AMERICAN METEOROLOGICAL SOCIETY Bulletin of the American Meteorological Society
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Understanding the drivers of variability in Severe Convection: Bringing
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together the scientific and insurance communities.
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John T. Allen∗
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Department of Earth and Atmospheric Sciences, Central Michigan University, Mt Pleasant,
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Michigan, USA.
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International Research Institute for Climate and Society, Columbia University, Palisades, New
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York, USA.
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Michael K. Tippett
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Department of Applied Physics and Applied Mathematics, Columbia University, New York, New
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York, USA.
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Center of Excellence for Climate Change Research, Department of Meteorology, King Abdulaziz
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University, Jeddah, Saudi Arabia.
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Adam H. Sobel
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Department of Applied Physics and Applied Mathematics and
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Department of Earth and Environmental Sciences, Columbia University, New York, New York,
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USA.
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Chiara Lepore
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Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA.
Generated using v4.3.2 of the AMS LATEX template
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∗ Corresponding author address: Brooks 326, Central Michigan University, Mt Pleasant, MI, 48858
E-mail:
[email protected]
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ABSTRACT 21
SUMMARY BOX
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SevCon16: 2nd Severe Convection & Climate Workshop 2016
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What: Over 110 registered participants from the academic, operational me-
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teorology and insurance sectors met to discuss the latest research in severe
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convective storms and how they are influenced by the climate system.
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When: 9 to 10 March 2016
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Where: Columbia University, New York, USA.
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1. Content
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What is our current understanding of the drivers of year-to-year variations in severe
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thunderstorms over the United States and how might a warming climate impact the risks
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associated with tornadoes and hail?
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ing their importance to both the public sector and the insurance industry, were the fo-
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cus of the 2nd Severe Convection and Climate Workshop on the 9-10th March 2016
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(http://extremeweather.columbia.edu/events/severeconvection2016/), organized by the Initiative
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on Extreme Weather and Climate at Columbia University. The workshop brought together over
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110 researchers from China, Europe and North America, reflecting a diverse spectrum of interests
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and experience, from graduate students through to senior scientists and tenured faculty.
These fundamental questions, along with assess-
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The understanding of severe thunderstorm variability is still in its infancy (Tippett et al. 2015).
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Engagement of stakeholders is critical to ensuring the questions relevant to the community are be-
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ing asked. This meeting included representatives from both the climate and severe storms commu-
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nities hailing from the academic sector, operational meteorologists, emergency managers, reinsur-
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ers, insurers and catastrophe modelers. This in turn allowed a broad perspective on the importance
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of modulations to severe thunderstorm occurrence as a response to subseasonal signals such as
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the Madden-Julian Oscillation (e.g., Barrett and Gensini 2013) and the Global Wind Oscillation
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(GWO Gensini and Marinaro 2015), seasonal climate signals such as the El Ni˜no Southern Oscil-
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lation (ENSO; e.g., Allen et al. 2015), and the impacts of a warming climate (e.g., Diffenbaugh
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et al. 2013). Spatial, magnitude and frequency modulations can have a considerable influence
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on the potential for insured losses (e.g., Sander et al. 2013), and thus ensuring the latest state of
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knowledge is communicated between the various sectors has important implications for the insur-
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ance industry and assessing public risk. Furthermore, bringing this wide ranging group together
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provided the impetus to discuss the operating procedure and understanding of insurers, reinsurers
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and catastrophe modelers, and showcasing the most recent research in the academic community.
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A key question going into and during the workshop was the degree to which information on
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prediction or even understanding of severe thunderstorm activity on subseasonal to seasonal scales
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and its response to a warming climate could be applied in the insurance industry. While workshop
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participants were unable to draw a conclusive answer to this question, discussions suggested that
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such work is of interest to the insurance sector, provided it can be determined with sufficient lead
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time to influence business decisions or risk mitigation. Despite this challenge, it was agreed that
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information on the drivers of variability were posed to effect changes to the catastrophe models,
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and potentially better inform insurance decisions in the years to come.
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The workshop opened with a session on observed severe thunderstorm events and climatology,
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highlighting new approaches for determining hail risk in Europe, including deriving hail swathes
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from favorable environmental conditions and satellite detected overshooting top data. Other top-
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ics included the increase in the number of tornadoes occurring during tornado outbreaks, a multi-
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national multi-language reanalysis of historical tornadoes in Europe, and exploration of the precur-
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sors to Derecho occurrence in the United States. The next session focused on the primary drivers
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to seasonal to subseasonal variability, including an interesting result that is highly indicative of
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tornadoes being thermophobic, or at the very least subject to a goldilocks type problem of the tem-
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perature being just right in the spring and summer for tornadoes to occur. An interesting point of
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contention arose between the below average spring (March, April, May) seasonal outlook for hail
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and tornado occurrence over the United States based on ENSO contrasting subseasonal indications
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using the GWO for an active March. This raised the issue of how to handle contrasting forecasts
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of subseasonal variability despite contributions from seasonal signals.
