Climate change futures: health, ecological and economic dimensions

APPENDIX B.
ADDITIONAL FINDINGS AND METHODS FOR US ANALOG STUDIES OF HEAT WAVES
This appendix covers the details of the heat wave case study and the methods used to carry out the analog studies
for five US cities.
Maximum and minimum temperatures are equally important in understanding the oppressive nature of the heat
wave during the analog summer. For 24 days nighttime temperatures tie or break high minimum temperature
records, and for 11 days they tie or break the all-time high minimum temperature record of 28°C (82°F). Eight of
the 11 days are consecutive, and such a string would undoubtedly have a very negative impact on the population
of the city.
In Washington, DC, 11 days record maximum temperatures at or above 41°C (105°F). However, the most
intense heat for the analog summer occurs in St. Louis, where an all-time maximum temperature record of 46°C
(116°F) is achieved on July 14 plus 8 days record temperatures of 44°C (110°F) or higher. Some minimum temperatures
never fall below 32°C (90°F), and an all-time high minimum temperature record of 34°C (93°F) is set
on August 9 in St. Louis.
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The normally cooler cities of New York City and Detroit are not spared in the analog event. For New York, four
days break the all-time maximum temperature record and two days achieve the same for minimums. One day
reaches 44°C (110°F) and 11 straight days in August have minimums exceeding 27°C (80°F). Detroit breaks
two all-time maximums, and has a string of seven out of eight days breaking all-time minimums. Fourteen days in
Detroit exceed 38°C (100°F) during the analog summer, including a nine-day consecutive string in August.
Methods
First, the Paris event is characterized statistically, and these characteristics are transferred to the selected US cities.
Second, the hypothetical meteorological data-set for each city is converted into a daily air mass calendar through
use of the spatial synoptic classification. A large body of literature suggests that humans respond negatively to certain
“offensive air masses,” which envelop the body during stressful conditions (Kalkstein et al. 1996; Sheridan
and Kalkstein 2004). Rather than responding to individual weather elements, we are affected by the simultaneous
impact of a much larger suite of meteorological conditions that constitute an air mass.
The spatial synoptic classifications are based on measurements of temperature, dew point temperature, pressure,
wind speed and direction, and cloud cover to classify the weather for a given day into one of a series of predetermined,
readily identifiable, air mass categories. They are:
1. Dry Polar (DP) 5. Moist Moderate (MM)
2. Dry Moderate (DM) 6. Moist Tropical (MT)
3. Dry Tropical (DT) 7. Moist Tropical Plus (MT+)
4. Moist Polar (MP)
An evaluation of the air mass frequencies for the analogs to the 2003 Paris heat wave in the five US cities provides
a clear picture of how exceptional this event would be (Table B.1). On average, Philadelphia, for example,
experiences offensive air masses MT+ or DT in June, July, and August, 15.2%, 16.5%, and 11.3% of the time,
respectively (or 14.3% averaged over the three-month summer period). Applying the 2003 analog to
Philadelphia, these values increase to 50%, 38.7% and 58%, respectively.