Climate change and health: A study of indoor heat exposure in vulnerable populations in Detroit, Michigan

A significant number of deaths are caused by heat in the United States, and public health researchers and scientists have realized that long term climate change could be important for future risk assessments as the average temperature of the globe increases. Heat related mortality and its prevention have not been adequately studied in southeast Michigan, specifically the city of Detroit. A recent literature review showed that risk factors for heat wave vulnerability include age, disability, poverty, housing, environmental factors (lack of green space around the housing complex or amount of impervious surfaces (i.e. concrete) and behavioral factors, such as not dressing lightly, and not using cooling devices). Additionally people spend approximately 90 percent of their time indoors. The young, the elderly, and the chronically ill, especially those suffering from respiratory or cardiovascular disease, that spend more time at home, could be at a higher risk of health affects from the inability to adapt or recognize the potential of heat related illnesses.

The primary research question of this study is to estimate indoor temperatures, during warm summer weather, based on building stock, ecological characteristics (how much land is covered by vegetation versus concrete, buildings or paving) and surface meteorological conditions in southeast Michigan. The main method of evaluation for this study is an exposure assessment of 30 different homes (1-level, 2-level and high rise residential buildings) in Detroit, Michigan to evaluate determinants of heat exposure during the summer months from June – September 2009 for elderly residents (over the age of 65 years). The assessment used direct measurements from environmental monitoring of selected dwellings. Continuous temperature monitors (HOBOS), were placed inside each home (as well as outside each home for a subset of homes) to automatically record temperatures in 30 minute intervals over the 3 month period. Modifiers of exposure related to the built environment, such as housing characteristics including date of construction, type of insulation, and number of floors for each dwelling will be examined in the model. Behavioral methods of adaptation to indoor heat exposure will also be captured in a daily activity log completed by study participants. This daily activity log has been completed by participants to record what actions (e.g., turning on a fan, opening windows, etc.) the residents have engaged in to get relief from the heat while indoors.

All results will be available by January, 2010. Preliminary results show indoor exposures that may threaten health. For example, on June 24, 2009, Detroit Metropolitan Airport (KDTW) recorded a temperature of 91 degrees Fahrenheit (check spelling) from 1:00 pm to 5:00 pm. Maximum indoor temperatures in one of the dwellings in a first floor room ranged from 75.9 – 79.4 degrees Fahrenheit, and continued to rise into the evening hours. As a comparison, a second floor room at another residence ranged from 88.7 – 93.2 during the same time period.

Variations in and determinants of indoor heat exposure in private residences are facets of environmental epidemiology that have not been well studied. A robust model that can provide better insight into parameters – meteorological, ecological and building characteristics – that can affect exposure is useful for assessing potential exposure measurement error and targeting public health interventions directly related to those elderly populations that are homebound, lonely and isolated, poor and/or old. The results of this ongoing exposure assessment study may inform building design strategies, improve our understanding of current exposure in residences, as well as provide data to refine our targeting of vulnerable populations for heat related illnesses and mortality. This study will provide information to help tailor adaptations for the public health and meteorological fields as climate change continues and the importance of preparedness and risk communication increases, especially in urban areas.