In a new study, research found that during heat waves, elderly people living in city areas where night temperatures remain higher are more likely to succumb to the heat than those in nearby suburban areas where temperatures dip when the sun goes down. The researchers discovered that night temperatures matter when they studied the 9-day hot spell that hit Paris, France, in 2003. The average temperature differences between the city and the suburb varied about 1 or 2 degrees during nights and days, respectively. Yet, even with these slight temperature changes, older people living in the city had twice the risk of dying from the heat than those in the suburbs, according to a study published in the journal Environmental Health Perspectives. The results suggest that certain areas of cities where heat concentrates called urban heat islands contributed to the disaster in Paris because they cooled down more slowly at night compared to the suburbs. These heat intensive areas are more common near city centres and tend to retain heat more than suburban areas due to the pavement and buildings made of heat-trapping cement and concrete. The findings increase understanding of how these urban heat islands impact human health. This is important as rising temperatures associated with climate change may increase the number and intensity of heat waves. Furthermore, the study tests the use of satellite images to more precisely identify the heat intensive areas that are more likely to affect people. Overall, more resources, improved communication with the public and better city planning could help reduce deaths due to prolonged summer heat waves, the authors suggest. Urban heat islands increase the intensity of prolonged hot temperatures heat waves for those who live in the heart of cities. Heat waves are associated with increased hospital admissions and death, especially in the elderly and children. These age groups are more vulnerable to the higher temperatures because their bodies cannot adjust to the heat as well as healthy adults. In general, heat waves mainly affect city dwellers, because more people live in cities where the heat concentrates. The temperature differences found between urban and suburban areas depend on time of a day, location, season and other factors. But, too few ground-based weather stations make it difficult to estimate the differences. Thus, how urban heat islands contribute to the health effects caused by heat waves is not well studied. During the current study, the researchers used more than 60 satellite images to identify and compare temperature differences between an urban area in Paris and in the suburban area Val-de-Marne during the heat wave in August of 2003. They estimated the daily mean, maximum and minimum surface temperatures and the day/night differences from the images. The estimates were a substitute for temperatures measured directly at city and suburban weather stations. The heat patterns were then compared to human health data collected from a previous study that included people 65 and older. They examined 241 persons who died in the studied regions during the heat wave and matched them with 241 persons of similar age, sex, city region and demographics who survived. They adjusted for age and other factors. Satellite images show that downtown Paris was a heat island with higher day and night temperatures than the suburban area. The difference in average high and low temperatures between the city and suburbs during the 9-day heat wave where study subjects lived was about 2 degrees and 1 degree Fahrenheit, respectively. Although higher temperature differences were seen in the day than at night, the researchers found that a major risk factor was night temperature, not day temperature. The researchers estimated that it doubled the risk of death in the older person living in Paris than a similar person living in the suburban area. These results highlight the importance for public health practitioners to target resources to elderly people living in hot spots. This study also suggests the need for urban planners to create more parks with grass and trees and implement other measures that will minimise urban heat islands and reduce heat-related health effects.
Environmental Health News, 13 April 2012 ;