Planning for cool
The researchers started in the city of brotherly love. “Philadelphia is already very active in climate change adaptation,” Sadoff said. After 1993, it became the first city in the country to begin a heat-health watch program. Social services ranged from opening cooling centers, handing out water bottles to the homeless, going door to door to check on people, and switching on the power to late electricity payers. But city adaptation measures take years.
Besides higher downtown temperatures and less nighttime cooling, the UHI extends its warmth beyond the city. Rainwater heats up on dark rooftops, rolls off hot pavement, enters storm drains, and pours several degrees hotter into nearby waterways, causing certain fish populations to plummet. So Philadelphia implemented greening efforts, ripping up unneeded pavements, planting rain gardens to collect stormwater and increasing green roofs, where living vegetation covers the tops of buildings to cool the city and mitigate runoff.
City officials were keen to know how their city adaptations were paying off. How could organizations effectively target their outreach programs? Could small changes on the block level affect a neighborhood’s temperature?
Those answers were exactly what Stephanie Weber, the lead scientist on the study, was hoping to find. The study set up an advisory committee consisting of about a dozen people from researchers, city officials, and utility representatives. She said, “We want to show people that data can be incorporated into simple policies for decision makers to use.”
But first, Weber needed to know how hot Philadelphia got. She took temperature data from ground-based thermometers, but since they are sparse, she added data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Aqua satellite, offered through NASA's Land Processes Distributed Active Archive Center (LP DAAC). Weber was able to get daily temperatures on a neighborhood scale, between 500 meters and 1 kilometer (0.3 to 0.6 mile) resolution, going back more than ten years.
“Now we had a quantity,” Sadoff said. Between 1980 and 2013, the number of heat wave days in urban Philadelphia increased from four to twelve days, while non-urban areas consistently experienced five days per year across the same time period. In addition, they found nighttime temperatures are not dropping like they used to, so people have less respite from heat. Sadoff said, “Having this information allows city officials and organizations to better understand the problem and to seek out funding to address it.” Still, which sections of town felt the heat the most? Who was at a higher risk?