Increases in mortality during summer heat waves have been well documented in the United States, particularly in northern cities. Studies conducted in southern cities have shown weak or no relationships between oppressive weather and mortality during the summer. It has been previously assumed that people living in warmer climates are less sensitive to extreme heat due to physical acclimatization or indigenous urban structure. Recent studies suggest that heat-related mortality may in fact occur earlier in the season, especially in the South.
This research extends the original study period of June-July-August to include the spring months of April and May. Daily total mortality and daily heat index values are examined for several southern cities. Apparent temperature thresholds, above which mortality increases sharply, have been found for some cities, while other cities show no relationship.