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The afternoon took on a different complexion, with a gentle introduction to (re)insurance that
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touched on the problems faced by insurers in dealing with the relatively long intervals between
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major severe thunderstorm driven loss events. This situation can lead to insufficient reinsurance to
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protect against catastrophic losses by local companies, which can lead to collapse of these compa-
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nies and policyholders being left out in the cold. Challenges also include a poor understanding of
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the climatological risk and ensuring that appropriate reinsurance and capital is in place to handle
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multiple catastrophic or even cumulative loss years (e.g., the 2011 tornado season). Presentations
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on the various catastrophe models followed, including an introduction as to how they are derived,
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and different approaches into estimating loss risk based on exposure. The panel that followed
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touched on one of the more interesting workshop discussions: what is the co-occurrence of severe
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thunderstorm loss events, or how do these events co-relate to landfalling Atlantic hurricanes, for
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example. Other lively discussion explored the limitations and differences between existing models
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and whether climate variability should be introduced. The evening poster session showcased an
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impressive array of graduate, undergraduate and exploratory research discussing everything from
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the sensitivity of high resolution storm simulations to aerosols to assess the recent downward trend
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in hail occurrence over China and high resolution dynamical downscaling of severe thunderstorm
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environments, as well as different approaches to determine climatological risk and assessing the
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impacts of soil moisture and the Gulf of Mexico on severe thunderstorm activity to the impact of
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various climate signals on seasonal forecasts for severe weather.
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The second day of the workshop focused on the understanding of the implications of climate
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change, storm dynamics and the less thought of precipitation and lightning risks. A notable fea-
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ture in the first session included a fascinating numerical simulation experiment that explored the
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sensitivity of recent severe thunderstorm events to the influence of a warmed climate, revealing
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that increasing convective inhibition would generally result in fewer storms, but that when storms 6
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did form, the contributions from instability would lead to greater vertical velocity. This was ac-
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companied by the latest research on the response of CAPE to global warming, changes to severe
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thunderstorms over Europe under a warming climate and continual decreasing trends in hail oc-
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currence in China. The conversation shifted to higher resolution, to what we know about tornadic
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formation, approaches to observing lightning and the new development of long-term records of
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satellite-derived observations of severe storms, and the potential for these datasets to be applied to
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climate problems. The final session of the workshop featured presentations on the long-range pre-
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dictability of precipitation extremes using the Climate Forecast System version 2, and was rounded
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out by evidence of seasonal predictability for lighting activity over Venezuela.
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Critical themes derived from the proceedings include the need for greater scrutiny of the ob-
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served datasets to identify superior climatologies of severe thunderstorms, the search for further
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predictors of severe thunderstorm variability, particularly when ENSO is not the driving influence,
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and the need to consider the potential for the clustering of risk from severe thunderstorm events
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and exposure.
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The
first
workshop
on
Severe
Convection
and was
a
Climate
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(http://wiki.iri.columbia.edu/index.php?n=Climate.TornadoWorkshop)
small
event
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in March 2013, which was the first effort to bring together both the climate and severe
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storms community.
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the influence of climate variability on severe thunderstorm events and seasonal prediction
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(http://iri.columbia.edu/news/wheres-my-seasonal-tornado-forecast/). The growth of this field
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in the intervening three years speaks to the importance of bringing together cross-disciplinary
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groups at the early stages of development for new research directions.
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meant that the second workshop doubled in size compared to the first and now includes
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a strong representation from the insurance industry along with a growing number of stu-
This workshop contributed to the beginning of the discussion about
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The growth has
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dent and early career researchers.
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made available at the workshops website for interested parties that were unable to attend
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(http://extremeweather.columbia.edu/events/severeconvection2016/).
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tions between those from the insurance and academic sectors, it is hoped that this workshop will
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continue to foster future collaboration between these groups, along with growth in the research
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community to help mitigate risk and better understand the differences between and challenges of
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years with high and low severe thunderstorm occurrence. To revisit a final point from the 2013
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meeting ”Where is my seasonal tornado forecast?”, our question following the 2016 workshop
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has now changed to ”What is our seasonal tornado forecast, how can we improve on it, and how
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can this information be used?”
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Acknowledgments. The organizers acknowledge the support for the workshop from the National
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Science Foundation, the Willis Research Network, Munich Re and the Columbia University Ini-
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tiative on Extreme Weather and Climate.
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References
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Allen, J. T., M. K. Tippett, and A. H. Sobel, 2015: Influence of the El Nino/Southern Oscillation
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Presentations and posters from the meeting have been
With productive interac-
on tornado and hail frequency in the United States. Nat. Geosci, 8, 278–283.
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Barrett, B. S. and V. A. Gensini, 2013: Variability of central United States April–May tornado
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day likelihood by phase of the Madden-Julian Oscillation. Geophys. Res. Lett., 40, 2790–2795.
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doi:10.1002/grl.50522.
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Diffenbaugh, N. S., M. Scherer, and R. J. Trapp, 2013: Robust increases in severe thunderstorm
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environments in response to greenhouse forcing. Proc. Natl. Acad. Sci. (USA), 101, 16361—
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16366. doi:10.1073/pnas.1307758110. 8
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Gensini, V. A. and A. Marinaro, 2015: Tornado frequency in the United States related to global
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relative angular momentum. Mon. Wea. Rev., 144, 801–810. doi:http://dx.doi.org/10.1175/
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MWR-D-15-0289.1.
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Sander, J., J. F. Eichner, E. Faust, and M. Steuer, 2013: Rising Variability in Thunderstorm-
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Related U.S. Losses as a Reflection of Changes in Large-Scale Thunderstorm Forcing. Wea.
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