著：（美）喬納森·巴奈特 譯：徐搏謙

針對氣候變化危害的預(yù)測，具體取決于各國溫室氣體減排的進展。然而，在過去50年中，全球已經(jīng)排放了大量的溫室氣體，所有針對21世紀(jì)中期的預(yù)測都大同小異。溫室氣體排放逐年增加，增速也并未放緩。目前大氣中的溫室氣體含量已經(jīng)足以引發(fā)氣候危機，至2050年，氣候危機將更為嚴(yán)峻。問題惡化的態(tài)勢甚至比科學(xué)家?guī)啄昵暗念A(yù)測更為迅猛：河濱洪泛頻發(fā)、極端暴雨屢現(xiàn)、山火危機四起、熱浪持續(xù)不斷、糧食、飲用水緊缺。

因為未來設(shè)計城市所面臨的環(huán)境條件將與如今大不相同，城市設(shè)計實踐正經(jīng)歷著重大變革，將一直持續(xù)至21世紀(jì)中期。

世界各地的現(xiàn)代城市設(shè)計都建立于2個前提之上：一方面，自然環(huán)境在數(shù)十年，甚至數(shù)百年的時間內(nèi)維持不變；另一方面，工程行業(yè)能夠根據(jù)城市和其基礎(chǔ)設(shè)施概念改造物質(zhì)空間。

在沿海岸線及河流的開發(fā)建設(shè)，在幾年前可能毫無爭議，如今看起來卻不夠安全。橋、水壩、防洪墻、地下基礎(chǔ)設(shè)施等，即使在建設(shè)時期滿足所有工程指標(biāo)，如今也可能面臨危機。

在現(xiàn)在設(shè)計理念的指導(dǎo)下的人工場地，包括動用大量土方整理的、通過填埋洼地創(chuàng)造的、以管道圈圍河流的、大面積建筑和硬質(zhì)鋪地覆蓋的、優(yōu)質(zhì)農(nóng)田轉(zhuǎn)化為城市建設(shè)用地的等，將來則可能不可持續(xù)，甚至需要被修復(fù)。

我們也要重新思考那些需要大規(guī)模制冷制熱的玻璃幕墻樓宇、疏于考慮空氣流動的建筑排布，以及高度依賴汽車的交通方式。

無論是現(xiàn)在還是將來，保護人類免于氣候變化危害的措施因地而異。未來的風(fēng)險必須通過最準(zhǔn)確的科學(xué)信息來判定，而如何針對城市進行韌性設(shè)計并應(yīng)對這些風(fēng)險，將會成為城市設(shè)計師、規(guī)劃師、建筑師、風(fēng)景園林師和工程師的核心任務(wù)。

海平面上升會為沿海地區(qū)帶來前所未有的且持續(xù)反復(fù)的洪澇災(zāi)害。暴風(fēng)雨天氣中的潮汐起伏會更具破壞力，并波及更遙遠的內(nèi)陸地區(qū)。河道內(nèi)匯集的降雨持續(xù)增長，雨水可能會越過甚至沖走防洪墻。強降雨將超過地方雨洪管理能力的荷載。擬定保護措施并轉(zhuǎn)移居民遠離危險區(qū)域?qū)蔀槭滓蝿?wù)。

也需要為部分山火日益頻發(fā)的地區(qū)擬定保護措施，或?qū)⒕用褶D(zhuǎn)移至安全區(qū)域。城市需要增設(shè)戶外納涼設(shè)施、提升空氣流動性、鼓勵建設(shè)耐熱建筑，應(yīng)對持續(xù)的炎熱天氣對城市健康的危害。干旱和極端炎熱時，供水受到威脅，導(dǎo)致農(nóng)作物歉收。保障食物安全也將成為設(shè)計的優(yōu)先任務(wù)。

2017年通過的《中國城市設(shè)計管理辦法》提供了一個范例：一個全國性的氣候變暖管理辦法，涵蓋廣泛的城市和風(fēng)景園林設(shè)計問題，以及針對氣候變化的規(guī)劃、建筑、工程要求。

