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
- 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
- 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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- Reviewed:
- 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
- Full Text:
- Reviewed:
- 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:
- Reviewed:
- 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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- 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.
- 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
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- 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
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- 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:
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- 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).
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.
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- 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.
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- 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:
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- 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.
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
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- 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:
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- 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**
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
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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
- 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
Projected changes in ENSO-driven regional tropical cyclone tracks
- Bell, Samuel, Chand, Savin, Turville, Christopher
- Authors: Bell, Samuel , Chand, Savin , Turville, Christopher
- Date: 2020
- Type: Text , Journal article
- Relation: Climate Dynamics Vol. 54, no. 3-4 (Feb 2020), p. 2533-2559
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- Description: Simulations and projections of the El Nino Southern Oscillation's (ENSO's) influence on TC track variability was analysed globally using Coupled Model Intercomparison project Phase 5 (CMIP5) models. The ability of these models to simulate the historical (1970-2000) ENSO-TC track relationship and inform us of the likely projected changes resulting from high carbon emissions (RCP8.5) in a climate projection (2070-2100) was determined through cluster analysis. The number of seasonal TC occurrences during traditional ENSO events ("El Nino" and "La Nina") in each cluster were used to determine whether each cluster was "El Nino dominant", "La Nina dominant" or "neither". Only seven out of a combined total of 28 clusters across all basins were found to disagree in terms of "ENSO dominance" between the observed records and historical model simulations. This suggests that models can simulate the ENSO and TC track relationship reasonably well. Under sustained high carbon emissions, La Nina TCs were projected to become dominant over El Nino TCs in the central South Indian Ocean ( 60-100 degrees E), the southern Bay of Bengal and over straight-moving TCs in the South China Sea. El Nino TCs were projected to increase and become dominant over La Nina TCs in a larger area of the western South Pacific ( 160 degrees E-165 degrees W) and central North Pacific ( 160 degrees E-145 degrees W) Oceans. Projections of track directions and lifetimes, while less robust, indicated that El Nino TCs would track westward more often in the Coral Sea (150-165 degrees E), while El Nino TCs that took an eastward track here would have longer lifetimes ( 3 days).
- Authors: Bell, Samuel , Chand, Savin , Turville, Christopher
- Date: 2020
- Type: Text , Journal article
- Relation: Climate Dynamics Vol. 54, no. 3-4 (Feb 2020), p. 2533-2559
- Full Text:
- Reviewed:
- Description: Simulations and projections of the El Nino Southern Oscillation's (ENSO's) influence on TC track variability was analysed globally using Coupled Model Intercomparison project Phase 5 (CMIP5) models. The ability of these models to simulate the historical (1970-2000) ENSO-TC track relationship and inform us of the likely projected changes resulting from high carbon emissions (RCP8.5) in a climate projection (2070-2100) was determined through cluster analysis. The number of seasonal TC occurrences during traditional ENSO events ("El Nino" and "La Nina") in each cluster were used to determine whether each cluster was "El Nino dominant", "La Nina dominant" or "neither". Only seven out of a combined total of 28 clusters across all basins were found to disagree in terms of "ENSO dominance" between the observed records and historical model simulations. This suggests that models can simulate the ENSO and TC track relationship reasonably well. Under sustained high carbon emissions, La Nina TCs were projected to become dominant over El Nino TCs in the central South Indian Ocean ( 60-100 degrees E), the southern Bay of Bengal and over straight-moving TCs in the South China Sea. El Nino TCs were projected to increase and become dominant over La Nina TCs in a larger area of the western South Pacific ( 160 degrees E-165 degrees W) and central North Pacific ( 160 degrees E-145 degrees W) Oceans. Projections of track directions and lifetimes, while less robust, indicated that El Nino TCs would track westward more often in the Coral Sea (150-165 degrees E), while El Nino TCs that took an eastward track here would have longer lifetimes ( 3 days).
