simulation; Sydney, NSW; Australia, 5 to 10 December 2021 in mssanz.org.au/modsim2021
- Full Text:
- Reviewed:
- Description: Extreme wind speeds, which are typically induced by tropical cyclones (TCs) in coastal regions of tropical Australia, are an important hazard to consider in the context of climate change. Here, a range of climate datasets based on direct observations, reanalyses and regional climate model simulations are used to examine trends in TC-related extreme winds over coastal Eastern Australia. Wind gust speed estimates from best-track data and automatic weather station (AWS) observations are used to calibrate reanalysis wind gusts from the Bureau of Meteorology (BoM) Atmospheric high-resolution Regional Reanalysis for Australia (BARRA) and from the global ERA5 reanalysis. Together, these different datasets provide complementary lines of evidence in relation to historical changes in extreme wind gust speeds. Differences between the occurrence frequency of TC-related wind gusts reaching Category 4/5 on the Australian TC intensity scale and the return periods of TC-related wind gusts over three decades (1990–2019) are presented. Lognormal and Weibull curves are fitted to the extreme value wind speeds and used to provide estimates of associated return periods. Results indicate that the East coast has likely experienced a slightly increased frequency of extreme wind gusts from TCs over the more recent time period (2005–2019), noting considerable uncertainties around these extremes given the limitations of the available data, including that of rapidly evolving observational practices and short time period. Projection results from climate models provide can provide a more homogenous evaluation of the impacts of climate change over a longer time period than is currently available, despite having their own limitations such as model biases and inaccurate representation of certain climate processes. The same experimental methods applied to the observational datasets, are here applied to future projections based on several regional climate model (RCM) simulations under high emission scenarios: NSW and ACT Regional Climate Modelling (NARCliM), CSIRO Conformal Cubic Atmospheric Model (CCAM) and BoM’s Atmospheric Regional Projections for Australia (BARPA). NARCliM results are downscaled from a selection CMIP3 models and use a mean wind speed rather than a gust, while CCAM and BARPA results are downscaled from a selection of CMIP5 models. Results from these projections on extreme wind speeds are generally inconclusive for climate trends on the East coast but indicated that an increase in intensity would be more likely than a decrease in a warmer world. Small sample size and considerable interannual variability in landfalling severe TCs means that there are considerable uncertainties around long-term observed trends in their occurrence. However, a small increase in the observed occurrence frequency of severe TCs for the East coast is noted here based on observations, such that an increase in the more damaging wind gust speeds associated with severe TCs (i.e., rare events with higher return period values) is a plausible outcome for the future climate of Eastern Australia. For example, the return period projections from the regional climate models generally suggest an increase is more likely than a decrease for the most extreme wind gust speeds. We note that whether a change in long-term return periods of wind gusts or a change in the frequency of TC landfalls of any intensity is more important is likely specific to the region or application being considered. Although there are considerable uncertainties around this topic of extreme wind gusts and TCs in a changing climate, our findings are intended to help contribute to the range of guidance available in relation to managing climate risk in Eastern Australia.
