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National Institute of Environmental Health Sciences

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New Microclimate Data Technology Points to Increased Urban Temperatures

By Wendy Anson

Using an innovative multi-site “micro-climate” data collection technology to capture temperature data in the Kibera slum in Kenya, a research team from Johns Hopkins University and Virginia Tech recently found their micro-climate readings regularly exceed those reported at the Kenya Meteorological Department Headquarters’ main observation station. Such temperature differences can delay needed heat advisories and other interventions when temperatures exceed a safe range.

The International Red Cross and Red Crescent Society, as part of an effort to protect people in low income countries from heat stress and other impacts of climate change, approached the Johns Hopkins team seeking assistance in characterizing heat exposures in the Nairobi informal settlements.

Anna Scott, the doctoral student in Earth and Planetary Sciences at Johns Hopkins who led the study, notes “A lot of people in tropical countries don’t think that heat stress is a problem, but it’s hard to say it’s not a problem if you don’t have any data to support it. Because there are generally no systematic ways to collect temperature data where the most vulnerable people are being exposed, we set out to collect temperature data at the neighborhood level that would be closer to a personal exposure than would a traditional centralized weather station.”

One third to 60% of Nairobi’s 3.1 million residents are estimated to live in these “informal settlements,” the largest of which is Kibera. Kibera’s residents are also vulnerable to heat exposure because they lack information on when heat waves occur and have poor access to routine health services, potable water, and cooling centers.

Urbanization itself can make city temperatures higher than nearby rural temperatures by several degrees. This “urban heat island effect” results from increased surface area from added buildings, increased heat retention from man-made materials, and decreased evapo-transpiration from a scarcity of plants and vegetative surfaces. The closely packed Kenyan slum homes are constructed largely of galvanized iron sheet roof-tops and concrete floors, with narrow entryways, and little ventilation.

Traditionally, weather measures in Kenya are taken by central monitoring stations. The Kenya Meteorological Department headquarters’ Dagoretti weather station lies approximately a kilometer from the residential areas of Kibera, however it is surrounded by a grassy, tree-lined campus unlike Kibera. The Dagoretti weather station records minimum and maximum 24-hour temperatures with analogue thermometers.

Multinational Team Investigates Local Climate

The team, which includes researchers and students from Kenya’s Intergovernmental Authority on Development (IGAD) Climate Prediction and Applications Centre, the University of Nairobi’s Department of Meteorology, and the Kenya Red Cross, studied Dagoretti’s daily minimum temperature from 1984 to 2014 to compute long-term climatological means for each day, and data from 2016 for temperature and relative humidity. They also used Landsat8 data from the same time period to assess vegetation and other surface characteristics that could influence local temperatures.

For their own measurements, the team installed a network of 50 iButton sensors, which were attached with zip-ties to the eaves of houses, posts and trees within Kibera and other neighborhoods, and which recorded climate data from December 2015 through February 2016. iButtons have been used effectively in other ecological studies and are accurate to .5 degrees Celsius.

Uniquely, to enhance air flow and ensure that heat from sunlight would not interfere with iButton heat measurement, the buttons were equipped with lightweight radiation shields designed by a team from the Maryland Institute College of Art and Johns Hopkins University.

Temperature data from monitoring stations
Temperature data from monitoring stations in the study show the differences between Dagoretti weather station readings and Kibera temperatures measured with iButtons.
(Photo courtesy of Scott, et al., 2017)

Targeted Interventions Can Provide Heat Relief

Julia Gohlke

Dr. Julia Gohlke’s studies on heat and health span the globe, from Alabama to Kenya.
(Photo courtesy of Virginia Tech)

Julia Gohlke, Ph.D., an associate professor of Environmental Health at the Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University and former NIEHS postdoctoral fellow, was a member of the Nairobi research team and also investigates extreme heat events in urban and rural Alabama. Scott collaborate with Gohlke on heat related research, often by installing thermometer networks similar to those used in the Nairobi study.

“There’s no doubt now that temperatures are increasing due to global change and we have robust literature showing adverse health outcomes linked with heat exposure,” said Gohlke. “But how much heat and the exact outcomes are less defined.”

Gohlke started out in toxicology using animal models to help establish base levels of temperature exposures and their effects, but changed her focus to climate and human health. “In fact, NIEHS is where I made the transition from doing primarily toxicology modeling with animals to looking at epidemiological study design. I always think of that time as one of the most fruitful and invigorating times in my research, with great collaborators and mentors like Chris Portier, who increased my understanding on the biostat[istics] side.”

The collaborators’ results show that air temperature in Nairobi does vary geographically, and that sensors located in informal settlements recorded consistently warmer than did the Dagoretti station. The team hopes that evidence of high urban heat events can trigger the implementation of targeted interventions in communities, such as providing heat wave warnings, and increasing the amount of vegetation and shade trees.

Citation: Scott AA, Misiani H, Okoth J, Jordan A,Gohlke J, Ouma G, et al. (2017) Temperature and heat in informal settlements in Nairobi. PLoS ONE12(11): e0187300.