SHADY A PLAN

By 2030, Phoenix plans to have 25% tree cov­er­age in its ur­ban ar­eas

Yuma Sun - - DESERT LIFE - Desert Gar­dener Karen Bowen

Ipre­vi­ously wrote an ar­ti­cle about Sin­ga­pore, whose goal is to be­come a city within a gar­den. Now I am writ­ing about Phoenix, whose goal is to in­crease its shade from trees from 10 to 25 per­cent by 2030. The Tree and Shade Mas­ter Plan was adopted in 2010 and came about when Phoenix was study­ing a va­ri­ety of ways to de­crease sum­mer tem­per­a­tures within the city.

Ac­cord­ing to www. phoenix.gov, Phoenix has 92 days each year with tem­per­a­tures over 100 de­grees. The city en­com­passes 519 square miles and has over 1.5 mil­lion res­i­dents. Mari­copa

County is the fastest-grow­ing county in the United States, which is con­tribut­ing to the rapid ex­pan­sion of its ur­ban foot­print and in­creased ur­ban heat.

Stud­ies by Ari­zona State Uni­ver­sity showed that in­creas­ing Phoenix’s ur­ban tree cov­er­age from 10 to 25 per­cent could lead to a tem­per­a­ture re­duc­tion of 4.3 de­grees. If a neigh­bor­hood with no trees had a 25 per­cent tree canopy, its tem­per­a­tures could drop 7.9 de­grees. As sum­mer heat con­tin­ues to rise, adding more shade within Phoenix would help make the sum­mers more tol­er­a­ble, pro­vide res­i­dents with a more en­joy­able en­vi­ron­ment and be cost­ef­fec­tive.

In ASU’s Thrive mag­a­zine, fall 2018 is­sue, ASU pro­fes­sor Nancy Selover ex­plained that nat­u­ral ma­te­ri­als, such as trees, are less dense than con­crete and as­phalt and don’t con­duct heat very deeply. When night comes, heat stored by nat­u­ral ma­te­ri­als is near the sur­face and quickly dis­si­pates. Within a half-hour, a nat­u­ral sur­face will be cool, and you will have less heat stor­age.

The thought is that in­creas­ing the canopy cov­er­age from trees will in­crease the amount of nat­u­ral ma­te­ri­als avail­able to rapidly dis­si­pate heat at night, lead­ing to cooler day­time tem­per­a­tures. Twenty-five per­cent canopy cov­er­age will also in­crease cool­ing shade dur­ing the day­time.

Other cities that are re­al­iz­ing the ben­e­fits of in­creas­ing the num­ber of trees in ur­ban ar­eas in­clude Los An­ge­les, New York, Chicago, Hous­ton and Philadel­phia.

The con­cept of utiliz­ing trees to im­prove the en­vi­ron­ment is not new. In 1879, a Phoenix news­pa­per ar­ti­cle stated: “The tree plant­ing sea­son is now at hand, and we ex­pect to see it taken ad­van­tage of by al­most every­one in the val­ley. In this city let every per­son who owns a lot see that shade trees are set out. If noth­ing bet­ter can be ob­tained, set out cot­ton­woods. They cost noth­ing, (are) easy to plant, re­quire no care, and are of quick growth.”

There is al­ways the ques­tion of wa­ter when cities, es­pe­cially in Ari­zona and Cal­i­for­nia, talk about adding land­scap­ing. The con­tin­ued drought in the South­west has low­ered wa­ter lev­els in Lake Mead and Lake Pow­ell, our two main reser­voirs, and may lead to fu­ture wa­ter short­ages. So many states and tribes de­pend upon the Colorado River for wa­ter that in­creased use of wa­ter for land­scape pur­poses could be quite con­tro­ver­sial. In or­der for the Tree and Shade Mas­ter Plan to be suc­cess­ful, bet­ter wa­ter man­age­ment through im­proved plant­ing, ir­ri­ga­tion and main­te­nance prac­tices must be em­ployed to sig­nif­i­cantly lower wa­ter con­sump­tion.

An­other piece of Phoenix’s plan to re­duce heat within the city in­cluded the Phoenix Cool Roofs ini­tia­tive passed in 2012. The ini­tia­tive man­dated 70,000 square feet of ex­ist­ing city rooftops be coated with re­flec­tive ma­te­ri­als to help re­duce heat. Pri­vate and res­i­den­tial homes were not in­cluded in the ini­tia­tive. To date, this ini­tia­tive has not been ex­panded.

As cities in Ari­zona con­tinue to at­tract new busi­nesses and more hous­ing

is built to ac­com­mo­date in­creased ur­ban growth, hope­fully, mas­ter plans can be put in place that in­clude plant­ing shade trees and green ar­eas to off­set heat gen­er­ated by build­ings, side­walks and roads.

Cre­at­ing small oases of trees and other plant­ings in the midst of “con­crete jun­gles” will not only lower the heat in­dex but will also pro­vide a more calm and tran­quil en­vi­ron­ment for res­i­dents to live in. If wa­ter is avail­able, in­creas­ing the num­ber of trees within Phoenix, as well as within Yuma, is a win-win sit­u­a­tion for every­one.

Happy gar­den­ing.

PHOTO BY KAREN BOWEN

THE SWEET ACA­CIA IS A BEAU­TI­FUL TREE IN SPRING WHEN COV­ERED WITH HUN­DREDS OF ROUND, YEL­LOW BLOOMS. It is a drought-tol­er­ant tree that grows well in the desert South­west.

FILE PHOTO

A MAN SEEKS RE­LIEF FROM HEAT IN THE SHADE OF A TREE in the park sur­round­ing Her­itage Branch Li­brary in July.

PHOTO BY KAREN BOWEN

YUMA’S GAR­DEN CLUBS PLANT TREES IN PUB­LIC AR­EAS each year, in­clud­ing this mesquite tree planted by MGM Gar­den Club at Cross­roads Mis­sion. From left are El­iz­a­beth Moody, Barbara Rochester, Ja­nine Lane, Mary Lou Mil­stead and Ruth Ann Maguire.

LOANED PHOTO

MEM­BERS OF FORT YUMA RO­TARY HELP STU­DENTS at Gary Knox Ele­men­tary School plant a cit­rus tree in the school gar­den as part of a na­tion­wide cam­paign by Ro­tar­i­ans to in­crease the num­ber of trees in U.S. com­mu­ni­ties.

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