Understanding the mechanisms of
Extreme Events
Watch a seminar recorded at the University of Chicago in October 2022. This talk highlights the different pathways whereby climate mechanisms engender extreme events as well as harness that information to improve extreme event prediction.
LaPlante, M., L. Deng, L. Dalanhese, and S.-Y. Wang, 2024: Ocean Temperatures Do Not Account for a Record-Setting Winter in the U.S. West. Atmosphere, in press (PDF)
Intermountain West's Record Snowpack in 2022-2023 Winter
The unexpected bounty of the Colorado River Basin's snowpack in the winter of 2022–2023 defied predictions, revealing the tenuous link between tropical sea temperatures and regional rainfall. As a critical water lifeline for the Western US, this season's atypical snowfall patterns underscore the prevailing role of stochastic forces on water availability. This reinforces the imperative for a multi-faceted approach to forecasting in water management strategies.
Stuivenvolt-Allen, J., S.-Y. Wang, M. LaPlante, and J.-H. Yoon, 2020: Three western pacific typhoons strengthened fire weather in the recent northwest U.S. conflagration. Geophysical Research Letters, in press (PDF)
The weather pattern that contributed to rapidly spreading fires in Oregon in early September 2020 can be traced back to an unexpected source: Typhoons in the western Pacific that ran into the Korean Peninsula within two weeks of each other. Together, Typhoon Bavi, Typhoon Maysak and Typhoon Haishen each contained enough energy to perturb the jet-stream—creating an atmospheric wave train that enhanced the hot-dry weather of western U.S. This study uses forecast models and weather observations to show that these typhoons amplified areas of high pressure and low pressure in North America leading to the intense winds which rapidly spread fire in Oregon, Washington and California.
Zhao, L., S.-Y. Wang, E. Becker, J.-H. Yoon, and A. Mukherjee, 2020: Cyclone Fani: The tug-of-war between regional warming and anthropogenic aerosol effects. Environmental Research Letters, DOI:10.1088/1748-9326/ab91e7 (PDF).
Cyclone Fani (2019) developed in the soup of aerosols over very warm Bay of Bengal water. We analyzed the compound effects of aerosols and climate warming on this tropical cyclone.
Aerosol and its interaction with rainfall suppressed Fani’s strengthening due to warming, but it could not counteract it.
Son, R., S.-Y. Wang, W.-L. Tseng, C. W. B. Schuler, E. Becker, and J.-H. Yoon, 2019: Climate diagnostics of the extreme floods in Peru during early 2017. Climate Dynamics, DOI:10.1007/s00382-019-05038-y.
An atmospheric forcing in early 2017 linked to the Trans-Niño Index initiated the local SST warming along coastal Peru that later expanded to the equator. There is a tendency towards more frequent and stronger variations in the water vapor flux convergence.
Stuivenvolt-Allen J and S-Y Wang (2019) Data Mining Climate Variability as an Indicator of U.S. Natural Gas. Front. Big Data 2:20. doi: 10.3389/fdata.2019.00020
Anomalously cold winters with extreme storms strain natural gas (NG) markets. Western Pacific sea surface temperatures and atmospheric pressure patterns describe significant variation in seasonal NG storage and consumption.
Wang, S.-Y., H. Kim, D. Coumou, J.-H. Yoon, L. Zhao, and R. R. Gillies, 2019: Consecutive extreme flooding and heat wave in Japan: Are they becoming a norm? Atmospheric Science Letters, DOI:10.1002/asl.933
Southern Japan suffered from a succession of extreme events in summer 2018. The sequential yet contrasting extreme events in Japan reflect an amplified East Asian summer monsoon lifecycle in a warmer climate.
Pokharel, B., S.-Y. Wang, J. D. D. Meyer, R. Gillies, and Y.-H. Lin, 2018: Weakly-forced yet high-impact convective storms in the Ohio River Valley and Mid-Atlantic United States. Climate Dynamics, DOI: 10.1007/s00382-018-4472-0
📙 Climate Extremes: Patterns and Mechanisms. ISBN: 978-1-119-06784-9, 400 pages, July 2017, American Geophysical Union
Although we are seeing more weather and climate extremes, individual extreme events are very diverse and generalization of trends is difficult. This volume documents various climate extreme events and associated changes that have been analyzed through diagnostics, modeling, and statistical approaches. Climate Extremes: Patterns and Mechanisms is a resource for scientists and graduate students.
