Might Xeriscaping Cause Heat Islands?

In my role as the book reviewer for the Connecticut Horticultural Society, I have been critical of certain books that rave about landscapes with hardscaping made of metal or rock (particularly if they don’t mention that these items are reclaimed or if they don’t mentioned how far they’ve been “trucked in.” There’s nothing sustainable about trucking tons of rock long distances).

But even after saying all of that, my primary concern, even in my own relatively cool and moist climate, is that these items collect and reflect heat and do not in any way sequester carbon from the atmosphere. Say what you want about the “monoculture” of the American lawn, at least it’s not reflecting blazing hot sun back at the house all day! It absorbs rainfall, and any polluting runoff from the driveway near the house (which a rain garden could do just as well–I’m no fan of the lawn, really). And so long as it is not irrigated (which ours is not) and is not mowed with a gas mower or trimmer (which ours is not) it has relatively low impact on the environment if one is not dumping synthetic fertilizers and pesticides on it to keep it green, and free of bugs and weeds (which I’m sure any long time reader of this blog can tell that we do not do–I shouldn’t even have to say that!)

So it was interesting to read this article on Accuweather about California and Nevada paying rebates to homeowners to reduce the square footage of their lawns.

What most interested me about the article was the second to last paragraph in which a meteorologist talks about how reducing lawn area significantly might lead to an urban heat island effect. This was the first time I’d seen anyone (other than me) worried about this sort of thing so it was nice to know that not only were my concerns valid, they were scientific as well.

Again, a lot of my photos here show an asphalt driveway, a brownstone wall, and a slate walk at my home, so I know a lot about the way hardscaping can cause “heat islands.” Further, since this is my sunniest spot, in summer, all of my containers are placed right on that asphalt driveway, up against, or on top of that brownstone wall so by mid-July they are literally baking. I’d say those containers were pretty much feeling very desert-like by 2 pm every afternoon.

What I also notice is that after I water them, that entire area cools down significantly–I’m guessing by at least 10 degrees although I’ve never measured it. It’s as if a cooling thunderstorm has passed through.

Were I growing all cacti and succulents there, with a reduced watering need, that area would cool off a lot less frequently (and consequently, probably, so would my house, even though it is shaded by large maples and oaks.)

Perhaps that’s why I’m so worried about all this stone and metal hardscaping as allegedly sustainable. Brownstone walls and slate walks in a climate like mine are great because the ice melts just a little bit faster off them in the winter.

But anything that is likely to cause temperature rise in the southwest–an already dry, arid and drought prone region–cannot be a good thing!

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4 thoughts on “Might Xeriscaping Cause Heat Islands?

  1. Such an interesting question you pose. I’ve often thought the same thing when I see recommendations for increasing hardscape. Many of the suggestions make me hot to look at them.

  2. I know exactly what you mean! And when I read that there were places in the desert southwest that were paying folks to rip up their lawns, it got me a little concerned. Now, I’m all for native plants and landscaping, and goodness knows, lawns are native to nowhere, really, unless you’re using prairie grasses in the Midwest, but I reviewed one book that showed landscaping with sheets of sheet metal. Ugh! How can that be sustainable? My plants get “sunburned” from light reflected off my bay windows. Can you imagine what happens to plants getting hit with heat and light from sheet metal?

    Thanks for your thoughts, as always!

    Karla

  3. Thanks for sharing your thoughts! I was surprised at how little information there is out there about the potential for xeriscaping to contribute to the urban heat island effect. I am trained as a landscape architect and about to make some landscaping decisions for my own home and started thinking about this. I ride my bike a lot, and you can really feel the difference in temperature between the city and the suburbs that is related to the degree of “hardened” surfaces. I’m hoping to avoid a lawn, but perhaps do something more along the lines of rain gardens (provided we aren’t flooding the basement!). Of course, we’ll be in Colorado, where you can’t even collect the rainwater that falls on your own property! http://www.nytimes.com/2015/06/16/us/a-thirsty-colorado-battles-over-the-destiny-of-its-raindrops-drought.html

    • Laura,
      Thanks for reading & for your thoughts. I posted about that NY Times article a week or so ago. I was shocked by it. I’ve spent a lot of time in Colorado –summers & winters –but that was one wrinkle I had never come across.

      I paired that with some thoughts about my profligate neighborhood, still running lawn sprinklers in the rain. One of my readers told me that in her area rain sensors are mandatory on new systems. We haven’t seen the wisdom of that here, even with drought in so many parts of the country.

      It is amazing how water cools though. I hope you find a solution you can live with. I suspect, with the right combination of plants, & perhaps a bit of supplemental drainage if necessary, your rain garden would be perfect.

      Karla

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