Considering that parts of the United State are in the grips of a heat wave, I created a graph (below) of U.S. heat-related deaths from 1986 to 2012. The outstanding years were 1995 primarily due to the over 700 deaths associated with the Chicago heat wave and the 1999 where another 100 deaths were associated with Chicago. In general, the graph shows that heat wave deaths have been higher since the mid 1990s than before. However, that pattern may be due to poor reporting of heat deaths before 1995.
Another interesting feature was that despite the high heat and prolonged drought last year (2012), the number of heat-related deaths was about the same as the two years before (2010 and 2011). One likely reason for that – at least for Illinois and the Midwest – was that while the air temperatures were high in 2012, humidity levels were lower due to the ongoing drought.
I am not an expert on heat wave deaths. However, I do know that deaths related to heat waves are hard to track down. Even coming up with the number for the 1995 Chicago heat wave was a challenge. In addition, heat may be a contributing factor in the death of someone already ill but not the real cause of death. So the true impact of heat is likely under-reported.
Results of the 1995 Chicago heat wave have shown that the elderly and low-income groups are most vulnerable. Also heat waves early in the summer are more deadly because people have not become acclimated to hot weather yet. Another important factor in heat-related deaths are the night-time temperatures. It’s hard to rest and recover from the day’s heat if it continues to stay exceptionally warm at night. Finally, many of the fatalities are not on the first day but increased in occurrence as the heat wave persists.