Projections of southern hemisphere tropical cyclone track density using CMIP5 models
- Bell, Samuel, Chand, Savin, Tory, Kevin, Dowdy, Andrew, Turville, Christopher, Ye, Harvey
- Authors: Bell, Samuel , Chand, Savin , Tory, Kevin , Dowdy, Andrew , Turville, Christopher , Ye, Harvey
- Date: 2019
- Type: Text , Journal article
- Relation: Climate Dynamics Vol. 52, no. 9-10 (2019), p. 6065-6079
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- Description: A recently validated algorithm for detecting and tracking tropical cyclones (TCs) in coarse resolution climate models was applied to a selected group of 12 models from the Coupled Model Intercomparison Project (CMIP5) to assess potential changes in TC track characteristics in the Southern Hemisphere (SH) due to greenhouse warming. Current-climate simulations over the period 1970–2000 are first evaluated against observations using measures of TC genesis location and frequency, as well as track trajectory and lifetime in seven objectively defined genesis regions. The 12-model (12-M) ensemble showed substantial skill in reproducing a realistic TC climatology over the evaluation period. To address potential biases associated with model interdependency, analyses were repeated with an ensemble of five independent models (5-M). Results from both the 12-M and 5-M ensembles were very similar, instilling confidence in the models for climate projections if the current TC-climate relationship is to remain stationary. Projected changes in TC track density between the current- and future-climate (2070–2100) simulations under the Representatives Concentration 8.5 Pathways (RCP8.5) are also assessed. Overall, projection results showed a substantial decrease (~ 1–3 per decade) in track density over most parts of the SH by the end of the twenty-first century. This decrease is attributed to a significant reduction in TC numbers (~ 15–42%) consistent with changes in large-scale environmental parameters such as relative vorticity, environmental vertical wind shear and relative humidity. This study may assist with adaption pathways and implications for regional-scale climate change for vulnerable regions in the SH.
- Authors: Bell, Samuel , Chand, Savin , Tory, Kevin , Dowdy, Andrew , Turville, Christopher , Ye, Harvey
- Date: 2019
- Type: Text , Journal article
- Relation: Climate Dynamics Vol. 52, no. 9-10 (2019), p. 6065-6079
- Full Text:
- Reviewed:
- Description: A recently validated algorithm for detecting and tracking tropical cyclones (TCs) in coarse resolution climate models was applied to a selected group of 12 models from the Coupled Model Intercomparison Project (CMIP5) to assess potential changes in TC track characteristics in the Southern Hemisphere (SH) due to greenhouse warming. Current-climate simulations over the period 1970–2000 are first evaluated against observations using measures of TC genesis location and frequency, as well as track trajectory and lifetime in seven objectively defined genesis regions. The 12-model (12-M) ensemble showed substantial skill in reproducing a realistic TC climatology over the evaluation period. To address potential biases associated with model interdependency, analyses were repeated with an ensemble of five independent models (5-M). Results from both the 12-M and 5-M ensembles were very similar, instilling confidence in the models for climate projections if the current TC-climate relationship is to remain stationary. Projected changes in TC track density between the current- and future-climate (2070–2100) simulations under the Representatives Concentration 8.5 Pathways (RCP8.5) are also assessed. Overall, projection results showed a substantial decrease (~ 1–3 per decade) in track density over most parts of the SH by the end of the twenty-first century. This decrease is attributed to a significant reduction in TC numbers (~ 15–42%) consistent with changes in large-scale environmental parameters such as relative vorticity, environmental vertical wind shear and relative humidity. This study may assist with adaption pathways and implications for regional-scale climate change for vulnerable regions in the SH.
