Meltdown in Naptown 

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Efforts to respond to the varied and complex consequences of human-influenced climate change may be locked in long-term political quagmire. At the local level, though, the equation is simpler: It's a matter of life and death.

In Indiana's capital city, human activities such as deforestation and development — the very endeavors that created the city, really — fashioned a hot spot right in the center of the state. In effect, they've changed the climate. And, along with this increased temperature pressure, the city must cope with higher densities of vulnerable populations, most notably people without air conditioning.

Though tornadoes may be the top cause of weather-related deaths this year, extreme heat events are typically the no. 1 cause in North America, according to Daniel Johnson, an assistant professor of geography at IUPUI, the Center for Urban Health and Center for Health Geographics.

Each year, Indianapolis experiences an average of three deaths directly attributed to heat, but experts say this number is underreported because deaths attributed to cardiovascular or respiratory conditions may have been inflamed to fatal levels by high temperatures.

The pressures are at times much more marked, though, and widespread death occurs, Johnson told an audience gathered at the 2011 Indiana Environmental Health Summit earlier this summer. Examples he offered included an estimated 600 heat-related deaths in Chicago in the summer of 1995 and 181 deaths in Philadelphia in 1993. Also, heat, coupled with the effects of heat-related wild fires, was linked to 56,000 deaths in Russia last year, he said.

More deaths are noted in areas with higher surface temperature, he said.

In Indianapolis, Johnson works with emergency management and the Indianapolis Health Department to use mapping tools to locate areas of special concern. Researchers layer various types of information to develop strategies to combat heat-related emergencies.

click to enlarge Sattelite imagery of Indiana shows the marked surface temperature increase around urban areas.
  • Sattelite imagery of Indiana shows the marked surface temperature increase around urban areas.

"This is a good slide to show to anthropogenic climate change skeptics," Johnson said at the environmental summit, displaying a map of land surface temperature in Indiana that reflects dramatic differences between urban and rural surface temperatures as captured by NASA's MODIS, or Moderate Resolution Imaging Spectroradiometer, satellite. [See image.]

"Through changes we've made to our environment, we've changed the urban climate in these locations — this more or less can't be denied."

Local averages misleading

Average temperatures taken across the region may not reflect the magnified intensity experienced in what experts call urban heat islands. The regional forecast may, for instance, peg Indianapolis at 95, Shelbyville at 93, Terre Haute at 95 and Columbus at 92.

Likewise, intensity of summer heat does not average a certain number of degrees hotter with each new acre of asphalt sprawling beyond the urban core. Data compiled by the Indiana State Climate office underscore the ongoing variability of average temperature trends.

When the heat index hits 105 or higher, the National Weather Service typically issues heat advisories or warnings.

In the past two decades, the number of days crossing into this threshold of extreme heat range from a high of eight in 1990 to none in 2008. Last year, five days crossed over to that level. So far this year, at least two days have already hit that mark.

Indiana State Climatologist Dev Niyogi explained urban heat island effects are well documented and "highly localized" phenomena measured and experienced at a micro level.

By honing the MODIS data into a tighter scale, Johnson's mapping exercises reveal how these variations are expressed across different areas of the city.

The maps reveal what Johnson called "dramatic changes" in the distribution of urban heat islands in the past three decades and their relationship to vulnerable populations across the city between 1990 and 2000.

Johnson's team is waiting for the U.S. Census Bureau to release detailed elements of the recent decennial census, which will enable researchers to understand recent population shifts and better assess the city's current state of vulnerability.

Their definition of vulnerability includes socio-economic factors that influence a person's potential to access air conditioning in addition to features of the natural landscape such as percent of tree cover.

"We have seen the heat island become more dispersed which is not necessarily a good thing because with urban sprawl services are more thinly spread and the effects of mitigation strategies are diluted," Johnson told NUVO.

"Additionally, we have seen some changes in the social vulnerability and its spatial distribution. This, in coincidence with the dispersed urban health effects, can lead to different levels of vulnerability within Indianapolis."

Mapping vulnerability helps local health officials better implement heat-mitigation strategies, such as where they might introduce cooling centers and employ educational campaigns about the health hazards associated with extreme heat.

"High social risk areas usually have low tree cover," Johnson said.

Urban heat islands, which can run more than five degrees hotter than surrounding rural regions during the day, retain their heat when the sun goes down.

In the evening, the difference can run as high as 22 degrees, according to the U.S. Environmental Protection Agency.

Future Implications

Though urban heat islands are experienced on a micro-scale, with dramatic variations across a city's different neighborhoods, the implications of urban climate change present issues of much broader interest.

In addition to his position as state climatologist, Dev Niyogi is also an associate professor at Purdue University, specializing in land use, land cover change and its affect on weather and climate.

His recent research concerns the effects of urban landscapes on thunderstorm distribution. A study published by the Journal of Applied Meteorology and Climatology, in which Niyogi was lead author, found "that more than 60 percent of storms changed structure over the Indianapolis area as compared with only 25 percent over the rural regions."

This finding relates to earlier findings that "the distribution of urban area and anthropogenic heating could greatly influence the distribution and amount of regional rainfall" ultimately affecting the variability of precipitation around urban areas. Some studies have suggested that urban splitting of storm systems may reduce precipitation in large cities and increase storm intensity downwind.

Climate, Niyogi told NUVO, is like politics in that it is local and heavily influenced by the features in your backyard. Local environment influences everything from residents' general comfort to air quality, heating and cooling expenses and the severity of drought, he said.

Currently, Niyogi said, researchers are engaged in identifying risk assessment tools to help people devise the most effective decision-making tools in response to behavior of the local climate. Other topics of research exploring climate-change mitigation strategies include studies of urban tree cover, reforestation strategies and green roofing design.

Macro weather pressures such as thunderstorms are still natural and uncontrolled phenomena. Niyogi likens them to a hammer, while climate changes linked to human influence are more like a chisel: "While we can't control the hammer, the placement of the chisel is in our hands, at times, through local planning."

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