- Authors: Bell, Samuel , Chand, Savin , Dowdy, Andrew , Ramsay, Hamish , Deo, Anil
- Date: 2021
- Type: Text , Conference paper
- Relation: 24th International Congress on Modelling and Simulation; Sydney, NSW; Australia, 5 to 10 December 2021 in mssanz.org.au/modsim2021
- Full Text:
- Reviewed:
- Description: Extreme wind speeds, which are typically induced by tropical cyclones (TCs) in coastal regions of tropical Australia, are an important hazard to consider in the context of climate change. Here, a range of climate datasets based on direct observations, reanalyses and regional climate model simulations are used to examine trends in TC-related extreme winds over coastal Eastern Australia. Wind gust speed estimates from best-track data and automatic weather station (AWS) observations are used to calibrate reanalysis wind gusts from the Bureau of Meteorology (BoM) Atmospheric high-resolution Regional Reanalysis for Australia (BARRA) and from the global ERA5 reanalysis. Together, these different datasets provide complementary lines of evidence in relation to historical changes in extreme wind gust speeds. Differences between the occurrence frequency of TC-related wind gusts reaching Category 4/5 on the Australian TC intensity scale and the return periods of TC-related wind gusts over three decades (1990–2019) are presented. Lognormal and Weibull curves are fitted to the extreme value wind speeds and used to provide estimates of associated return periods. Results indicate that the East coast has likely experienced a slightly increased frequency of extreme wind gusts from TCs over the more recent time period (2005–2019), noting considerable uncertainties around these extremes given the limitations of the available data, including that of rapidly evolving observational practices and short time period. Projection results from climate models provide can provide a more homogenous evaluation of the impacts of climate change over a longer time period than is currently available, despite having their own limitations such as model biases and inaccurate representation of certain climate processes. The same experimental methods applied to the observational datasets, are here applied to future projections based on several regional climate model (RCM) simulations under high emission scenarios: NSW and ACT Regional Climate Modelling (NARCliM), CSIRO Conformal Cubic Atmospheric Model (CCAM) and BoM’s Atmospheric Regional Projections for Australia (BARPA). NARCliM results are downscaled from a selection CMIP3 models and use a mean wind speed rather than a gust, while CCAM and BARPA results are downscaled from a selection of CMIP5 models. Results from these projections on extreme wind speeds are generally inconclusive for climate trends on the East coast but indicated that an increase in intensity would be more likely than a decrease in a warmer world. Small sample size and considerable interannual variability in landfalling severe TCs means that there are considerable uncertainties around long-term observed trends in their occurrence. However, a small increase in the observed occurrence frequency of severe TCs for the East coast is noted here based on observations, such that an increase in the more damaging wind gust speeds associated with severe TCs (i.e., rare events with higher return period values) is a plausible outcome for the future climate of Eastern Australia. For example, the return period projections from the regional climate models generally suggest an increase is more likely than a decrease for the most extreme wind gust speeds. We note that whether a change in long-term return periods of wind gusts or a change in the frequency of TC landfalls of any intensity is more important is likely specific to the region or application being considered. Although there are considerable uncertainties around this topic of extreme wind gusts and TCs in a changing climate, our findings are intended to help contribute to the range of guidance available in relation to managing climate risk in Eastern Australia.
- Chand, Savin, Dowdy, Andrew, Bell, Samuel, Tory, Kevin
- Authors: Chand, Savin , Dowdy, Andrew , Bell, Samuel , Tory, Kevin
- Date: 2020
- Type: Text , Book chapter
- Relation: Springer Climate p. 251-273
- Full Text: false
- Reviewed:
- Description: Impacts of tropical cyclones in the South Pacific Island countries are of great significance. Now with the growing threats from human-induced climate change, the need for effective disaster risk management and adaptation strategies for these island countries is more important than before. In order to implement appropriate strategies, a comprehensive understanding of South Pacific tropical cyclone activity—and how it is likely to change as a result of human-induced climate change—is essential. While a number of past studies have examined various aspects of tropical cyclone activity in the South Pacific basin, a review that consolidates those studies with new information is essential. In this chapter, we first examine tropical cyclone data quality for the South Pacific basin and then review the robustness of the relationship between South Pacific tropical cyclones and drivers of natural climate variability. Note that an understanding of the limitations of the data quality is important to determine the extent of natural climate variability and signatures—if any—of human-induced climate change on tropical cyclones. We then examine the influence of climate change on tropical cyclones using up-to-date historical observations and climate model projections. © Springer Nature Switzerland AG 2020.
Climate change scenarios and projections for the pacific
- Authors: Chand, Savin
- Date: 2020
- Type: Text , Book chapter
- Relation: Springer Climate 3 p. 171-199
- Full Text: false
- Reviewed:
- Description: Small island countries in the Pacific have characteristics which enhance their vulnerability and reduce their resilience to the effects of climate change, sea-level rise and extreme events. Over the past decade, a number of studies have been undertaken to improve our understanding of climate variability and change in the Pacific. This chapter provides an overview of those studies and discusses possible challenges associated with climate model projections for the small island countries in the Pacific. © Springer Nature Switzerland AG 2020.