Review of tropical cyclones in the Australian region : Climatology, variability, predictability, and trends
- Chand, Savin, Dowdy, Andrew, Ramsay, Hamish, Walsh, Kevin, Tory, Kevin, Power, Scott, Bell, Samuel, Lavender, Sally, Ye, Hua, Kuleshov, Yuri
- Authors: Chand, Savin , Dowdy, Andrew , Ramsay, Hamish , Walsh, Kevin , Tory, Kevin , Power, Scott , Bell, Samuel , Lavender, Sally , Ye, Hua , Kuleshov, Yuri
- Date: 2019
- Type: Text , Journal article , Review
- Relation: Wiley Interdisciplinary Reviews: Climate Change Vol. 10, no. 5 (2019), p. 1-17
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- Description: Tropical cyclones (TCs) can have severe impacts on Australia. These include extreme rainfall and winds, and coastal hazards such as destructive waves, storm surges, estuarine flooding, and coastal erosion. Various aspects of TCs in the Australian region have been documented over the past several decades. In recent years, increasing emphasis has been placed on human-induced climate change effects on TCs in the Australian region and elsewhere around the globe. However, large natural variability and the lack of consistent long-term TC observations have often complicated the detection and attribution of TC trends. Efforts have been made to improve TC records for Australia over the past decades, but it is still unclear whether such records are sufficient to provide better understanding of the impacts of natural climate variability and climate change. It is important to note that the damage costs associated with tropical cyclones in Australia have increased in recent decades and will continue to increase due to growing coastal settlement and infrastructure development. Therefore, it is critical that any coastal infrastructure planning and engineering decisions, as well as disaster management decisions, strongly consider future risks from tropical cyclones. A better understanding of tropical cyclones in a changing climate will provide key insights that can help mitigate impacts of tropical cyclones on vulnerable communities. An objective assessment of the Australian TCs at regional scale and its link with climate variability and change using improved and up-to-date data records is more imperative now than before. This article is categorized under: Paleoclimates and Current Trends > Modern Climate Change.
- Authors: Chand, Savin , Dowdy, Andrew , Ramsay, Hamish , Walsh, Kevin , Tory, Kevin , Power, Scott , Bell, Samuel , Lavender, Sally , Ye, Hua , Kuleshov, Yuri
- Date: 2019
- Type: Text , Journal article , Review
- Relation: Wiley Interdisciplinary Reviews: Climate Change Vol. 10, no. 5 (2019), p. 1-17
- Full Text:
- Reviewed:
- Description: Tropical cyclones (TCs) can have severe impacts on Australia. These include extreme rainfall and winds, and coastal hazards such as destructive waves, storm surges, estuarine flooding, and coastal erosion. Various aspects of TCs in the Australian region have been documented over the past several decades. In recent years, increasing emphasis has been placed on human-induced climate change effects on TCs in the Australian region and elsewhere around the globe. However, large natural variability and the lack of consistent long-term TC observations have often complicated the detection and attribution of TC trends. Efforts have been made to improve TC records for Australia over the past decades, but it is still unclear whether such records are sufficient to provide better understanding of the impacts of natural climate variability and climate change. It is important to note that the damage costs associated with tropical cyclones in Australia have increased in recent decades and will continue to increase due to growing coastal settlement and infrastructure development. Therefore, it is critical that any coastal infrastructure planning and engineering decisions, as well as disaster management decisions, strongly consider future risks from tropical cyclones. A better understanding of tropical cyclones in a changing climate will provide key insights that can help mitigate impacts of tropical cyclones on vulnerable communities. An objective assessment of the Australian TCs at regional scale and its link with climate variability and change using improved and up-to-date data records is more imperative now than before. This article is categorized under: Paleoclimates and Current Trends > Modern Climate Change.
Western north pacific tropical cyclone tracks in cmip5 models : statistical assessment using a model-independent detection and tracking scheme
- Bell, Samuel, Chand, Savin, Camargo, Suzana, Tory, Kevin, Turville, Chris, Ye, Harvey
- Authors: Bell, Samuel , Chand, Savin , Camargo, Suzana , Tory, Kevin , Turville, Chris , Ye, Harvey
- Date: 2019
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 32, no. 21 (2019), p. 7191-7208
- Full Text:
- Reviewed:
- Description: Past studies have shown that tropical cyclone (TC) projection results can be sensitive to different types of TC tracking schemes, and that the relative adjustments of detection criteria to accommodate different models may not necessarily provide a consistent platform for comparison of projection results. Here, future climate projections of TC activity in the western North Pacific basin (WNP, defined from 0°-50°NAND 100°E-180°) are assessed with a model-independent detection and tracking scheme. This scheme is applied to models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) forced under the historical and representative concentration pathway 8.5 (RCP8.5) conditions. TC tracks from the observed records and independent models are analyzed simultaneously with a curve-clustering algorithm, allowing observed and model tracks to be projected onto the same set of clusters (k =9). Four of the nine clusters were projected to undergo significant changes in TC frequency. Straight-moving TCs in the South China Sea were projected to significantly decrease. Projected increases in TC frequency were found poleward of 20°N and east of 160°E, consistent with changes in ascending motion, as well as vertical wind shear and relative humidity respectively. Projections of TC track exposure indicated significant reductions for southern China and the Philippines and significant increases for the Korean peninsula and Japan, although very few model TCs reached the latter subtropical regions in comparison to the observations. The use of a fundamentally different detection methodology that overcomes the detector/tracker bias gives increased certainty to projections as best as lowresolution simulations can offer. © 2019 American Meteorological Society.
