Congratulations on your gardening skills, LA. Your efforts to landscape with drought-friendly plants, find alternatives to grass and generally be water-wise have contributed to our water district’s ability to beat water use reduction goals and be on our way to the 20 percent reduction that Governor Brown wanted us to hit by 2017.
Just one small problem: That water-sipping landscape might be making the city hotter.
Researchers have found that grass lawns and trees help provide shade from the sun and give off moisture to cool the air—which even the most realistic-looking artificial turf just can’t do. According to the USC study reported on by the LA Times this week, a Los Angeles with no lawns would be 3.4 degrees hotter at mid-day. Which isn’t great now, but since the city is also getting hotter each year due to climate change, those 3.4 degrees could really add up.
It’s not all dire, though. Gravel and low-water vegetation reflect more cool air in the dark of night than their greener counterparts. The nighttime cooling effect is in fact so strong—5.4 degrees—that it might cancel out the overall environmental warming resulting from the warmer daytime.
It remains, however, that most people are out and active during the daylight hours and a hotter, shade-free daytime is particularly problematic as the city tries to encourage more people to walk and bike rather than take cars everywhere. After all, the taking cars everywhere is kind of what got us into this in the first place, so it’s all a big circle.
One hypothetical solution offered in the study? Just get rid of everything. A city with not just no lawns, but also no trees or anything else, would actually be half a degree cooler than it is today. While that may seem counter-intuitive given the other findings, the reason is because trees in particular block breezes which would otherwise flow in straight off the ocean and across the city. (Just imagine, then, if we got rid of all the buildings, too!)