Tropical cyclones and Weather extremes - Today and in the Future - Greg Holland () - Willis Towers Watson
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Tropical cyclones c3we.ucar.edu
and Weather extremes –
Today and in the Future
Greg Holland
(gholland@ucar.edu)
Supported by NSF, Willis Re, IAG, and Zurich Insurance
1
Topics
• State of the Climate and its Impact on Weather Extremes
• Weather Extremes
• Heatwaves, Droughts, Flood Rains, Hail, Wildfires
• Changing El Nino Impacts
• Tropical Cyclones
• Recent Activity Highlights
• Increasing Losses
• Clustering
• Extreme Rainfall
• The NCAR Risk Ecosystem
Holland Willis 2018 2
State of the Climate
Global warming
1.0
• Now ~1oC and higher over land
• 1.5oC will almost certainly be passed
• Planning should be on the basis of 2oC
Attribution of Weather Extremes
• Rapidly increasing frequency of
studies on attribution
• Improving understanding and capacity
to define current and future changes
1880 1960 2020
Comprehensive information for the globe and subregions:
https://www.ametsoc.net/sotc2017/StateoftheClimate2017_lowres.pdf
Holland Willis 2018 3
Land Anomalies Already Exceed 2oC
July 2018
A recent study has shown
that the probability that the
globe will exceed 1.5oC over
the next five years is:
• 10% for a full year
• 38% or one month.
(Smith et al 2018)
https://data.giss.nasa.gov/gistemp/maps/
Holland Willis 2018 4
Climate Impact on Extremes
Extremes react strongly to relatively small
changes in the mean state.
50 %
Probability
33 %
0 1 2 3
Northern Hemisphere Temperature Anomaly (oC)
Holland Willis 2018 5
Decadal Land Temperature Trends
(Hansen et al 2012)
0 1 2
oC
Holland Willis 2018 6
Some 1oC Global Change Impacts
• Increasing Trend in:
• Severe Droughts
• Extreme Rainfall (examples later)
• Heat Waves: 10-20% of land mass exceeds previous record
• Polar Lows: Small decreasing trend in number, possible shift towards Scandinavia
• Medicanes: Possible increase in west, decrease in east
• Extratropical Cyclones:
• Increasing rainfall
• Little change in intensity
• Small potential increase in windstorm damage
• Possible shift southward from Scandinavia to UK and Central Europe
• Possible increased clustering of extreme storms.
Holland Willis 2018 7
Derived Large Hail Climatology
Derived climatology
of hail >2.5 cm
diameter using an
algorithm applied to
ERA Reanalysis.
Period 1979-2011
(Prein and Holland 2018)
Data Available at
Large Hail Days per Year
https://doi.pangaea.de/10.1594/PANGAEA.893160
Holland Willis 2018 8
Large Hail Trends 1980-2016
Increasing: Central US,
Central Canada, Central
Europe (significant)
Steady: China, Eastern
Australia
Decreasing: South America,
US Eastern Rockies
Holland Willis 2018 9
El Nino and La Nina Climate Response
“an El Niño of a given
magnitude that
forms in the future is
likely to have more
influence over our
weather than if the
same El Niño formed
50 years ago.” Fusillo
et al (2018)
(http://www.greenreport.it/news/agricoltura/onu-60-milioni-persone-colpite-el-nino-
ora-misure-preventive-la-nina/
Holland Willis 2018 10ENSO Impacts on Temp. and Fire
Temperature (oC/oC) Wildfire %/oC
Anthropogenic Climate Change produces
systematic increases in the strength of
ENSO teleconnections.
Stronger teleconnection (higher
interannual variability) in red, weaker in
+30-50%
blue/green
% indicates increases in interannual
+100%
variability
Californian precipitation also has a strong
relationship with climate change (not
shown).
(Fasullo et al 2018
https://www.dropbox.com/sh/z48vgivmngb31ko/AAD8ONoxygCgZ
dwWApiI-MW-a?dl=0 )
Holland Willis 2018 11Tropical Cyclones
Typhoon Jebi, Japan
Jebi:
• Was the most
intense to hit Japan
since 1993
• Preconditioned the
soil with moisture
for the subsequent
quake-initiated
mudslides.
Holland Willis 2018 122017-18 Season Summary
2018
2018
2017-18
(Reynoso 2018)
Holland Willis 2018 13The Global Record Breakers: 2018
• Gita: Most intense to hit Tonga
• Lane: Wettest in Hawaii, 2nd wettest in US after Harvey
• Walaka: 2nd most intense in Central Pacific
• Michael: Strongest to hit the Florida Panhandle, loss of life and
damage well over land
• Jebi: Strongest to hit Japan since 1993.
• Marcus: Strongest to hit Darwin since 1974
• Yutu: 10th Cat 5 cyclone for 2018 and 5th most intense landfalling
cyclone on record.
Five Cat 4+ hurricanes have hit US and its territories since
August 2017. Previous record - two cat 4’s in two years.