- Authors: Bell, Samuel , Chand, Savin , Camargo, Suzana , Tory, Kevin , Turville, Chris , Ye, Harvey
- Date: 2019
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 32, no. 21 (2019), p. 7191-7208
- Full Text:
- Reviewed:
- Description: Past studies have shown that tropical cyclone (TC) projection results can be sensitive to different types of TC tracking schemes, and that the relative adjustments of detection criteria to accommodate different models may not necessarily provide a consistent platform for comparison of projection results. Here, future climate projections of TC activity in the western North Pacific basin (WNP, defined from 0°-50°NAND 100°E-180°) are assessed with a model-independent detection and tracking scheme. This scheme is applied to models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) forced under the historical and representative concentration pathway 8.5 (RCP8.5) conditions. TC tracks from the observed records and independent models are analyzed simultaneously with a curve-clustering algorithm, allowing observed and model tracks to be projected onto the same set of clusters (k =9). Four of the nine clusters were projected to undergo significant changes in TC frequency. Straight-moving TCs in the South China Sea were projected to significantly decrease. Projected increases in TC frequency were found poleward of 20°N and east of 160°E, consistent with changes in ascending motion, as well as vertical wind shear and relative humidity respectively. Projections of TC track exposure indicated significant reductions for southern China and the Philippines and significant increases for the Korean peninsula and Japan, although very few model TCs reached the latter subtropical regions in comparison to the observations. The use of a fundamentally different detection methodology that overcomes the detector/tracker bias gives increased certainty to projections as best as lowresolution simulations can offer. © 2019 American Meteorological Society.
A statistical assessment of Southern Hemisphere tropical cyclone tracks in climate models
- Ramsay, Hamish, Chand, Savin, Camargo, Suzana
- Authors: Ramsay, Hamish , Chand, Savin , Camargo, Suzana
- Date: 2018
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 31, no. 24 (2018), p. 10081-10104
- Full Text:
- Reviewed:
- Description: Reliable projections of future changes in tropical cyclone (TC) characteristics are highly dependent on the ability of global climate models (GCMs) to simulate the observed characteristics of TCs (i.e., their frequency, genesis locations, movement, and intensity). Here, we investigate the performance of a suite of GCMs from the U.S. CLIVAR Working Group on Hurricanes in simulating observed climatological features of TCs in the Southern Hemisphere. A subset of these GCMs is also explored under three idealized warming scenarios. Two types of simulated TC tracks are evaluated on the basis of a commonly applied cluster analysis: 1) explicitly simulated tracks, and 2) downscaled tracks, derived from a statistical-dynamical technique that depends on the models' large-scale environmental fields. Climatological TC properties such as genesis locations, annual frequency, lifetime maximum intensity (LMI), and seasonality are evaluated for both track types. Future changes to annual frequency, LMI, and the latitude of LMI are evaluated using the downscaled tracks where large sample sizes allow for statistically robust results. An ensemble approach is used to assess future changes of explicit tracks owing to their small number of realizations. We show that the downscaled tracks generally outperform the explicit tracks in relation to many of the climatological features of Southern Hemisphere TCs, despite a few notable biases. Future changes to the frequency and intensity of TCs in the downscaled simulations are found to be highly dependent on the warming scenario and model, with the most robust result being an increase in the LMI under a uniform 2°C surface warming.