1 洪泛如何影響城市設(shè)計

土地與水的關(guān)系正處于變化之中，要求我們在開發(fā)新空間、重塑舊空間時，采取新的城市設(shè)計方法。

1）重新設(shè)計濱水走廊。在城市設(shè)計領(lǐng)域，將濱水沿岸廢棄工業(yè)用地改造為公共空間，是提升城市的最重要方式之一。公園、步道，以及餐飲等濱水節(jié)點早已普及并大受歡迎。然而，氣候變暖無疑將改變這些濱水走廊的設(shè)計以及人們的使用方式。目前，在部分海濱城市的濱水走廊周邊，海平面上升已經(jīng)導(dǎo)致潮汐變化加劇、風(fēng)暴潮危機惡化。濱水公園也將面臨海平面上升，以及極端暴雨時更加嚴(yán)峻的洪泛危機。到21世紀(jì)中期，所有的公共濱水空間都需要針對海平面上升重新設(shè)計，以保護周邊城市建設(shè)區(qū)域免遭洪澇災(zāi)害。濱水走廊需要加高、加固。而沒有濱水走廊但毗鄰水體的場所，則需要采取應(yīng)對洪泛及巨浪的保護手段，常用方式包括建設(shè)集公共設(shè)施和防洪墻于一體的多功能濱水走廊。對城市設(shè)計師而言，新的挑戰(zhàn)將是如何在保持可達性和建造公共設(shè)施的基礎(chǔ)上，有效地加入洪泛保護措施。

大部分城市濱水走廊的設(shè)計都盡可能地拉近人與水的距離，比如船只經(jīng)常緊沿岸線停泊。然而，為保護城市免受氣候變化影響，意味著需要通過建設(shè)防波堤、引入紅樹林或其他保護性濕地來增大人與水的距離。使濱水走廊遠離河流、擴展洪泛平原面積則是一種新的雨洪管理方法，其中部分也意味著將原有的城市建成區(qū)海綿化，以在洪泛危機時安全地緩存降雨。在洪泛周期性頻發(fā)的地區(qū)，可以將濱水空間設(shè)計為高、低2種空間。低空間可以允許其被洪水淹沒，恢復(fù)常態(tài)后通過快速清理再重新向公眾開放；高空間則需要保持高于洪水水位線以保護城市邊界（圖1）。

1 漢堡市漢堡港城的馬可波羅臺地，由巴塞羅那Miralles Tagliabue EMBT事務(wù)所設(shè)計，用以允許Elbe河在洪泛期可淹沒下層低空間。水位下降后，廣場可被快速清理，一年中的大部分時間人們都可以走近水岸。上層與街道有相同標(biāo)高的公共空間則不受洪泛影響。允許汛期河水淹沒的設(shè)計，將成為濱水空間開發(fā)必不可少的一部分The Marco Polo Terrassen, Hafen City Hamburg is designed by the Barcelona Firm, Miralles Tagliabue EMBT so that the Elbe river can flood the lower levels as shown in this photo. When the water goes down, the terraces are easily cleaned,and people can access the edge of the waterfront for most of the year. The portions of the public space up at street level are safe from flooding. As river flooding increases, designing to accommodate it will be a necessary part of waterfront development

2）重新設(shè)計公共空間以進行水管理。全球氣候變暖將會帶來更多的極端暴雨，而強降雨引發(fā)的洪泛很可能對城市的排水系統(tǒng)造成負(fù)擔(dān)。城市公共開放空間可以被重新設(shè)計為雨洪管理系統(tǒng)，海綿城市政策中的綠色基礎(chǔ)設(shè)施（圖2）。然而現(xiàn)有的公共開放空間選址和設(shè)計，通常缺少對自然地形和排水的重視，因此重新設(shè)計時需要優(yōu)先考慮雨洪管理。建筑群內(nèi)的私有開放空間也應(yīng)重新設(shè)計并納入雨洪管理系統(tǒng)。另外，還需要評估現(xiàn)有的排水基礎(chǔ)設(shè)施，尤其是標(biāo)高較低、排水口可能會因水位上漲而阻塞的管道。

