University of Delaware
Office of Public Relations
The Messenger
Vol. 5, No. 1/1995
Weather alert! Researcher's system in use in Philadelphia

     A hot weather alert system developed by a University of
Delaware professor now warns Philadelphia residents when high
temperatures may become life threatening, and it soon will be in
use in other U.S. cities.
     Developed by Laurence Kalkstein, professor of geography in
the UD Center for Climatic Research, the system is sponsored by
the Environmental Protection Agency. Based on research that
identifies the weather conditions that produce statistically
significant increases in average daily mortality, the system was
adopted last summer by Philadelphia's health department.
     Designed to provide the public with greater advance warning
of dangerous heat, the new three-tiered, computerized system
consists of a Hot Weather Health Watch, a Hot Weather Health
Alert and a Hot Weather Health Warning. While all will be issued
by Philadelphia's health commissioner, a Hot Weather Health
Warning will be released in consultation with the National
Weather Service.
     During the heat wave of June 1993, the Philadelphia Medical
Examiner's Office recorded 118 heat-related deaths.
     Prior hot weather warnings were issued by the health
department in conjunction with the National Weather Service
forecast of two consecutive days of a heat and humidity index of
105 degrees or more for at least three hours each day. These
warnings were based upon a subjective "comfort level," not
medical evidence.
     According to Kalkstein, "There is no established scientific
relationship between 105 degrees and human health. An advantage
of the new health watch/warning system for Philadelphia is the
identification of high-risk air masses that are actually
associated with elevated mortality in the summer. In addition, by
using National Weather Service forecast data for upcoming days,
it will be possible to predict the arrival of a high-risk air
mass up to two days before its arrival."
     The new system identifies a high-risk air mass through
computerized analysis of National Weather Service prediction
data. When such an air mass is detected, its impact on people is
determined based upon a formula that includes the variables of
temperature, time of year and length of a given hot spell.
     Derived from a study of 20 years of weather and mortality
statistics, the formula predicts when potentially deadly heat
will arrive in the Delaware Valley.
     Kalkstein's research has demonstrated that different regions
of the country are affected differently by the weather. Heat is
linked to an increase in deaths in cities such as Philadelphia,
Boston and New York, but not in Dallas and New Orleans, where the
climate produces less dramatic changes in weather. The system
introduced in Philadelphia is the first of its kind, and
researchers expect it will serve as a model for other cities.
                         -Ed Okonowicz, Delaware '69, '84 M