- Authors: Ramsay, Hamish , Chand, Savin , Camargo, Suzana
- Date: 2018
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 31, no. 24 (2018), p. 10081-10104
- Full Text:
- Reviewed:
- Description: Reliable projections of future changes in tropical cyclone (TC) characteristics are highly dependent on the ability of global climate models (GCMs) to simulate the observed characteristics of TCs (i.e., their frequency, genesis locations, movement, and intensity). Here, we investigate the performance of a suite of GCMs from the U.S. CLIVAR Working Group on Hurricanes in simulating observed climatological features of TCs in the Southern Hemisphere. A subset of these GCMs is also explored under three idealized warming scenarios. Two types of simulated TC tracks are evaluated on the basis of a commonly applied cluster analysis: 1) explicitly simulated tracks, and 2) downscaled tracks, derived from a statistical-dynamical technique that depends on the models' large-scale environmental fields. Climatological TC properties such as genesis locations, annual frequency, lifetime maximum intensity (LMI), and seasonality are evaluated for both track types. Future changes to annual frequency, LMI, and the latitude of LMI are evaluated using the downscaled tracks where large sample sizes allow for statistically robust results. An ensemble approach is used to assess future changes of explicit tracks owing to their small number of realizations. We show that the downscaled tracks generally outperform the explicit tracks in relation to many of the climatological features of Southern Hemisphere TCs, despite a few notable biases. Future changes to the frequency and intensity of TCs in the downscaled simulations are found to be highly dependent on the warming scenario and model, with the most robust result being an increase in the LMI under a uniform 2°C surface warming.
Statistical assessment of the OWZ Tropical Cyclone Tracking Scheme in ERA-Interim
- Bell, Samuel, Chand, Savin, Tory, Kevin, Turville, Christopher
- Authors: Bell, Samuel , Chand, Savin , Tory, Kevin , Turville, Christopher
- Date: 2018
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 31, no. 6 (2018), p. 2217-2232
- Full Text:
- Reviewed:
- Description: The Okubo–Weiss–Zeta (OWZ) tropical cyclone (TC) detection scheme, which has been used to detect TCs in climate, seasonal prediction, and weather forecast models, is assessed on its ability to produce a realistic TC track climatology in the ERA-Interim product over the 25-yr period 1989 to 2013. The analysis focuses on TCs that achieve gale-force (17ms21) sustained winds. Objective criteria were established to define TC tracks once they reach gale force for both observed and detected TCs. A lack of consistency between storm tracks preceding this level of intensity led these track segments to be removed from the analysis.Asubtropical jet (STJ) diagnostic is used to terminate transitioning TCs and is found to be preferable to a fixed latitude cutoff point. TC tracks were analyzed across seven TC basins, using a probabilistic clustering technique that is based on regression mixture models. The technique grouped TC tracks together based on their geographical location and shape of trajectory in five separate ‘‘cluster regions’’ around the globe. A mean trajectory was then regressed for each cluster that showed good agreement between the detected and observed tracks. Other track measures such as interannual TC days and translational speeds were also replicated to a satisfactory level, with TC days showing limited sensitivity to different latitude cutoff points. Successful validation in reanalysis data allows this model- and grid-resolution-independent TC tracking scheme to be applied to climate models with confidence in its ability to identify TC tracks in coarse-resolution climate models.
- Authors: Bell, Samuel , Chand, Savin , Tory, Kevin , Turville, Christopher
- Date: 2018
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 31, no. 6 (2018), p. 2217-2232
- Full Text:
- Reviewed:
- Description: The Okubo–Weiss–Zeta (OWZ) tropical cyclone (TC) detection scheme, which has been used to detect TCs in climate, seasonal prediction, and weather forecast models, is assessed on its ability to produce a realistic TC track climatology in the ERA-Interim product over the 25-yr period 1989 to 2013. The analysis focuses on TCs that achieve gale-force (17ms21) sustained winds. Objective criteria were established to define TC tracks once they reach gale force for both observed and detected TCs. A lack of consistency between storm tracks preceding this level of intensity led these track segments to be removed from the analysis.Asubtropical jet (STJ) diagnostic is used to terminate transitioning TCs and is found to be preferable to a fixed latitude cutoff point. TC tracks were analyzed across seven TC basins, using a probabilistic clustering technique that is based on regression mixture models. The technique grouped TC tracks together based on their geographical location and shape of trajectory in five separate ‘‘cluster regions’’ around the globe. A mean trajectory was then regressed for each cluster that showed good agreement between the detected and observed tracks. Other track measures such as interannual TC days and translational speeds were also replicated to a satisfactory level, with TC days showing limited sensitivity to different latitude cutoff points. Successful validation in reanalysis data allows this model- and grid-resolution-independent TC tracking scheme to be applied to climate models with confidence in its ability to identify TC tracks in coarse-resolution climate models.
