Photo: TreePeople

Los Angeles is a unique city with complex water and climate challenges. This makes our goal of growing a sustainable region no easy task. That’s why it’s so important to look at how water is used when we choose water wise landscapes or how our behavior will affect our city’s temperatures in the future.

Earlier this month, the Los Angeles Times published an article about how replacing lawns with drought-tolerant landscapes could potentially make LA hotter.

Thankfully, Professor George Ban-Weiss from the USC Viterbi School of Engineering released a study about how moving away from traditional lawns to drought-tolerant landscapes could have an effect on temperatures in LA. However, due to  many variables involved, this study focused on only a few basic possibilities.

Ban-Weiss looks at two different scenarios where irrigation was shut off completely to the yards.

The first scenario was to change all home lawns in LA to drought-friendly landscaping. The second scenario examined also changing all vegetated yards (traditional, high-water needs landscapes)  throughout LA to drought-tolerant designs. The control scenario was based off of average conditions in LA–  where trees cover around two-thirds of the city’s unpaved surfaces and the remainder of the spaces being covered in lawns and bare soil.

The study found overall that…

  • Night time cooling plays an important role– According to the two scenarios, nighttime temperatures would cool the city by 5.5 to 5.8 degrees, but would also have a daytime warming effect of 1.6 degrees. However, the study says higher levels of cooling at night will help people recover before facing the next day’s higher temperatures. The cooling benefits of transforming LA’s home yards definitely outweigh the small increase we might see in heat during the day!
  • The scenario matters– The study focused on transforming all lawns and/or all vegetation including trees! This would most likely never happen. It isn’t realistic for LA to cut down all of its trees and remove all its turf. So, the actual warming we would see would be less than the scenarios suggested. We need to see more research to learn what the temperature change would be if we kept our trees and only removed residents’ lawns. Trees cool our city!
  • The power of trees–  Planting a tree near a building cools the surrounding area thanks to its shade and evapotranspiration (when water is transferred from the ground to the air by evaporation and from plant transpiration). This would offset some of the warming reported from transforming a lawn into a sustainable landscape while also offering a number of other perks.
>Photo: TreePeople

Photo: TreePeople

Another important thing to keep in mind  is that irrigation causes a change in the thermodynamic properties of the soil. Put simply, that means when plants and soil are watered, additional heat gets trapped in the ground during the day, and the soil holds on to that heat for longer during nighttime (think of how quickly it gets cold at night in the desert!).

We are also working with leading experts to research the impacts of climate change and increasing heat on communities.

We can create a climate-resilient LA if we take action together, though! Let’s reach this goal by choosing beautiful, climate-appropriate landscapes and by planting and watering trees.

Want to learn more about what you can do to make a difference at your home? Join us for one of our free Green City Workshops where you can learn how to harvest the rain, install a native plant garden and other drought-smart tips!

This post was originally published on TreePeople’s Blog.

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