Roadways, Microclimates, and the Heat Island Effect

I’ve begun work on a hypothesis that’s an offshoot of my experiment last summer. It’s this; while cities are recognized as heat islands and are now being investigated for clues about how the biosphere will react to warmer climates and elevated levels of CO2 and other gases, I think we’ve also created such along our roadway net.
In essence, we’ve been modifying the planetary albedo, and thus the greenhouse effect, by paving streets and roadways. All of these surfaces are dark in color, black to dark gray, and are roughened to aid in traction. As such, they’re absorbers of solar radiation and are more efficient at this than sandy or grassy surfaces.
The ‘heat island’ effect is well known and documented. I’m not aware of any attempt to isolate this as to which percentage of the heat island effect is due to paved roads and alleys as opposed to, say, large buildings.
Meantime, while I was thinking about this, I came to the conclusion that roadways are the equivalent of cities in terms of modification of the planetary albedo. Indeed, cities are by their nature concentrations of roadways but there are equivalent amounts of modified surface sprawling across the continent.
I’ll be looking for evidence of this in the spring. There’s a master’s thesis in this for any student who needs a topic!
I plan to gather data of roadway temperature and the temperature of unmodified dirt a few meters away. The driving surface and any apron on the side of the road are all modified and all absorb heat. I’ll also look at vegetation patterns, if possible. Non-natural vegetation won’t help, and it’s common for highway departments to plant grass seed along the interstate highways. I’ll look for side roads that get the paving treatment but not the other modifications. I can then compare the grassed-over areas with natural areas to look for differences.
I have observed the numbers of forbs that flower in the late summer; they appear to be much more common a few meters away from the paved surface, often across fences that line the roads to prevent cattle from wandering into danger. Conceivably, the heat trapped by the roadways acts to extend the growing season and creates a microclimate that favors these. Goldenrod, a kind of blue daisy-like flower, certain yellow flowers, and pricklypoppies all appear to be more common near roadways than out in the middle of the natural desert area.
For those who don’t live in deserts, you might be interested in looking at your own roadway system. Even in green England and Europe, there might be discernable patterns of vegetation changes. You can write to me if you observe any such: I would be interested in hearing from you regarding your observations!


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