The feasibility of an evaporative cooler warning system for the U.S. Southwest

In spring, 2001, the Phoenix National Weather Service Forecast Office (WFO) began implementation of a state-of-the-art heat/health warning system for the metropolitan area. They system, developed at the University of Delaware's Center for Climatic Research, represents a great improvement over traditional NWS heat-related watches and warnings. First, it is based on actual weather-health relationships that exist in Phoenix, and advisories and warnings are called when weather conditions exceed meteorological thresholds that have historically led to increased deaths in the Phoenix area. Second, the system is based on the forecasting of "oppressive air masses," rather than just heat and humidity, which permits a broader evaluation of the meteorological conditions that lead to deteriorating health.

In 2001, we contracted by the US EPA to determine if the local Native American communities seem to be disproportionately impacted by the effects of extreme heat. A report was produced which strongly suggested that this was true; blacks and Native Americans in the Phoenix area show heat-related mortality increases that are 11 to 26 percent higher than the rest of the population. This increase rises to 20 to 36 percent when considering people 65 years and older. The reasons for this increase are unclear, but it has been suggested that the lesser availability of air conditioning, and the increased use of swamp coolers among the generally poorer population, may play some role in these disparities. One reason for this belief is that finding that, among minority populations, many of the deaths occurred late in the summer, when the Arizona monsoon was evident (most tropical air masses present). Most of the local population shows increased mortality early in the summer when dry tropical air masses are present. Since swamp coolers are much less effective during the monsoon season because they rely on evaporative cooling, it is feasible that this might contribute to increased minority mortality from heat later in the season.

New research will be presented to indicate that it is highly likely that the failure of evaporative coolers during the "monsoon" season is most likely responsible for the disparity between minority and white heat-related deaths, especially late in the summer. In addition, a means to employ a special "evaporative cooler advisory" into the already-existing Phoenix heat-health system will be suggested.