Characteristics of Extreme Heat Events in Vietnam: Statistical Overview Through Md Index and Lagrangian Analysis
Main Article Content
Abstract
Abstract: The study investigates the heat extreme events characteristics across seven subregions of Vietnam from March to September using ERA5 reanalysis data for the period 1981 – 2024. The characteristics of heatwaves are determined from the dimensionless heatwave index Md, which standardizes the exceedance level of daily maximum temperature (Tx) relative to its percentile threshold. Results reveal an increase in frequency, duration, intensity, and spatial extent, with notable regional disparities, particularly in the Northwest, Central Vietnam, Central Highlands, and Southern regions during study period. A prolonged April 2024 extreme heat event, with record coverage over the entire subregions of Vietnam, was driven by joint influence of the Bay of Bengal anticyclone and the western North Pacific subtropical anticyclone. Backward trajectory analysis (in Lagrangian methodology) revealed two air parcel origins: continental (dry, foehn-enhanced) and oceanic (humid), whose interation amplified heat intensity and scale. These findings highlight multi-mechanism drivers of extreme heat condition in Vietnam and underscore the importance of integrating synoptic and Lagrangian analyses for improved forecasting and climate adaptation.
Keywords:
Extreme heat event, heat analysis, ERA5.
References
[1] R. M. Horton, J. S. Mankin, C. Lesk, E. Coffel, C. Raymond, A Review of Recent Advances in Research on Extreme Heat Events, Current Climate Change Reports, Vol. 2, No.4, 2016, pp. 242-259, 10.1007/s40641-016-0042-x.
[2] IPCC, Annex I: Observational Products [Trewin, B. (ed.)], in Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, V. M. Delmotte, P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, B. Zhou, Editors, Cambridge University Press: Cambridge, United Kingdom and New York, NY, USA, 2021, pp. 2061-2086.
[3] G. Meehl, C. Tebaldi, More Intense, More Frequent, and Longer Lasting Heat Waves in the 21st Century, Science (New York, N.Y .), Vol. 305, No., 2004, pp. 994-997, https://doi.org/10.1126/science.1098704.
[4] T. T. Kiem, Characteristics and Main Synoptic Patterns Causing Heatwave Weather in Vietnam, Presented in Proceedings of the 5th Scientific Conference, 2000, National Center for Hydrometeorology (in Vietnamese).
[5] N. D. Ngu, Climate Change – Challenges to Development (Part 1), Environmental Economics, No. 1, 2009 (in Vietnames).
[6] L. V. Alexander, X. Zhang, T. C. Peterson, J. Caesar, B. Gleason, A. M. G. Klein Tank, M. Haylock, D. Collins, B. Trewin, F. Rahimzadeh, A. Tagipour, K. Rupa Kumar, J. Revadekar, G. Griffiths, L. Vincent, D. B. Stephenson, J. Burn, E. Aguilar, M. Brunet, M. Taylor, M. New, P. Zhai, M. Rusticucci, J. L. V. Aguirre, Global Observed Changes in Daily Climate Extremes of Temperature and Precipitation, Journal of Geophysical Research: Atmospheres, Vol. 111, No. D5, 2006, https://doi.org/10.1029/2005JD006290.
[7] W. Lass, A. Haas, J. Hinkel, C. Jaeger, Avoiding the Avoidable: Towards a European Heat Waves Risk Governance, International Journal of Disaster Risk Science, Vol. 2, 2011, pp. 1-14.
[8] L. P. Thi, H. P. Thanh, T. P. Van, Y. V. Thuan, Variability of Heatwaves Across Vietnam in Recent Decades, Vietnam Journal of Earth Sciences, Vol. 45, No. 4, 2023, pp. 517-530, https://doi.org/10.15625/2615-9783/19057.
[9] H. P. Thanh, L. P. Thi, H. Phan, A. Fink, R. V. D. Linden, T. P. Van, Heatwaves in Vietnam: Characteristics and Relationship with Large‐scale Climate Drivers, International Journal of Climatology, 2024, https://doi.org/10.1002/joc.8606.
