Heat Waves

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Heat Waves
The 1995 Heat Wave How Likely is a Recurrence?
By Thomas R. Karl Richard W. Knight
Contribution of Land-Atmosphere Coupling to
Recent European Heat Waves
By Fischer, Seneviratne, Lüthi, Schär

• By Kathryn Bullinger

Double Major Geography and Earth Sciences
Kathryn Bullinger
Geography and Earth Sciences Double Major
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Lets Start with the Basics
What are they? (if the name alone isnt enough
of a clueseriously.)

• Defined It is a prolonged period of excessive
  heat, often accompanied by excessive humidity.
• Qualifications
• The weather is noticeably warmer than normal for
  the time of year and climate.
• The unusual weather continues for a prolonged
  period of time long enough to be considered a
  specific phase.
• The weather will most likely bring about some
  sort of increased risk to humans and animals, and
  may place an increased strain on power supplies.

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How Does This Happen?

• When an air mass becomes quasi-static/stationary
  over a region (and it meets all those
  qualifiers), it is labeled a heat wave.

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Why they are Dangerous

• Heat kills by taxing the body beyond its normal
  abilities.
• On average, lt 1000 Americans die heat-related
  deaths each year (as reported by the American
  Meteorological Society)
• Heat waves kill more Americans than any other
  type of natural disaster.

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Why they are Dangerous Contd.

• People who live in urban areas are at a greater
  risk from heat wave effects.
• Stagnant atmospheric conditions trap pollutants.
• Poor air quality aggravates health problems.
• Asphalt and concrete store heat longer, which
  results in higher nighttime temperatures.
• Known as the urban heat island effect.

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The Chicago Heat Wave of 95

• July 12th - 16th, 1995.
• Approximately 700 people died in just 5 days.
• July 13th
• The temperature in the city hit 106 F.
• Including the heat index, it felt hotter than
  120 F.
• Chicagos infrastructure had a meltdown (almost
  literally).
• Communities lost water pressure.
• Train rails and roads buckled.
• Paramedics, hospitals, and morgues overwhelmed.
• Majority of deaths were elderly men who lived
  alone.

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On to the 1st Paper!

• The analysis
• Considers the apparent temperature, Tap , which
  attempts to quantify the effects of temp. and
  moisture on the human body.
• Focuses on the severity and duration of extreme
  heat waves relative to changes of mean T,
  variance, day-to-day persistence of T, and the
  cross correlations of these quantities.
• Also created future scenarios for heat waves of
  similar or greater intensity.

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Notable Points that they Took into Account for
their Analysis

• High dewpoints play a key role in high Tap
  values.
• Minimum T may be especially important.
• Deaths due to heat are greatest during the 1st
  few days of a heat wave.
• Acclimatization factors also seem to be important.

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Assessing the Wave

• Use the Tap algorithm developed by Steadman.
• Tap values apply to shaded daytime conditions
  and night.
• Focus on the the full distribution of hourly Ts
  during the 1st few days for 26 stations in and
  around the Chicago area.

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Min, 25P, 50P, 75P, and Max T plotted for the
warmest annual 1, 2, and 3-day events in Chicago
history.
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Calculated the average Tap for any 2-day period
during the 95 heat wave to help delineate the
aerial extent of the wave.
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Calculating Trends of Tap

• Used values from 1, 2, and 3-day intervals
  between June 15th and August 15th (the period of
  most intense summertime heat in the Midwest).
• The analysis was performed for both observed Tap
  and those adjusted for the effects of the growth
  of the urban heat island.

• Heat island adjustments applied based on the
  algorithm developed by Karl et al.
• Used the algorithm to help develop an interval
  that would bound the effects of urbanization on
  T trends.

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Applying the Algorithm

• Assumed the hourly Ts at 1500 LT were associated
  with the max and Ts at 0600 LT with the min.
• Started with a population of 0 for each urban
  area, with the final population estimate equal to
  the 1990 city census (to provide an upper bound
  for the effect of urbanization on the trends of
  T.

