TitleUrban climate effects on extreme temperatures in Madison, Wisconsin, USA
Publication TypeJournal Article
Year of Publication2015
AuthorsSchatz, J, Kucharik, CJ
JournalEnvironmental Research Letters
Date Published2015
ISBN Number1748-9326

As climate change increases the frequency and intensity of extreme heat, cities and their urban heatisland (UHI) effects are growing, as are the urban populations encountering them. These mutuallyreinforcing trends present a growing risk for urban populations. However, we have limitedunderstanding of urban climates during extreme temperature episodes, when additional heat from theUHI may be most consequential. We observed a historically hot summer and historically cold winterusing an array of up to 150 temperature and relative humidity sensors in and around Madison,Wisconsin, an urban area of population 402 000 surrounded by lakes and a rural landscape ofagriculture, forests, wetlands, and grasslands. In the summer of 2012 (third hottest since 1869),Madison’s urban areas experienced up to twice as many hours ⩾32.2 °C (90 °F), mean July T MAX up to1.8 °C higher, and mean July T MIN up to 5.3 °C higher than rural areas. During a record settingheat wave, dense urban areas spent over four consecutive nights above the National Weather Servicenighttime heat stress threshold of 26.7 °C (80 °F), while rural areas fell below 26.7 °C nearlyevery night. In the winter of 2013–14 (coldest in 35 years), Madison’s most densely built urbanareas experienced up to 40% fewer hours ⩽−17.8 °C (0 °F), mean January T MAX up to 1 °C higher, andmean January T MIN up to 3 °C higher than rural areas. Spatially, the UHI tended to be most intensein areas with higher population densities. Temporally, both daytime and nighttime UHIs tended to beslightly more intense during more-extreme heat days compared to average summer days. These resultshelp us understand the climates for which cities must prepare in a warming, urbanizing world.