[10] S. Russo, J. Sillmann, E. M. Fischer, Top Ten European Heatwaves Since 1950 and Their Occurrence in the Coming Decades, Environmental Research Letters, Vol. 10, No. 12, 2015, pp. 124003, https://doi.org/10.1088/1748-9326/10/12/124003.
[11] L. Schielicke, S. Pfahl, European Heatwaves in Present and Future Climate Simulations: A Lagrangian Analysis, Weather Clim. Dynam., Vol. 3, No. 4, 2022, pp. 1439-1459, https://doi.org/10.5194/wcd-3-1439-2022.
[12] J. Wang, Z. Yan, Rapid Rises in the Magnitude and Risk of Extreme Regional Heat Wave Events in China, Weather and Climate Extremes, Vol. 34, 2021, pp. 100379, https://doi.org/10.1016/j.wace.2021.100379.
[13] M. Amou, A. Gyilbag, T. Demelash, Y. Xu, Heatwaves in Kenya 1987-2016: Facts from CHIRTS High Resolution Satellite Remotely Sensed and Station Blended Temperature Dataset, Atmosphere, Vol. 12, No., 2020, pp. 37, https://doi.org/10.3390/atmos12010037.
[14] G. Zittis, P. Hadjinicolaou, M. Almazroui, E. Bucchignani, F. Driouech, K. Elrhaz, L. Kurnaz, G. Nikulin, A. Ntoumos, T. Ozturk, Y. Proestos, G. Stenchikov, Z. Rashyd, J. Lelieveld, Business-as-Usual will Lead to Super and Ultra-extreme Heatwaves in the Middle East and North Africa, NPJ Climate and Atmospheric Science, Vol. 4, 2021,
https://doi.org/10.1038/s41612-021-00178-7.
[15] Z. Dong, L. Wang, Y. Sun, T. Hu, A. Limsakul, P. Singhruck, S. Pimonsree, Heatwaves in Southeast Asia and Their Changes in a Warmer World, Earth's Future, Vol. 9, No. 7, 2021, pp. e2021EF001992, https://doi.org/10.1029/2021EF001992.
[16] X. X. Li, C. Yuan, J. Hang, Heat Wave Trends in Southeast Asia: Comparison of Results From Observation and Reanalysis Data, Geophysical Research Letters, Vol. 49, No.4, 2022, pp. e2021GL097151, https://doi.org/10.1029/2021GL097151.
[17] P. M. Hang, T, T. Dung, N. Đ. Quang, Influence of the South Asian Low and the Western North Pacific Subtropical High on the Evolution of Heatwaves in the North Central Region During 2010–2015, Journal of Meteorology and Hydrology, Vol. 674, No. 2, 2017 (in Vietnamese).
[18] N. V. Lanh, Heatwaves and their Causes in Vietnam, Journal of Meteorology and Hydrology, No. 597, 2010, pp. 8-13 (in Vietnamese).
[19] C. T. T. Huong, P. T. L. Huong, V. T. Hang, P. V. Tan, Magnitude and trend of heatwave variation in Vietnam during 1961–2007, VNU Journal of Science: Natural Sciences and Technology, Vol. 26, No. 3S, 2010, pp. 423-430 (in Vietnamese),
[20] L. A. Hai, M. V. Khiem, V. N. Linh, C. T. T. Huong, Assessment of Heatwave Characteristics in Southern Vietnam During 1991–2020 and Their Variations Under Different ENSO Phases, Journal of Climate Change Science, No. 21, 2022, https://doi.org/10.55659/2525-2496/21.65991 (in Vietnamese).
[21] S. Wu, M. Luo, R. Zhao, J. Li, P. Sun, Z. Liu, X. Wang, P. Wang, H. Zhang, Local Mechanisms for Global Daytime, Nighttime, and Compound Heatwaves, NPJ Climate and Atmospheric Science, Vol. 6, No. 1, 2023, pp. 36, https://doi.org/10.1038/s41612-023-00365-8.
