The Philadelphia, Pennsylvania, Hot Weather-Health Watch/Warning System was initiated in 1995 to alert the city's population to take precautionary actions when hot weather posed risks to health. The number of lives saved and the economic benefit of this system were estimated using data from 1995 to 1998. Excess mortality in people 65 yr of age and older was defined as reported mortality minus mortality predicted by a historical trend line developed over the period of 1964–88. Excess mortality during heat waves was explained using multiple linear regression. Two variables were convincingly associated with mortality: the time of season when a particular heat wave started, and a warning variable indicating whether or not a heat wave warning had been issued. The estimated coefficient of the warning variable was about −2.6, suggesting that when a warning was issued, 2.6 lives were saved, on average, for each warning day and for 3 days after the warning ended. Given the number of warnings issued over the 3-yr period, the system saved an estimated 117 lives. Estimated dollar costs for running the system were small compared with estimates of the value of a life.

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Exponent, Alexandria, Virginia

Teisberg Associates, Charlottesville, Virginia

Center for Climatic Research, University of Delaware, Newark, Delaware

Deputy Health Commissioner, City of Philadelphia, Philadelphia, Pennsylvania

Office of Policy and Strategic Planning, NOAA, Washington, D.C.