UCCE Master Gardeners of San Bernardino County
University of California
UCCE Master Gardeners of San Bernardino County

Synthetic turf, dark mulch and asphalt surfaces are superheating our inland cities

I've been interested in surface temperatures of various living and non-living surfaces in our inland Southern California cities with increasingly hot urban heat islands for some time. Results are in! Use of dark asphalt, synthetic turf,

and dark colored mulches are superheating our cities.  The hottest material of the three is synthetic turf which topped at over 165 degrees in Palm Springs and 159 in Redlands on days when the ambient air temperatures were, respectively, 113 and 108 degrees F this summer. In five of ten days I took data during July in Palm Springs, I was barely able to take a photo before my trusted I-phone shut down, leaving me with the ominous screen heat warning shown here.

What can you do?

Take care of your trees, shrubs, groundcovers, and lawns, which cool the environment substantially.  In the same experiment, the coolest scenario was the surface temperature of a lawn growing in the shade of a mature tree.  Remember that, through transpiration, living plants cool the environment while non-living surfaces do not.

If you're tired of your high maintenance lawn, think about alternative groundcovers that have similar effects (see suggestions below).  While cool season lawns like tall fescue and ryes are high water-requiring plants, warm season lawns like Bermuda, zoysia, and buffalograss are more drought-resistant.  Our studies have found that it's not the lawns and groundcovers that waste the water, it's the uneven coverage (low distribution uniformity) of most sprinkler systems, coupled with not applying the right amount of water at the right time. This holds true for even the most drought-resistant native and non-native groundcovers irrigated via sprinklers, as well.  

Plant drought-tolerant groundcovers

There are dozens of groundcover species that are both drought and heat-tolerant suitable for California gardens.

Here are just two examples: 

Creeping thyme (Thymus serpyhllum) They are both drought resistant and do well in the heat. Fragrant flowers add a special touch to a meandering path to a secret backyard garden (below left). 

Rosemary (Rosmarinus prostratus) Some rosemary species are low-growing groundcovers.  It is great for rock gardens, growing to only 6 inches tall.  It produces purple flowers in the summer and attracts pollinators and can be used for culinary purpose (below right). 

trees cool urban heat islands
trees cool urban heat islands

Posted on Friday, July 30, 2021 at 12:01 PM
Focus Area Tags: Family, Health, Natural Resources, Yard & Garden

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