[22] Y. Chen, Y. Li, An Inter-comparison of Three Heat Wave Types in China during 1961–2010: Observed Basic Features and Linear Trends, Scientific Reports, Vol. 7, No. 1, 2017, pp. 45619, https://doi.org/10.1038/srep45619.
[23] M. Luo, N. C. Lau, Z. Liu, Different Mechanisms for Daytime, Nighttime, and Compound Heatwaves in Southern China, Weather and Climate Extremes, Vol. 36, 2022, pp. 100449, https://doi.org/10.1016/j.wace.2022.100449.
[24] X. Liu, B. He, L. Guo, L. Huang, D. Chen, Similarities and Differences in the Mechanisms Causing the European Summer Heatwaves in 2003, 2010, and 2018, Earth's Future, Vol. 8, 2020, https://doi.org/10.1029/2019EF001386.
[25] Y. Tian, A. Kleidon, C. Lesk, S. Zhou, X. Luo, S. A. Ghausi, G. Wang, D. Zhong, J. Zscheischler, Characterizing Heatwaves Based on Land Surface Energy Budget, Communications Earth & Environment, Vol. 5, No. 1, 2024, pp. 617, https://doi.org/0.1038/s43247-024-01784-y.
[26] A. Mayer, V. Wirth, Two Different Perspectives on Heatwaves Within the Lagrangian Framework, Weather and Climate Dynamics, Vol. 6, No. 1, 2024, pp. 131-150, https://doi.org/10.5194/wcd-6-131-2025.
[27] M. Rothlisberger, L. Papritz, Quantifying the Physical Processes Leading to Atmospheric Hot Extremes at a Global Scale, Nature Geoscience, Vol. 16, No. 3, 2023, pp. 210-216, https://doi.org/10.1038/s41561-023-01126-1.
[28] P. Zschenderlein, A. Fink, S. Pfahl, H. Wernli, Processes Determining Heat Waves Across Different European Climates, Quarterly Journal of the Royal Meteorological Society, Vol. 145, 2019, pp. 2973-2989, https://doi.org/10.1002/qj.3599.
[29] H. Hersbach, B. Bell, P. Berrisford, S. Hirahara,
A. Horányi, J. M. Sabater, J. Nicolas, C. Peubey, R. Radu, D. Schepers, A. Simmons, C. Soci,
S. Abdalla, X. Abellan, G. Balsamo, P. Bechtold, G. Biavati, J. Bidlot, M. Bonavita, G. D. Chiara,
P. Dahlgren, D. Dee, M. Diamantakis, R. Dragani, J. Flemming, R. Forbes, M. Fuentes, A. Geer, L. Haimberger, S. Healy, R. J. Hogan, E. Hólm, M. Janisková, S. Keeley, P. Laloyaux, P. Lopez, C. Lupu, G. Radnoti, P. D. Rosnay, I. Rozum, F. Vamborg, S. Villaume, J. N. Thépaut, The ERA5 global reanalysis, Quarterly Journal of the Royal Meteorological Society, Vol. 146, No. 730, 2020, pp. 1999-2049, https://doi.org/10.1002/qj.3803.
[30] V. T. Phan, T. N. Duc, Seasonal and Interannual Variations of Surface Climate Elements over Vietnam, Climate Research, Vol. 40, No. 1, 2009, pp. 49-60, https://doi.org/10.3354/cr00824.
[31] E. M. Fischer, C. Schär, Consistent Geographical Patterns of Changes in High-impact European Heatwaves, Nature geoscience, Vol. 3, No. 6, 2010, pp. 398-403, https://doi.org/10.1038/ngeo866.
[32] S. E. Perkins, L. V. Alexander, On the Measurement of Heat Waves, Journal of Cliamte, Vol. 26, No. 13, 2013, pp. 4500-4517, https://doi.org/10.1175/JCLI-D-12-00383.1.