3）強化基礎(chǔ)設(shè)施抵御洪水的能力。除雨洪系統(tǒng)外，也要評估地下交通系統(tǒng)、沿海鐵路和公路、排污管道的尺寸位置，以及現(xiàn)有堤壩防洪墻的穩(wěn)定性和有效性。部分基礎(chǔ)設(shè)施可能需要調(diào)整或重建以滿足新的設(shè)計標(biāo)準(zhǔn)。這將是一個大工程，應(yīng)立即開展研究。

4）強化建筑抵御洪水的能力。需要修正建筑相關(guān)的政府規(guī)范以保障結(jié)構(gòu)安全，尤其在缺少防洪墻保護的地區(qū)，保證建筑能夠承受洪泛沖擊。供暖通風(fēng)器械、電梯升降系統(tǒng)和其他裝備設(shè)施需置于建筑屋頂或高層。建筑的居住層必須遠高于洪泛平原，可采取的措施包括填方提升街道、土地、建筑的最低點標(biāo)高，或通過底層架空抬高建筑。有洪泛風(fēng)險的城市建成區(qū)需要更新甚至重建。建筑規(guī)范的調(diào)整意味著建筑師、風(fēng)景園林師和城市設(shè)計師必須重新構(gòu)思城區(qū)或鄉(xiāng)村設(shè)計以保障居民的安全。

5）逐漸搬離無法保護的地區(qū)。在一些特殊地區(qū)，對建筑和基礎(chǔ)設(shè)施進行防洪保護可能不切實際或過于昂貴，抬升構(gòu)筑物、持續(xù)提供基礎(chǔ)設(shè)施支持也將徒勞無功。需要確定這些地區(qū)的位置，分階段地轉(zhuǎn)移居民，盡最大可能減少對其生活造成的干擾。如果某一天這些地區(qū)完全無法居住，應(yīng)確保所有人已經(jīng)安全轉(zhuǎn)移，將土地退還給大自然。

2 山火如何影響社區(qū)設(shè)計

山火是一種反復(fù)發(fā)生的自然過程。當(dāng)人類和其所擁有的不動產(chǎn)擋住山火蔓延的路線時，山火便成為一個難題。與洪泛危機的日益惡化不同的是，林地和草地中的山火終將熄滅。在山火發(fā)生后，自然資源會再生（這一過程對新環(huán)境來說更加合理），再次引發(fā)山火的概率至少在很多年內(nèi)會大大降低。但是這種大規(guī)模將花費極長的時間，21世紀(jì)中期前，山火危機很有可能將一直持續(xù)。

1）設(shè)計分隔開發(fā)區(qū)和荒野地。保護人和建筑免遭山火危機的最好方式就是分隔。批準(zhǔn)林地中的建筑項目建設(shè)一直存在著風(fēng)險。但是，過去人們知曉酷暑和干旱的周期，認(rèn)為自己了解山火危機，常用商業(yè)保險保證財產(chǎn)安全。然而，隨著酷暑季節(jié)延長，昆蟲侵害森林的時間、樹木草地因干熱失水的時間也都相應(yīng)增加。植物難以適應(yīng)新環(huán)境并逐漸凋亡。凋零的植被和干旱的荒原一旦遇到閃電或來自人類的一點星火，一觸即燃。

雖然風(fēng)能帶動火跨越開放空間，但也僅限于在有限的距離內(nèi)傳播。在易燃的荒野地中，如果構(gòu)筑物和小村莊周邊有足夠?qū)挸ǖ目臻g，它們也可能免遭山火之災(zāi)。因此，在森林與開發(fā)區(qū)之間，設(shè)計足夠?qū)挸ǖ目臻g，即防火區(qū)，能保護荒野地邊界的開發(fā)區(qū)。存在山火風(fēng)險的地區(qū)需要根據(jù)分隔原則重新設(shè)計。

