How does the color (for example, white or black) or material of a rooftop affect the surface temperature of the roof? How do traditional roof surfaces compare to the surface temperature of a green (vegetated) roof?
It is well known (and shouldn't be a surprise!) that roofing materials can influence temperatures inside their structures. This is especially important in the summer, when air conditioning can be very expensive and the heat given off when an air conditioning system cools hot air makes a hot environment even hotter.
It is perhaps intuitively obvious that a white roof surface should be cooler than a black roof surface because a white surface will reflect more sunlight. It is also widely thought that green roofs should lead to cooler temperatures inside a structure both because of their reflective properties and because the heat released through the processes of evaporation from moisture in soil and transpiration from vegetation will cool the underlying surface. These effects can be quantified by measuring the surface reflectivity and surface temperature of various kinds of roofs. From a climate science perspective, this project is related to questions of land use and urban planning. How do changing patterns of land use modify climate — or do they? How can cities be designed to minimize urban heat island effects? Are we reaching a point where urban heat islands are no longer just "islands" — small local blips that have nothing to do with regional or global climate — but are becoming large enough to modify or even become the regional climate? Could there be advantages to being able to change surface reflectivity with the seasons?
This project requires two pyranometers (radiometers), an IR temperature sensor, and a data logger for each site. The radiometers must either be calibrated in units of watts per square meter per volt, or relatively to each other so that the output from the upward-pointing radiometer can be compared to the output from the downward-pointing radiometer. If you have access to an unheated/uncooled space below a roof, you could also measure air temperature below the roof. As in all good experiments, you need to isolate the independent variable (roof material) from other variables. This means finding roofs that are as similar as possible except for their roofing material. For example, all the roofs should be flat and not dramatically different in their exposure to sunlight. (Are they shadowed differently by trees or other buildings?)
These kinds of measurements have been made before. However, the thermopile temperature sensors and radiometers available through CSRES, which can be used with data loggers to monitor surface temperatures and reflectivities continuously, offer advantages that are not available with handheld instruments providing discrete measurements and requiring many trips to the study sites, almost certainly not including (as a practical matter) measurements during the night.
Brian Stone, Jr. The City and the Coming Climate: Climate Change in the Places We Live. Cambridge University Press, New York, 2012. ISBN 978-1-107-60258-8 (paperback) 978-1-01671-2 (hardback)