The typical California home's biggest area of water usage is beyond its four walls: its outdoor landscaping. So in the face of drought, tens of thousands of Los Angeles homeowners made a change last summer, reports the Times, swapping their grass for artificial turf, gravel, or drought-tolerant shrubs. And while water-conserving efforts have been indisputably successful—urban Californians cut their water consumption 21.5% in June as compared to June 2013,the Mercury News reports—a trio of landscaper designer wrote an op-ed in the Times last summer about an unwanted effect of "gravelscaping": hotter days due to fewer plants and trees "transpir[ing] moisture to cool the air." Now, researchers at the University of Southern California have run various land-cover scenarios to determine whether that's so.
In a nutshell, LA's daytime temps would be up to 3.4 degrees warmer thanks to the dramatic reduction in irrigation if the city went entirely without lawns. But, as they report this week in Geophysical Research Letters, if those lawns were replaced with drought-tolerant vegetation (as opposed to pavers and gravel), there would be a 5.4 degree dip in nighttime temps to more than make up for the daytime warming—a phenomenon they hadn't foreseen. "In retrospect, it makes sense that reducing soil moisture would change the thermal properties of the soil and surface-atmosphere coupling in this way," researcher George Ban-Weiss says. And if drought-tolerant shrubs were substituted for lawns and trees, daytime temps would dip 0.4 degrees thanks to unhindered sea breezes, not that the researchers are endorsing a tree-less LA.