City of Phoenix to Plant Thousands of Trees to Combat Heat

Throughout the course of this summer, we’re going to focus on just that, the summer heat here in Phoenix, how we as natives live with it and some exciting news and facts that help define our wonderful city despite the difficult summers.  Today’s focus is on the City of Phoenix.  For those of us who live here, we know what the City of Phoenix means.  For outsiders, let’s be clear, the City of Phoenix is just one of many cities that make up Phoenix metro.  Phoenix is the largest by population and area, so it is widely known.  But other surrounding cities like Tempe, Mesa, Scottsdale and Glendale are also included in “Metro Phoenix”.

Recently, the City of Phoenix unveiled plans to increase the number of trees in the city.  This initiative has far-reaching consequences and is aimed at helping to not only cool the city but also to promote air quality and improve aesthetics.  This is a stirring proposition. Personally, I have lived in Phoenix metro for the better part of 30 years now and have genuinely felt a shift in temperatures.  Over the last decade in particular, we have seen a sharp rise in the number of days over 110 degrees.  Various factors are at play including a prolonged drought which has lasted 25 years, population growth and related, urban sprawl.  The urban sprawl may be the biggest culprit. 

As new subdivisions are built and the city expands outwards, more roads are paved, and more building are built.  Roads and buildings tend to absorb heat during the day while they dissipate it slowly at night.  It takes some time for the roads and buildings to get hot enough that they hold heat all night but suffice to say that by early to mid-June, they are high heat emitters when the sun is no longer shining.  This means that the city does not have the opportunity to cool off at night like it used to, the heat is still on until day breaks again.  The consequences are severe, not only do average day/night temperatures remain stubbornly high, but it also has an impact on the weather.  You see, the southwest is fortunate during the summer to receive moderate to heavy rainfall from monsoons.

Monsoons are a seasonal phenomenon whereby tropical moisture from the south is drawn into the hot desert regions by high pressure systems that change the usual westerly winds to ones from the south.  This can bring severe thunderstorms, flash floods, dust storms and much cooler temperatures.  When I lived here in the 90s, these were a regular occurrence.  Maybe 8-15 monsoon storms per summer.  In recent years we have been lucky to get 5 and in 2019/2020 we had almost none.  The lack of monsoons had been impactful.  Not only do they provide much needed moisture, but for days afterwards, they help tamp down average temperatures.

So what’s behind the change?  The prevailing theory is that Phoenix metro is now a heat dome.  Meaning that the heat is so intense that it forms a dome over the city that effectively wards off any kind of weather other than sunny and dry.  The heat dome is exacerbated by the streets and buildings holding and emitting the heat throughout the course of the night.  Monsoons often come in the late afternoon or very early morning hours.  Their frequency at both of those previously typical times is no longer.  This is where the trees may have a chance to make their biggest difference.

The City of Phoenix funded its first ever shade analysis finding that the median census tract has 11% tree canopy.  The goal is to have 30% tree canopy by 2030.  To accomplish this, an investment of $60 million dollars will be put towards 27,000 new trees and 550 new shade structures.  This change in shade may not be the end all be all solution, but it may, coupled with dramatic changes in how Phoenicians live, help slow down the continued march towards higher and higher daily temperatures during the summer.  Some of those other changes may include more stringent zoning for new homes plus an effort to build more sustainable multi-family living situations.  An emphasis on more drought tolerant grass and vegetation.  Increased public transportation to reduce the number of cars on the road.  Different types of pavements that are reflective of the sun and less prone to hold heat during the night.  Solar panels to create shade and lesson the demand for fossil fuel driven electricity.

The hope is that these sustainable efforts coupled with more shade will allow for our monsoon activity to ramp back up to more normal levels, thereby lessoning the number of ultra hot days and providing the drought-stricken region with much needed relief.  We are cognizant of the water situation too and have written about it in previous blogs: https://paradisevalleyestates.com/blogs/avenue-blog/avenue3-realty-water-article

For purposes of this article though, we want to focus on the notion that strategic shading may be one of the most effectual ways for the city to cope with its trend towards higher temperatures and lower annual rainfall.  We should have a good idea in less than a decade from now.  In the meantime, it will be interesting to watch the changes around the city as we start to see more trees planted!