Watering Lawns Elevates Nighttime Temperatures!

a grass lawn replaced by creeping thyme will lower temperatures

A low-water thyme lawn charms with scent as well as beauty.

Lower Our Nighttime Temperatures!

Falling under the darned if you do and darned if you don’t philosophy, recent research shows that planting your yard with drought-tolerant species of plants leads to elevated daytime temperatures but lowers critical nighttime temperatures by more than expected.

A USC study out of California, where a long-term drought is ongoing, conducted by George Ban-Weiss along with Pouya Vahmani shows that xeriscaping – growing plants with low water requirements – leads to increasing daytime temperatures in the range of 1.3 degrees Fahrenheit. That’s because people would water their lawns less and therefore there would be less evaporative cooling. But conversely, nighttime temperatures may drop as much as six degrees Fahrenheit. Dryer soil reduces heat movement from the subsurface soil to the air.

Daytime vs. Nighttime Temperatures

While increasing daytime temperatures might seem like a bad thing in this age of global warming, research shows that it is elevated nighttime temperatures which lead to severe health issues and even death especially among the elderly and weak. Homeothermic animals – such as humans – need those cooler nights to allow their bodies to recover from high daytime heat. Our bodies work very hard when temperatures get too high to try to regulate our internal temperatures so that our chemical processes can work right. Those mechanisms need to rest at night to reset themselves to function the next day. It’s like a single line bucket brigade with no way to return the buckets for refilling without taking a break.

Water Vapor is a Greenhouse Gas

Not all greenhouse gases – i.e. those gases which help keep Earth’s atmosphere warm – are toxic. Water vapor causes the majority of global warming but carbon dioxide and many man-made gases contribute to our cloud blanket. Both CO2 and water vapor are harmless at the Earth’s surface but contribute to heat-retention in the upper atmosphere.

lower nighttime temperuatures by planting Ice plant shown in bloom

Ice Plant requires little water and blooms for a long time.

Replace High-Water Plants!

We would all be better off to replace plants with high water needs with those with lower water needs. This is especially true in turf-grass lawns which are now the number one cultivated plant in the US based on acreage (63 thousand square miles.) Allowing northern grass to sleep during low rain periods is better than watering it and keeping those nighttime temperatures high. Better yet is to replace your lawn with native plants that need little to no watering. The biggest change may need to be one of color fashion as green lawns give way to silver-blue or grey-green drought resistant plants.

Definitions:

  • Xeriscape – using plants with low-water requirements
  • Evaporative Cooling – as water (or any liquid) transitions from a liquid to a vapor it needs to absorb energy which it takes from the environment in the form of heat. We use evaporative cooling when we sweat.
  • Homeothermic – maintaining a steady body temperature despite external temperatures. Humans and most other mammals, most birds, and likely dinosaurs are all homeotherms while animals like snakes and insects – whose body temperatures vary with the environments temperature – are poikilotherms. Heterotherms such as bats and hummingbirds use both homeotherm and poikilotherm strategies.
  • Greenhouse gases are primarily water vapor, ozone, carbon dioxide, nitrous oxide and methane. These gases protect the planet from becoming a giant ice cube by holding heat within the atmosphere. However, like all good things, moderation is key. An over abundance of greenhouse gases causes global warming which threatens human survival. Much like a teeter-totter that is perfectly balanced, you can move one side or the other with a single finger. Mankind produces enough greenhouse gases to move the protective covering out of balance much like having too many blankets on a warm night.

Sources/Further Reading: Science Daily, Evaptainers, Colorado State University, Huffington Post

Image Sources: Dave’s Garden, Hobby Farms

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