An assessment of a model-, grid-, and basin-independent tropical cyclone detection scheme in selected CMIP3 global climate models
- Tory, Kevin, Chand, Savin, Dare, Richard, McBride, John
- Authors: Tory, Kevin , Chand, Savin , Dare, Richard , McBride, John
- Date: 2013
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 26, no. 15 (2013), p. 5508-5522
- Full Text:
- Reviewed:
- Description: A novel tropical cyclone (TC) detection technique designed for coarse-resolution models is tested and evaluated. The detector, based on the Okubo-Weiss-Zeta parameter (OWZP), is applied to a selection of Coupled Model Intercomparison Project, phase 3 (CMIP3), models [Commonwealth Scientific and Industrial Research Organisation Mark, version 3.5 (CSIRO-Mk3.5); Max Planck Institute ECHAM5 (MPI-ECHAM5); and Geophysical Fluid Dynamics Laboratory Climate Model, versions 2.0 (GFDL CM2.0) and 2.1 (GFDL CM2.1)], and the combined performance of the model and detector is assessed by comparison with observed TC climatology for the period 1970-2000. Preliminary TC frequency projections are made using the three better-performing models by comparing the detected TC climatologies between the late twentieth and late twenty-first centuries. Very reasonable TC formation climatologies were detected in CSIRO-Mk3.5, MPI-ECHAM5, and GFDL CM2.1 for most basins, with the exception of the North Atlantic, where a large un-derdetection was present in all models. The GFDL CM2.0 model was excluded from the projection study because of a systematic underdetection in all basins. The above detection problems have been reported in other published studies, which suggests model rather than detector limitations are mostly responsible. This study demonstrates that coarse-resolution climate models do in general produce TC-like circulations with realistic geographical and seasonal distributions detectable by the OWZP TC detector. The preliminary projection results are consistent with the published literature, based on higher-resolution studies, of a global reductionofTCs between about6%and 20%, withamuch larger spread of results (about 120% to 250%) in individual basins. © 2013 American Meteorological Society.
- Authors: Tory, Kevin , Chand, Savin , Dare, Richard , McBride, John
- Date: 2013
- Type: Text , Journal article
- Relation: Journal of Climate Vol. 26, no. 15 (2013), p. 5508-5522
- Full Text:
- Reviewed:
- Description: A novel tropical cyclone (TC) detection technique designed for coarse-resolution models is tested and evaluated. The detector, based on the Okubo-Weiss-Zeta parameter (OWZP), is applied to a selection of Coupled Model Intercomparison Project, phase 3 (CMIP3), models [Commonwealth Scientific and Industrial Research Organisation Mark, version 3.5 (CSIRO-Mk3.5); Max Planck Institute ECHAM5 (MPI-ECHAM5); and Geophysical Fluid Dynamics Laboratory Climate Model, versions 2.0 (GFDL CM2.0) and 2.1 (GFDL CM2.1)], and the combined performance of the model and detector is assessed by comparison with observed TC climatology for the period 1970-2000. Preliminary TC frequency projections are made using the three better-performing models by comparing the detected TC climatologies between the late twentieth and late twenty-first centuries. Very reasonable TC formation climatologies were detected in CSIRO-Mk3.5, MPI-ECHAM5, and GFDL CM2.1 for most basins, with the exception of the North Atlantic, where a large un-derdetection was present in all models. The GFDL CM2.0 model was excluded from the projection study because of a systematic underdetection in all basins. The above detection problems have been reported in other published studies, which suggests model rather than detector limitations are mostly responsible. This study demonstrates that coarse-resolution climate models do in general produce TC-like circulations with realistic geographical and seasonal distributions detectable by the OWZP TC detector. The preliminary projection results are consistent with the published literature, based on higher-resolution studies, of a global reductionofTCs between about6%and 20%, withamuch larger spread of results (about 120% to 250%) in individual basins. © 2013 American Meteorological Society.