[33] M. G. Kendall, Rank Correlation Methods, American Journal of Operations Research, Vol. 3, No. 1A, 1948.
[34] H. B. Mann, Nonparametric Tests Against Trend, Econometrica, Vol. 13, No. 3, 1945, pp. 245-259, https://doi.org/10.2307/1907187.
[35] M. Sprenger, H. Wernli, The LAGRANTO Lagrangian Analysis Tool – Version 2.0, Geoscience Model Development, Vol. 8, No. 8, 2015, pp. 2569-2586,
https://doi.org/10.5194/gmd-8-2569-2015.
[2] IPCC, Annex I: Observational Products [Trewin, B. (ed.)], in Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, V. M. Delmotte, P. Zhai, A. Pirani, S. L. Connors, C. Péan, S. Berger, N. Caud, Y. Chen, L. Goldfarb, M. I. Gomis, M. Huang, K. Leitzell, E. Lonnoy, J. B. R. Matthews, T. K. Maycock, T. Waterfield, O. Yelekçi, R. Yu, B. Zhou, Editors, Cambridge University Press: Cambridge, United Kingdom and New York, NY, USA, 2021, pp. 2061-2086.
[3] G. Meehl, C. Tebaldi, More Intense, More Frequent, and Longer Lasting Heat Waves in the 21st Century, Science (New York, N.Y .), Vol. 305, No., 2004, pp. 994-997, https://doi.org/10.1126/science.1098704.
[4] T. T. Kiem, Characteristics and Main Synoptic Patterns Causing Heatwave Weather in Vietnam, Presented in Proceedings of the 5th Scientific Conference, 2000, National Center for Hydrometeorology (in Vietnamese).
[5] N. D. Ngu, Climate Change – Challenges to Development (Part 1), Environmental Economics, No. 1, 2009 (in Vietnames).
[6] L. V. Alexander, X. Zhang, T. C. Peterson, J. Caesar, B. Gleason, A. M. G. Klein Tank, M. Haylock, D. Collins, B. Trewin, F. Rahimzadeh, A. Tagipour, K. Rupa Kumar, J. Revadekar, G. Griffiths, L. Vincent, D. B. Stephenson, J. Burn, E. Aguilar, M. Brunet, M. Taylor, M. New, P. Zhai, M. Rusticucci, J. L. V. Aguirre, Global Observed Changes in Daily Climate Extremes of Temperature and Precipitation, Journal of Geophysical Research: Atmospheres, Vol. 111, No. D5, 2006, https://doi.org/10.1029/2005JD006290.
[7] W. Lass, A. Haas, J. Hinkel, C. Jaeger, Avoiding the Avoidable: Towards a European Heat Waves Risk Governance, International Journal of Disaster Risk Science, Vol. 2, 2011, pp. 1-14.
[8] L. P. Thi, H. P. Thanh, T. P. Van, Y. V. Thuan, Variability of Heatwaves Across Vietnam in Recent Decades, Vietnam Journal of Earth Sciences, Vol. 45, No. 4, 2023, pp. 517-530, https://doi.org/10.15625/2615-9783/19057.
[9] H. P. Thanh, L. P. Thi, H. Phan, A. Fink, R. V. D. Linden, T. P. Van, Heatwaves in Vietnam: Characteristics and Relationship with Large‐scale Climate Drivers, International Journal of Climatology, 2024, https://doi.org/10.1002/joc.8606.
[10] S. Russo, J. Sillmann, E. M. Fischer, Top Ten European Heatwaves Since 1950 and Their Occurrence in the Coming Decades, Environmental Research Letters, Vol. 10, No. 12, 2015, pp. 124003, https://doi.org/10.1088/1748-9326/10/12/124003.
[11] L. Schielicke, S. Pfahl, European Heatwaves in Present and Future Climate Simulations: A Lagrangian Analysis, Weather Clim. Dynam., Vol. 3, No. 4, 2022, pp. 1439-1459, https://doi.org/10.5194/wcd-3-1439-2022.
