The July 1936 Midwest Heat Wave: America's Second Worst Weather Fatality Episode. An Examination by use of the 20th Century Reanalysis Project

In the 1930's the United States experienced several brutal weather events; a prolonged drought, deadly heat waves, a frigid cold weather episode in the Northern Plains, multiple tornadoes and hurricanes, and floods. The focus of this study is on one year of that decade, 1936. The emphasis is on the heat wave in early to mid-July of that year. This heat wave was second only to the 1900 Galveston hurricane (e.g., 8000 deaths) in weather related mortality, as there were nearly 5000 heat-related fatalities. The goal of this study is to try and uncover the cause of the powerful heat wave and the high number of casualties. The investigation of weather events in the 1930's is hampered by the lack of upper-air data. Recently, the 20th Century Reanalysis Project (20C) was developed to provide additional weather variables including upper air data. This project, by the Physical Science Division (ESRL) from NOAA , is an effort to produce a reanalysis dataset spanning the 20th Century by the use of surface pressures, sea surface temperatures and sea ice distribution. The availability of this data enables one to look at the heat waves that plagued that decade. Heat is a silent killer and does not get much attention compared to other severe weather events. Heat was the leading weather-related cause of death in the 20th Century, with over 65,000 deaths. This mortality ensued the first half of the century prior to the availability of low cost air conditioning. . Prior to the 1930'sthere were there were several major (i.e., over 2000 deaths) heat waves in 1901, 1911 and 1917. In the Thirties three major thermal events took place: 1931, 1934 and 1936. All were very extreme but 1936 posted maximum temperatures as high as 49C (121F) in the Great Plains. Even with the 1980, 1988 and recent 2012 heat waves, some of these records still stand. The 1936 heat wave unfolded in two parts. Episode 1: July 5-16 in the upper Midwest and episode 2: from mid-July to late August in the Great Plains. Our interest is in the first event, the upper Midwestern region of Minnesota, Wisconsin, Michigan, Iowa, Illinois, Indiana, Ohio and Missouri. As shown in Table 1 these states account for about eighty percent of the 1936 heat fatalities. In addition, just across the border in Canada, 780 heat-related deaths were recorded in Manitoba and Ontario. Table 1 Heat deaths in Midwestern Episode State IA IL IN MI MN MO WI OH Total Deaths 400 634 304 608 750 644 336 283 3959 The killer heat started on July 6 and continued to July 16, with the worst days on the 13th to he- 15th . Heat deaths are concentrated in climates with long, cold winters (Koppen humid continental climate, Dfa and Dfb). This is the Kalkstein threshold concept: three of the seasons in this type of climate are cool or cold and a person is not acclimated to intense heat. Table 2 displays some examples of heat maxima during the first episode. A cold front moved into the region by the evening of 7/16 which eventually scoured out the hot air from the Midwest. This ended the first episode, but the heat reloaded into the southern the Midwest and the Great Plains to start the second heat event. This node of the heat wave was more intense but had fewer heat deaths as the geographical area contained fewer people and large urban areas. What caused the first early to mid- July node of the heat wave? The 20C project does provide some insight but mysteries remain, and there are certain aspects of the 20C output that are a bit puzzling so we are conservative about the interpretation of the results. 1. Midwestern heat waves are associated with upper level ridges, and this is what we see on the 500 millibar ensemble map for the Midwestern region in 1936. The geopotential, 500 millibar heights reach 5900 Decameters along the Canadian-Minnesota border. 2. On the surface we do not see a massive anticyclone rather a smaller cell. Prior to the July event there was a strong ridge and heat dome in the Southeastern states 3. The NWS daily Weather Maps series for July 1936 indicates a weak but steady flow from the Gulf of Mexico northward. 4. In terms of teleconnections the period 1935-1937 is in a neutral ENSO phase and there is a positive PDO 5. Feedback from the drought contributed to the heat intensity. Dry top soils absorb solar radiation and result in an additional infrared feedback of heat. In closing, one might ask: So What! With air conditioning we will not see a repeat of the high heat mortality of 1936. However, massive heat deaths were recorded in Paris (2003, 13,000 deaths) and in the Moscow region of Russia in 2010 (about 2000 deaths). Winston Churchill argued that “Those who fail to learn from history are doomed to repeat it.” With the advent of climate change if we have longer and more intense heat waves there might not be electrical power available to run AC units or there could be an economic affordability problem in paying for electrical power.