Wang, S.-Y., J.-H. Yoon, E. Becker, and R. R. Gillies, 2017: California from drought to deluge. Nature Climate Change, 7, 465-468. (PDF)
The dramatic switch from drought to flooding in California, and the accompanying flip from atmospheric ridge to trough, exemplifies the pathways to an intensified water cycle under a warming climate.
Wang, S.-Y., Y.-H. Lin, M.-Y. Lee, J.-H. Yoon, J. D.D. Meyer, and P. J. Rasch, 2017: Accelerated increase in the Arctic tropospheric warming events surpassing stratospheric warming events during winter, Geophysical Research Letters, doi: 10.1002/2017GL073012
Rapid Arctic warming in the troposphere has increased leading to more intense and rapid cold periods that can impact East Asia, such as the January 2016's extreme cold.
Fosu, B., S.-Y. Wang, and J.-H. Yoon, 2016: The 2014/15 snowpack drought in Washington State and its climate forcing. Bulletin of the American Meteorological Society, DOI:10.1175/BAMS-D-16-0154.1 (PDF).
The 2014/15 snowpack drought in WA resulted from exceedingly high temperatures despite normal precipitation—a recurring drought type under climate warming aggravated by naturally driven low precipitation.
Wang, S.-Y., L. Zhao, and R. R. Gillies, 2016: Synoptic and quantitative attribution of the extreme precipitation leading to the August 2016 Louisiana flood, Geophysical Research Letters, DOI: 10.1002/2016GL071460 (PDF)
The 2016 flood in Louisiana resulted from an eastward traveling baroclinic trough to the north interacting with a slow-moving tropical low-pressure system in the Gulf Coast. This type of weather interaction may increase.
Promchote, P., S.-Y. Wang, and P. G. Johnson, 2016: The 2011 Great Flood in Thailand: Climate Diagnostics and Implications from Climate Change. Journal of Climate, 29, 367-379
Collective abnormal conditions contributed to the intensity of the Great Thailand Flood: high pre-monsoon rainfall; record-high soil moisture content; elevated sea level height in the Gulf of Thailand constraining drainage; and other water management factors.
Yoon, J.-H., Wang, S.-Y., R. R. Gillies, L. Hipps, B. Kravitz, and P. Rasch, 2015: Extreme Fire Season in California: A Glimpse into the Future?. Bulletin of the American Meteorological Society, 96, DOI: 10.1175/BAMS-D-15-00114.1 (PDF).
The fire season in northern California during 2014 was the second largest in terms of burned areas since 1996. An increase in fire risk in California is attributable to human-induced climate change.
Yoon, J.-H., Wang, S.-Y., R. R. Gillies, B. Kravitz, L. Hipps, and P. Rasch, 2015: Increasing Water Cycle Extremes in California and in Relation to ENSO Cycle Under Global Warming. Nature Communications, DOI: 10.1038/ncomms9657 (PDF).
Both intense drought and excessive flooding are projected to increase by at least 50% associated with a strengthened relation to ENSO—extreme El Niño and La Niña that modulate California's climate also through its precursor patterns.
Wang, S.-Y., B. Fosu, R. R. Gillies, and P. M. Singh, 2015: The Deadly Himalayan Snowstorm of October 2014: Synoptic Conditions and Associated Trends. Bulletin of the American Meteorological Society, 96, S89-94 (PDF).
The Himalayan snowstorm of October 2014 resulted from the unusual merger of a tropical cyclone with an upper trough. Their collective changes under climate warming have increased the odds for similar events.
Wang, S.-Y., W.-R. Huang, H.-H. Hsu, and R. R. Gillies, 2015: Role of strengthened El Nino teleconnection in the May 2015 floods over the southern Great Plains. Geophysical Research Letters, DOI: 10.1002/2015GL065211.
Anthropogenic warming contributed to the persistent precipitation in May 2015: Warming in the tropical Pacific that strengthened the teleconnection, amplified mid-latitude short waves that deepened the spring trough west of Texas, and enhanced Great Plains low-level jet increasing moisture.