[12] J. Wang, Z. Yan, Rapid Rises in the Magnitude and Risk of Extreme Regional Heat Wave Events in China, Weather and Climate Extremes, Vol. 34, 2021, pp. 100379, https://doi.org/10.1016/j.wace.2021.100379.
[13] M. Amou, A. Gyilbag, T. Demelash, Y. Xu, Heatwaves in Kenya 1987-2016: Facts from CHIRTS High Resolution Satellite Remotely Sensed and Station Blended Temperature Dataset, Atmosphere, Vol. 12, No., 2020, pp. 37, https://doi.org/10.3390/atmos12010037.
[14] G. Zittis, P. Hadjinicolaou, M. Almazroui, E. Bucchignani, F. Driouech, K. Elrhaz, L. Kurnaz, G. Nikulin, A. Ntoumos, T. Ozturk, Y. Proestos, G. Stenchikov, Z. Rashyd, J. Lelieveld, Business-as-Usual will Lead to Super and Ultra-extreme Heatwaves in the Middle East and North Africa, NPJ Climate and Atmospheric Science, Vol. 4, 2021,
https://doi.org/10.1038/s41612-021-00178-7.
[15] Z. Dong, L. Wang, Y. Sun, T. Hu, A. Limsakul, P. Singhruck, S. Pimonsree, Heatwaves in Southeast Asia and Their Changes in a Warmer World, Earth's Future, Vol. 9, No. 7, 2021, pp. e2021EF001992, https://doi.org/10.1029/2021EF001992.
[16] X. X. Li, C. Yuan, J. Hang, Heat Wave Trends in Southeast Asia: Comparison of Results From Observation and Reanalysis Data, Geophysical Research Letters, Vol. 49, No.4, 2022, pp. e2021GL097151, https://doi.org/10.1029/2021GL097151.
[17] P. M. Hang, T, T. Dung, N. Đ. Quang, Influence of the South Asian Low and the Western North Pacific Subtropical High on the Evolution of Heatwaves in the North Central Region During 2010–2015, Journal of Meteorology and Hydrology, Vol. 674, No. 2, 2017 (in Vietnamese).
[18] N. V. Lanh, Heatwaves and their Causes in Vietnam, Journal of Meteorology and Hydrology, No. 597, 2010, pp. 8-13 (in Vietnamese).
[19] C. T. T. Huong, P. T. L. Huong, V. T. Hang, P. V. Tan, Magnitude and trend of heatwave variation in Vietnam during 1961–2007, VNU Journal of Science: Natural Sciences and Technology, Vol. 26, No. 3S, 2010, pp. 423-430 (in Vietnamese),
[20] L. A. Hai, M. V. Khiem, V. N. Linh, C. T. T. Huong, Assessment of Heatwave Characteristics in Southern Vietnam During 1991–2020 and Their Variations Under Different ENSO Phases, Journal of Climate Change Science, No. 21, 2022, https://doi.org/10.55659/2525-2496/21.65991 (in Vietnamese).
[21] S. Wu, M. Luo, R. Zhao, J. Li, P. Sun, Z. Liu, X. Wang, P. Wang, H. Zhang, Local Mechanisms for Global Daytime, Nighttime, and Compound Heatwaves, NPJ Climate and Atmospheric Science, Vol. 6, No. 1, 2023, pp. 36, https://doi.org/10.1038/s41612-023-00365-8.
[22] Y. Chen, Y. Li, An Inter-comparison of Three Heat Wave Types in China during 1961–2010: Observed Basic Features and Linear Trends, Scientific Reports, Vol. 7, No. 1, 2017, pp. 45619, https://doi.org/10.1038/srep45619.
[23] M. Luo, N. C. Lau, Z. Liu, Different Mechanisms for Daytime, Nighttime, and Compound Heatwaves in Southern China, Weather and Climate Extremes, Vol. 36, 2022, pp. 100449, https://doi.org/10.1016/j.wace.2022.100449.