Holland Willis 2018 14Global Tropical Cyclone Trends/oC
• Frequency: Nil or slight decrease, poleward expansion is
occurring
• Maximum possible intensity: Increasing 5-10%
• Intensity Distribution: Substantial increase in proportion of Cat
4 and 5, total climate impact may have already occurred
• Landfall Intensity: Seven of the 10 most intense landfalls on
record have occurred since 2006
• Storm Surge: Doubling in probability, especially for extreme
surges
• Rainfall: 5-10% increase overall, possible substantial increase in
extremes.
Holland Willis 2018 15Changes in Hurricane Losses %/oC
(Ranson et al 2014)
Holland Willis 2018 16Extreme Cyclone Rainfall: Debbie
• Category 4
• US$2.7B Damage
• 14 deaths
Almost all from severe and record
flooding (up to 1300 mm) south of
the landfall location.
Local ocean temperatures ~2oC
above preindustrial levels.
Holland Willis 2018 17Hybrid WRF Cyclone Model
Pre-Industrial Current (+1oC) Future (+2oC)
Pre-Industrial Climate Change Debbie closely
Intensity -13% +12% followed the 2oC
Cyclone Damage Potential -25% +12% simulation in both
Total Precipitation -32% +100% track and rainfall.
Rain rate / intensity -12% +150%
Holland Willis 2018 18Extreme Cyclone Rainfall: Harvey
• Category 4
• US$125B Damage
• 107 deaths
Almost all from severe and record
flooding (up to 1000mm) around and
east of the landfall location.
Moisture came from local evaporation
of anomalously-warm Gulf waters
(Trenberth et al 2018)
Holland Willis 2018 19Real Time Hurricane Attribution
Current Climate Climate Change Removed
Real-time attribution
of climate change
impacts on rainfall
for Hurricane
Florence.
(https://cpb-us-
e1.wpmucdn.com/you.stonybrook.edu/dist/4/945/files/2018/09/09102018
00_Florence-one-pager-2lsrl7n.pdf )
Holland Willis 2018 20Clustering of Weather Extremes
Note that clustering impacts may arise from:
• Two or more extremes in spatial or temporal proximity
• Several relatively minor events that provide conditions for a latter
system to become disastrous.
21
Holland Willis 2018Why do Storms Cluster?
• Stochastic – Unpredictable?
• Environmental – Predictable?
• Combining the Two may Provide Predictable Elements
Holland Willis 2018 22A Thought Experiment
Chance of rolling two sixes, P=1/36
• Weight the dice, P>1/36 More favourable
intensification environment
• Roll 10 times, P~0.5 More intense hurricanes in
a season
Increased proportion of
• Turn the 1’s into 6’s, P=1/9
Cat4/5 hurricanes
• Combine two or more of Impact of climate change.
above
Add in the increases in exposed populations and infrastructure!
Holland Willis 2018 23e.g. Multiple US Cat 3+ Landfalls
2MH 3MH 2MH 3MH
>1/200 >1/200 1/25 >1/200
(>1/200) (>1/200) (1/25) (>1/200) Past 30 y
(Future)
Current risk
lies
2MH 3MH 2MH 3MH between
1/40 >1/200 1/15 >1/60 these.
(1/20) (1/180) (1/7) (>1/30)
(Kossin et al 2010; Papachristou and Duan 2018)
Holland Willis 2018 24SST Anomaly by Group
(Kossin et al 2010)
Holland Willis 2018 25September 2017 SST Anomaly
Favours Clusters 3 and 4
• 2 MH P~10%
• 3 MH P=2-3%
First recorded Landfall of
two Cat 4 Hurricanes -
Harvey (Aug) and Irma (Sep,
both from Cluster 3)
Four Cat 4 hurricane
landfalls in 14 months!
Holland Willis 2018 26But For 2017 Let Us Add
• Low vertical windshear
• Environmental flow that holds TCs on long E-W trajectory
• Very high SST in western Caribbean
• Irma: 2nd most intense Atlantic Hurricane; longest time
>=160 kt; most intense ever in Leeward Islands
• Climate increases in proportion of Cat 4/5 hurricanes.
Perhaps we are able to provide useful information on the likelihood and
character of clustering from both stochastic and predictable elements.
The question remains on how much weather-extreme clustering cascades
down to clustered losses.
Holland Willis 2018 27NCAR Risk Ecosystem
Stochastic Modules 50 m/s 10-y Wind
• Adaptation of Geoscience Australia TCRM Return Period
• Rain, Hail, etc Based on Climate Model Ensembles
TC Wind and Rain
Footprint Modules
• Hybrid WRF
• Boundary-layer Model
Rain Surface Wind
0.30
April 1 Forecast
July 1 Forecast
Historical
Likelihood
Impact Modules
0.20
0.10
0.00
flag
0 2 4 6 8 10 12
CDP
Cyclone Damage Potential
Holland Willis 2018 28Willis Global Wind Footprint
Next Presentation
Holland Willis 2018 29Repechage
Extremes react strongly to relatively small
changes in the mean state.
Probability
33 %
0 1 2 3
Northern Hemisphere Temperature Anomaly (oC)
• The climate has warmed by 1oC
• We already are experiencing associated increases in extremes - for
weather systems, clustering, and related damages.
Holland Willis 2018 30You can also read