Cho, C., Li, R., S.-Y. Wang, J.-H. Yoon, and R. R. Gillies, 2015: Anthropogenic footprint of climate change in the June 2013 northern India flood. Climate Dynamics, DOI: 10.1007/s00382-015-2613-2. (PDF)
Northern India has experienced increasingly large rainfall in June since 1985 associated with a tendency in the upper troposphere towards amplified short waves. The phasing of the amplified short waves is tied to increased loading of green-house gases and aerosols
Wang, S.-Y., L. Hipps, R. R. Gillies, and J.-H. Yoon, 2014: Probable causes of the abnormal ridge accompanying the 2013-14 California drought: ENSO precursor and anthropogenic warming footprint. Geophysical Research Letters. DOI: 10.1002/2014GL059748
The 2014 California drought was initiated by a high-amplitude ridge that emerged from continual sources of Rossby wave energy in the western North Pacific. The ridge induced a trough over the northeast U.S., forming a dipole that is increasingly linked with a type of ENSO precursor.
A continued water storage increase over the Missouri River Basin was observed prior to the 2011 flood; this implies persistence of dry conditions for the next 2 to 3 years, which coincided with the 2012 Midwest drought.
Buckley, B. M., R. Fletcher, S.-Y. Wang, B. Zottoli, and C. Pottier, 2014: Monsoon extremes and society over the past millennium on mainland Southeast Asia. Quaternary Science Reviews, 95, 1-19.
Southeast Asian climate was unstable from the late 14th to early 15th century, including alterations to water infrastructure to cope with drought, water damage to infrastructure that rendered it useless, and similar drought and floods impacting Vietnam.
Zhao, L., Wang, S.-Y., J. Jin and A. J. Clark, 2014: WRF model simulations of a rare springtime bow echo near the Great Salt Lake. Meteorological Applications (Royal Met. Soc.), DOI: 10.1002/met.1455.
The semiarid climate and rugged terrain in the interior west do not favor the development of bow echoes. However, on 21 April 2011, a bow echo formed across the Great Salt Lake in Utah. While the presence of GSL did not impact bow echo development, there is an increasing trend towards similar bow echoes.
Wang, S.-Y., R. E. Davies, and R. R. Gillies, 2013: Identification of extreme precipitation threat across midlatitude regions based on short-wave circulations. Journal of Geophysical Research, 118, 11059-11074 (pdf).
A circulation-based index was developed by combining (a) the CGT (short wave) and LLJ coupling, (b) the extent to which this coupling connects to regional precipitation and (c) the spatial correspondence with the CGT trend. The results suggest a link between the CGT/LLJ trends and recent extreme precipitation events.
Wang, S.-Y., R. E. Davies, W.-R. Huang, and R. R. Gillies, 2011: Pakistan’s two-stage monsoon and links with the recent climate change. Journal of Geophysical Research, 116, D16114.
In northern Pakistan, a pre-monsoon phase (with episodic and intense rainfall) and a monsoon trough phase (with persistent rainfall) comprise the summer rainfall. The extreme precipitation leading to the 2010 flood resulted from a pre-monsoon trend that promotes baroclinity.
Wang, S.-Y., L. E. Hipps, R. R. Gillies, X. Jiang, and A. L. Moller, 2010: Circumglobal teleconnection and early summer rainfall in the U.S. Intermountain West. Theor. Appl. Climatol., 102, 245-252.
The very wet spring of 2009 in the Central Intermountain West was investigated. Persistent rainy conditions were associated with a pronounced circumglobal teleconnection (CGT) with a wave-5 structure, consistent with a prevailing mode of the summer circulation anomalies.
Chen, T.-C., S.-Y. Wang, M.-C. Yen, A. J. Clark, and J.-D. Tsay, 2010: Sudden surface warming/drying events caused by typhoon passages across Taiwan. J. Appl. Meteor. Climatol., 49, 234-252.
When tropical cyclones interact with steep terrain, the damages go beyond just flood and wind. During typhoon passages, Taiwan's steep mountain range creates severe downslope warming and drying, which damages crops.
Chen, T.-C., S.-Y. Wang, and M.-C. Yen, 2007: Enhancement of afternoon thunderstorm activity by urbanization in a valley: Taipei. J. Appl. Meteor. Climatol., 46, 1324–1340.
Taipei is a metropolis surrounded by hills and mountains that form a basin in which two river valleys connect the surface airflow with the open sea. Summer rainfall in Taipei is largely produced by diurnal thunderstorms. The expanding urban and associated heat island has increased see breezes, enhancing thunderstorm activity and rainfall.