[24] X. Liu, B. He, L. Guo, L. Huang, D. Chen, Similarities and Differences in the Mechanisms Causing the European Summer Heatwaves in 2003, 2010, and 2018, Earth's Future, Vol. 8, 2020, https://doi.org/10.1029/2019EF001386.
[25] Y. Tian, A. Kleidon, C. Lesk, S. Zhou, X. Luo, S. A. Ghausi, G. Wang, D. Zhong, J. Zscheischler, Characterizing Heatwaves Based on Land Surface Energy Budget, Communications Earth & Environment, Vol. 5, No. 1, 2024, pp. 617, https://doi.org/0.1038/s43247-024-01784-y.
[26] A. Mayer, V. Wirth, Two Different Perspectives on Heatwaves Within the Lagrangian Framework, Weather and Climate Dynamics, Vol. 6, No. 1, 2024, pp. 131-150, https://doi.org/10.5194/wcd-6-131-2025.
[27] M. Rothlisberger, L. Papritz, Quantifying the Physical Processes Leading to Atmospheric Hot Extremes at a Global Scale, Nature Geoscience, Vol. 16, No. 3, 2023, pp. 210-216, https://doi.org/10.1038/s41561-023-01126-1.
[28] P. Zschenderlein, A. Fink, S. Pfahl, H. Wernli, Processes Determining Heat Waves Across Different European Climates, Quarterly Journal of the Royal Meteorological Society, Vol. 145, 2019, pp. 2973-2989, https://doi.org/10.1002/qj.3599.
[29] H. Hersbach, B. Bell, P. Berrisford, S. Hirahara,
A. Horányi, J. M. Sabater, J. Nicolas, C. Peubey, R. Radu, D. Schepers, A. Simmons, C. Soci,
S. Abdalla, X. Abellan, G. Balsamo, P. Bechtold, G. Biavati, J. Bidlot, M. Bonavita, G. D. Chiara,
P. Dahlgren, D. Dee, M. Diamantakis, R. Dragani, J. Flemming, R. Forbes, M. Fuentes, A. Geer, L. Haimberger, S. Healy, R. J. Hogan, E. Hólm, M. Janisková, S. Keeley, P. Laloyaux, P. Lopez, C. Lupu, G. Radnoti, P. D. Rosnay, I. Rozum, F. Vamborg, S. Villaume, J. N. Thépaut, The ERA5 global reanalysis, Quarterly Journal of the Royal Meteorological Society, Vol. 146, No. 730, 2020, pp. 1999-2049, https://doi.org/10.1002/qj.3803.
[30] V. T. Phan, T. N. Duc, Seasonal and Interannual Variations of Surface Climate Elements over Vietnam, Climate Research, Vol. 40, No. 1, 2009, pp. 49-60, https://doi.org/10.3354/cr00824.
[31] E. M. Fischer, C. Schär, Consistent Geographical Patterns of Changes in High-impact European Heatwaves, Nature geoscience, Vol. 3, No. 6, 2010, pp. 398-403, https://doi.org/10.1038/ngeo866.
[32] S. E. Perkins, L. V. Alexander, On the Measurement of Heat Waves, Journal of Cliamte, Vol. 26, No. 13, 2013, pp. 4500-4517, https://doi.org/10.1175/JCLI-D-12-00383.1.
[33] M. G. Kendall, Rank Correlation Methods, American Journal of Operations Research, Vol. 3, No. 1A, 1948.
[34] H. B. Mann, Nonparametric Tests Against Trend, Econometrica, Vol. 13, No. 3, 1945, pp. 245-259, https://doi.org/10.2307/1907187.
[35] M. Sprenger, H. Wernli, The LAGRANTO Lagrangian Analysis Tool – Version 2.0, Geoscience Model Development, Vol. 8, No. 8, 2015, pp. 2569-2586,
https://doi.org/10.5194/gmd-8-2569-2015.