Heat Waves and Hot Environments

Hot weather is an important determinant of human mortality. In the United States, a major heat wave can cause literally thousands of excess deaths in a given summer. Yet, for purposes of public health, the term "heat wave" is not easily defined. "Hot" is a relative term, and periods of hot weather (heat waves) vary greatly in intensity and duration. Ambient temperatures may change rapidly, and they have marked diurnal fluctuations. Their effect on human beings is not the same in different geographic areas. Moreover, the microclimates, behaviors, and preexisting medical conditions of individual human beings dramatically affect the biological consequences of macroenvironmental heat. Thus, at the present time, a precise description of conditions constituting a heat wave of public health importance eludes description. Determining the precise hot weather conditions leading to an adverse impact on public health remains an important area for scientific investigation.