How trees make cities health­ier

Financial Mirror (Cyprus) - - FRONT PAGE -

and safety threat is the air around them.

Al­ready, the World Health Or­gan­i­sa­tion es­ti­mates that 92% of the world’s pop­u­la­tion is ex­posed to dan­ger­ous air pol­lu­tion. Given rapid ur­ban­iza­tion – up to 70% of all peo­ple will live in cities by 2050 – the rate of ex­po­sure to higher lev­els of pol­lu­tion is ris­ing rapidly.

But ur­ban­i­sa­tion doesn’t have to cre­ate a health cri­sis. In fact, there is a beau­ti­fully sim­ple ac­tion that mu­nic­i­pal lead­ers can take to re­duce both ex­treme heat and air pol­lu­tion: plant more trees.

Trees and other veg­e­ta­tion nat­u­rally cool the air around them by shad­ing sur­faces and re­leas­ing wa­ter va­por. More­over, their leaves act as fil­ters, re­duc­ing PM lev­els in the sur­round­ing 30 me­tres by as much as one-quar­ter. It is a one-two punch of en­vi­ron­men­tal ac­tion.

My or­ga­ni­za­tion, The Na­ture Con­ser­vancy, has car­ried out a study of 245 cities around the world that stand to ben­e­fit from tree-plant­ing ini­tia­tives, es­ti­mat­ing their po­ten­tial re­turn on in­vest­ment in terms of both tem­per­a­ture and PM. Given that the most sig­nif­i­cant ef­fects of trees are highly lo­cal­ized, we found that densely pop­u­lated megac­i­ties in Pakistan, In­dia, and other parts of South and South­east Asia would ben­e­fit most.

The highly lo­cal­ized ef­fects of trees mean that plant­ing them can pro­vide highly tar­geted ben­e­fits, even in cities that os­ten­si­bly have plenty of green space. Con­sider Louisville, Ken­tucky.

With its lush parks and shaded neigh­bour­hoods, it would ap­pear to have lit­tle in com­mon with Mum­bai or Karachi. Yet there are neigh­bor­hoods in Louisville with min­i­mal tree cover, mak­ing the city one of the fastest-grow­ing heat is­lands in the United States – and prompt­ing The Na­ture Con­ser­vancy to ini­ti­ate a tar­geted tree-plant­ing ef­fort.

Count­less other neigh­bor­hoods world­wide could ben­e­fit from sim­i­lar ini­tia­tives. Ar­eas with vul­ner­a­ble pop­u­la­tions – near schools and hos­pi­tals, for ex­am­ple – are par­tic­u­larly good can­di­dates for such ef­forts. Trees can even be used as a nat­u­ral screen against pol­lu­tion from high­ways or in­dus­trial ar­eas.

World­wide, $100 mil­lion of an­nual in­vest­ment in tree-plant­ing ini­tia­tives could pro­vide as many as 68 mil­lion peo­ple with sig­nif­i­cant re­duc­tions in PM lev­els, while also pro­vid­ing 77 mil­lion peo­ple a re­duc­tion of 1C in air tem­per­a­ture. An in­vest­ment equiv­a­lent to $4 per per­son could save 11,000-36,000 lives an­nu­ally and re­duce ad­verse health ef­fects for tens of mil­lions of peo­ple.

That re­turn on in­vest­ment is com­pa­ra­ble to es­ti­mates for other strate­gies, such as in­dus­trial scrub­bers, lim­its on au­to­mo­bile traf­fic, and use of light-coloured building ma­te­ri­als that ab­sorb less heat. All of th­ese strate­gies have a part to play; trees alone won’t solve all of our heat and air-qual­ity is­sues. But only tree-plant­ing ad­dresses both ur­ban heat and air pol­lu­tion.

Trees also of­fer a host of other ben­e­fits for cities. They pro­vide habi­tat for wildlife, re­duce storm-wa­ter runoff, and se­quester car­bon from the at­mos­phere, which helps to mit­i­gate cli­mate change. There is also a grow­ing body of re­search show­ing that ex­po­sure to trees and other veg­e­ta­tion has a pos­i­tive ef­fect on men­tal health, es­pe­cially for chil­dren. All of th­ese coben­e­fits speak to the wis­dom of greater in­vest­ment in trees and ur­ban green in­fra­struc­ture such as parks and rain gar­dens.

The Sus­tain­able De­vel­op­ment Goals, which in­clude a ded­i­cated goal for sus­tain­able cities, have es­tab­lished ris­ing tem­per­a­tures and ur­ban air qual­ity as ur­gent global is­sues. Both will be dis­cussed ex­ten­sively at the an­nual United Na­tions Cli­mate Change Con­fer­ence, which starts next week in Mar­rakech, Morocco.

But th­ese are also lo­cal is­sues, ex­pe­ri­enced very dif­fer­ently in each city – and even in each neigh­bor­hood.

As global ac­tion on cli­mate change and sus­tain­abil­ity moves for­ward, mu­nic­i­pal lead­ers can take their own steps, start­ing with a tar­geted, lo­calised, and repli­ca­ble tree-plant­ing strat­egy that im­proves the health and well­be­ing of their res­i­dents. Time to get plant­ing.

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