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The Probability of Recurrence

• 10,000 sequences on monthly July daily max and
  min values were simulated using various values of
  a 4-parameter model.
• Mean Tap
• Sa - the variance of monthly mean Tap calculated
  across years
• Sm - the variance of Tap calculated for a given
  month using daily values
• r - persistence coefficient of the daily Tap

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• Using the simulated July values of daily max and
  min Tap, the probability of exceeding specific
  thresholds of T can be easily calculated relative
  to what actually occurred during 1995.

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Their Results
Is there a looming doomsday in our future?

• The stationarity of Tap
• The overall trends of Tap in the Midwest are more
  moderate than the Chicago results.
• However, the climate in the Midwest appears to be
  stationary.
• Sensitivity of the probabilistic model
• Changes in mean Tap are important, but other
  parameters are also critical, such as persistence
  and variance.

• Recurrence for the 95 heat wave in the present
  climate
• The probability of max Tap exceeding 48.9 C two
  consecutive days in a row is lt 1 , or 1 in 150
  years.
• The probability of having min Tap values above
  31.6 C for two consecutive days is extremely
  rare.
• Recurrence for the 95 heat wave in a changed
  climate
• Projected increases in T are by 3 C by the end
  of the next century due to greenhouse gases.
• Faster return periods for extreme Ts.

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The Sensitivity of Multivariate and Univariate
Changes
Daily max
Daily min
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Their Summary

• An event like the Chicago heat wave of 95 is
  quite rare, due to the elevated 2-day nighttime
  (min) temperatures.
• Duration and intensity of heat waves have been
  shown to be affected by 4 parameters.
• Min Tap probability results especially rare and
  unusual.
• In their opinion, and event like the Chicago heat
  wave will not be repeated any time in the near
  future.

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Guess What!? Im Not Done Yet!
Paper Number Twoomg

• Most of the recent European heat waves have been
  preceded by a spring precipitation deficit.
• Regional climate simulations conducted with and
  w/o land/atmosphere coupling for 4 major European
  heat waves 1976, 1994, 2003, and 2005.

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An Intro to European Heat Waves

• 2003 heat wave record-breaking over 40,000
  deaths.
• Crop shortages.
• Forest fires.
• These highlight the importance of understanding
  what causes these extreme events.

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The Experiment

• Focuses on Europe and the north-eastern Atlantic.
• Performs a 46-year simulation (1960-2005) with a
  coupled land-surface scheme (CL simulation).
• Repeat the simulations for 76, 94, 03, and
  05, but with soil moisture uncoupled from
  atmospheric evolution (UCL simulation).
• NHD and HWD

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The 4 Major Waves

• 1976
• Confined to northern France and southern England
• gt 35 hot days observed.
• 16-month period of precip. deficits prior.
• 1994
• Affected central Europe and parts of the
  Mediterranean.
• Somewhat weaker on the seasonal scale.

• 2003
• Record-breaking.
• Affected central Europe and the Mediterranean.
• 40-60 hot days observed.
• 2005
• Confined to the Iberian Peninsula and southern
  France.
• Heat wave most pronounced in June.

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Simulations
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What the Figures Show Us

• Based on these simulations, it can be seen that
  the NHD as well as the HWD is substantially
  reduced if the soil moisture is prescribed (or
  dictated) by climatological mean conditions (UCL
  simulations).
• T amplification through CL is stronger for daily
  max Ts than for min and mean Ts.
• CL interactions contribute to an enhanced
  diurnal T range.

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So Basically

• Each of the 4 waves was preceded by a mean
  precip. deficit of at least 4 months.
• CL simulations show excess in surface net rad.
  leading to an increase in evaporation.
• CL is found to increase mean max and min Ts over
  unusually warm summers.

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My Thoughts

• There is no eminent danger of us being fried by a
  drastic spike in summer temperatures.
• Heat waves do happen, but they are very
  infrequent.
• Lack of precipitation plays a role in hotter
  temperatures for the approaching summer.

• Future Study
• I would be curious to see if there is a
  connection to heat waves on different continents
  during the same year. I think some investigation
  into that could be interesting

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Questions?