North Indian ocean tropical cyclone activity in CMIP5 experiments : future projections using a model-independent detection and tracking scheme
- Bell, Samuel, Chand, Savin, Tory, Kevin, Ye, Hua, Turville, Christopher
- Authors: Bell, Samuel , Chand, Savin , Tory, Kevin , Ye, Hua , Turville, Christopher
- Date: 2020
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 40, no. 15 (2020), p. 6492-6505
- Full Text:
- Reviewed:
- Description: The sensitivity of tropical cyclone (TC) projection results to different models and the detection and tracking scheme used is well established. In this study, future climate projections of TC activity in the North Indian Ocean (NIO) are assessed with a model- and basin-independent detection and tracking scheme. The scheme is applied to selected models from the coupled model intercomparison project phase 5 (CMIP5) experiments forced under the historical and representative concentration pathway 8.5 (RCP8.5) conditions. Most models underestimated the frequency of early season (April–June) TCs and contained genesis biases equatorward of ~7.5°N in comparison to the historical records. TC tracks detected in reanalysis and model data were input to a clustering algorithm simultaneously, with two clusters in the Arabian Sea and two in the Bay of Bengal (k = 4). Projection results indicated a slight decrease of overall TC genesis frequency in the NIO, with an increase of TC genesis frequency in the Arabian Sea (30–64%) and a decrease in the Bay of Bengal (22–43%), consistent between clusters in each of these sub-regions. These changes were largely due to changes in the pre-monsoon season (April–June) where Bay of Bengal TCs significantly decreased, consistent with changes in vertical ascent. Northern Arabian Sea TCs significantly increased during the pre-monsoon season, consistent with changes in vertical wind shear and relative humidity. There was a projected increase of TC frequency in the post-monsoon season (October–December), consistent with changes in relative humidity and vertical ascent, although not all clusters followed this trend; noting a different response in the southern Bay of Bengal. In turn, these projections caused changes to the climate averaged TC track density, including a decrease (up to 2 TCs per decade) affecting the eastern coast of India and a small increase (up to 0.5 TCs per decade) affecting eastern Africa, Oman and Yemen. © 2020 Royal Meteorological Society
- Authors: Bell, Samuel , Chand, Savin , Tory, Kevin , Ye, Hua , Turville, Christopher
- Date: 2020
- Type: Text , Journal article
- Relation: International Journal of Climatology Vol. 40, no. 15 (2020), p. 6492-6505
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- Description: The sensitivity of tropical cyclone (TC) projection results to different models and the detection and tracking scheme used is well established. In this study, future climate projections of TC activity in the North Indian Ocean (NIO) are assessed with a model- and basin-independent detection and tracking scheme. The scheme is applied to selected models from the coupled model intercomparison project phase 5 (CMIP5) experiments forced under the historical and representative concentration pathway 8.5 (RCP8.5) conditions. Most models underestimated the frequency of early season (April–June) TCs and contained genesis biases equatorward of ~7.5°N in comparison to the historical records. TC tracks detected in reanalysis and model data were input to a clustering algorithm simultaneously, with two clusters in the Arabian Sea and two in the Bay of Bengal (k = 4). Projection results indicated a slight decrease of overall TC genesis frequency in the NIO, with an increase of TC genesis frequency in the Arabian Sea (30–64%) and a decrease in the Bay of Bengal (22–43%), consistent between clusters in each of these sub-regions. These changes were largely due to changes in the pre-monsoon season (April–June) where Bay of Bengal TCs significantly decreased, consistent with changes in vertical ascent. Northern Arabian Sea TCs significantly increased during the pre-monsoon season, consistent with changes in vertical wind shear and relative humidity. There was a projected increase of TC frequency in the post-monsoon season (October–December), consistent with changes in relative humidity and vertical ascent, although not all clusters followed this trend; noting a different response in the southern Bay of Bengal. In turn, these projections caused changes to the climate averaged TC track density, including a decrease (up to 2 TCs per decade) affecting the eastern coast of India and a small increase (up to 0.5 TCs per decade) affecting eastern Africa, Oman and Yemen. © 2020 Royal Meteorological Society