Low- and high-tech so­lu­tions for ur­ban heat peril

The China Post - - LIFE - BY RICHARD ING­HAM

Cli­ma­tol­o­gists call it the “ur­ban heat is­land” ef­fect — when a heat wave trans­forms a city into a fur­nace where cit­i­zens swel­ter, suf­fer or even die.

The phe­nom­e­non is a ma­jor worry in hot coun­tries where global warm­ing will drive peak tem­per­a­tures even higher in com­ing decades.

Ur­ban plan­ners and re­searchers, gath­er­ing in a par­al­lel con­fer­ence to U.N. cli­mate talks in Bonn, turned a spot­light on the prob­lem on Wed­nes­day.

But they also pointed to an emerg­ing ar­se­nal to fight it, from plant­ing trees to designing breeze-chan­nel­ing build­ings.

The ur­ban heat is­land de­rives from sim­ple physics.

Cities store heat from the sun and traf­fic in con­crete and tar­mac dur­ing the day, and re­lease it at night.

But in a heat wave, an in­fer­nal cy­cle starts up.

The night is not long enough for all the heat to dis­si­pate, so at dawn the new day is al­ready warm ... and can only get warmer.

With­out cool­ing or respite, old or sick peo­ple are es­pe­cially at risk. A heat wave that gripped Europe in 2003 killed more than 70,000 peo­ple, ac­cord­ing to peer-re­viewed re­search.

“Ur­ban heat is­land is a big prob­lem for us,” said Cata­rina Fre­itas, head of sus­tain­able en­vi­ron­ment man­age­ment for Al­mada, a city south of the Por­tugese cap­i­tal, Lis­bon.

The dif­fer­ence be­tween cen­tral Al­mada and its out­skirts can be a whop­ping 4 de­grees Cel­sius (7.2 de­grees Fahren­heit), she ex­plained.

“In the sum­mer of 2013, we were caught in a se­vere heat wave. We had 1,400 more deaths dur­ing this pe­riod com­pared to pre­vi­ous years ... We had a night­time tem­per­a­ture of 33 de­grees — we couldn’t cool down our bod­ies, it was a night­mare.”

Michael Boswell, a pro­fes­sor at Cal­i­for­nia Polytech­nic State Uni­ver­sity, said Los An­ge­les, a sprawl­ing car-de­pen­dent city of 4 mil­lion peo­ple and few parks, has also found it­self vul­ner­a­ble.

“Cur­rently, down­town LA ex­pe­ri­ences six days a year that ex­ceed 95 Fahren­heit or 35 Cel­sius,” he told AFP.

“By 2050 they an­tic­i­pate 22 days — and by 2100 they an­tic­i­pate 54 days.”

So what can we do to roll back ur­ban heat?

“The first thing that you can do is plant trees, to pro­vide shade,” said In­grid Con­inx at Wa­genin­gen Uni­ver­sity and Re­search Cen­tre in the Nether­lands.

“But when you plant trees you have to do it in the right way. If you pre­vent down­ward breeze from reach­ing the street, you could make things warmer and trap pol­lu­tion.

“So you have to have a bet­ter un­der­stand­ing of how your city in­ter­acts with the weather sys­tems and about the kind of veg­e­ta­tion that works best.”

An­other quick and rel­a­tively cheap weapon is mov­ing wa­ter: streams run­ning through cities are not only a source of plea­sure — they also ab­sorb a re­mark­able amount of heat from the air, said Con­inx.

Other ideas are “green” and “cool” roofs — plant­ing shrubs and trees on the tops of build­ings, or paint­ing or cov­er­ing roofs to re­flect sun­light.

“Green” roofs are popular in north Euro­pean cities like Ham­burg and Ber­lin, while Cal­i­for­nia brought “cool roof” re­quire­ments into its build­ing code in 2005.

But such mea­sures only ease heat with large-scale de­ploy­ment.

“If you do not go be­yond 20 or 30 per­cent of green roofs, you won’t see any re­sult at street level,” said Saskia Buch­holz of the Ger­man Me­te­o­ro­log­i­cal Of­fice.

Desert Test-bed

Mas­dar City, a brand-new city be­ing built in the United Arab Emi­rates and por­trayed as a cham­pion of ur­ban sus­tain­abil­ity, is be­ing closely watched for new ideas.

“They are seek­ing to re­duce heat ar­chi­tec­turally, through the shap­ing of build­ings and through wind tow­ers, which are big, clever tubes that cap­ture wind up above the roof line of the city and push it down to street level,” said Boswell.

Com­puter mod­els for map­ping city tem­per­a­tures us­ing satel­lites and in­stru­ments at ground level, are pro­gress­ing fast.

In the near fu­ture, such data could be in­cor­po­rated in real-es­tate apps, pre­dicted Con­inx.

“I can imag­ine that 10 or 15 years from now, home-buy­ers will con­sider whether a place will ex­pe­ri­ence a high num­ber of heat wave days — and this will trans­late into the price of the prop­erty as well.”

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