一個更復(fù)雜的設(shè)計問題則是，如何找到未來存在山火風(fēng)險的地區(qū)，并重新設(shè)計這些場地以保證人們的安全。長期以來，歷史性的公園和林地已經(jīng)成為城鎮(zhèn)的一部分，需要進一步研究來決定如何調(diào)整。

2）強化建筑和地區(qū)抵御山火的能力。存在山火風(fēng)險的地區(qū)，建筑規(guī)范應(yīng)要求屋頂與墻體使用可防火的建筑材料。門窗和通風(fēng)口也有必要按照阻隔灰燼和火焰的標(biāo)準(zhǔn)來設(shè)計。建筑延伸向外的陽臺、門廊，及其他構(gòu)筑物也使用防火材料，或與主結(jié)構(gòu)保持足夠的距離（圖3）。

3 照片來自澳大利亞新南威爾士政府，展示了山火后的2處住宅。圖中左下的住宅被樹林緊密圍合，山火輕易地蔓延并燒毀了建筑。圖中右上的住宅則因周邊空曠而未受影響。在有山火風(fēng)險的地區(qū)，分隔建筑和荒野地、分隔社區(qū)和荒野地是基本的設(shè)計原則This photo from the government of New South Wales in Australia shows two houses after a wildfire, called a bushfire in Australia. The house at lower left was surrounded by trees, and the fire easily jumped to the building and destroyed it. The house at upper right survived because it is in a more open setting. Separation of individual buildings from wildland, and separating communities from the edges of wildland, are basic principles for designing in places where wildfire is likely

3）逐漸搬離無法保護的地區(qū)。如洪澇災(zāi)害嚴(yán)峻的地區(qū)一樣，對某些特殊地區(qū)進行防火保護也可能不切實際或過于昂貴。需要分階段地轉(zhuǎn)移居民，盡最大可能減少對其生活造成的干擾。因為山火危機也許會迅速發(fā)展，可能需要盡快行動。某一天如果這些地區(qū)完全無法居住，應(yīng)確保所有人已經(jīng)安全轉(zhuǎn)移，將土地退還給大自然。

3 熱浪如何改變城市和建筑設(shè)計

在許多鮮有炎熱天氣的城市中，連續(xù)數(shù)周甚至數(shù)月不間斷的極端酷暑天氣正成為一種常態(tài)。通過人工制冷系統(tǒng)調(diào)節(jié)建筑室內(nèi)溫度，不僅會增加能耗，也會將熱能轉(zhuǎn)移至建筑周邊區(qū)域，導(dǎo)致室外環(huán)境更加惡劣。建筑師和城市設(shè)計師需要重新利用過去沒有空調(diào)時的自然制冷技術(shù)，并在夏季氣溫過高、長期極端炎熱的地區(qū)，將其融合至城市設(shè)計和建筑規(guī)范之中。

1）設(shè)計街道、開放空間和建筑以促進自然空氣流通。合理的街道及開放空間規(guī)劃，在白天能夠利用盛行風(fēng)向促進空氣流通，更重要的是，在夜晚冷空氣可以在城市中流動并驅(qū)散積累的熱量。建筑設(shè)計也可以結(jié)合自然氣流，利用通風(fēng)塔使城市上空的冷空氣流入建筑，或者在夜晚將冷空氣引入建筑底層，推動熱空氣向上攀升，再從建筑的通風(fēng)塔中排出。

新的MDF/HDF工廠在北安恰爾邦Sitarganj的安裝工作在去年年中開始，在2月28日生產(chǎn)出第一張板材。

2）為街道和建筑遮陰。在密集的城市建設(shè)區(qū)，大面積種植行道樹能夠降低環(huán)境溫度，不僅服務(wù)于樹蔭下的行人，也影響著周邊區(qū)域。在遮陰樹難以存活的炎熱干旱地區(qū)，可以建造遮陰篷，可考慮用金屬結(jié)構(gòu)和遮陽織物材料組合（圖4）。

4 北澳大利亞達爾文市跨主商業(yè)街建造了這一實驗性的遮陰結(jié)構(gòu)，為行人和汽車降溫，這一地區(qū)的氣候不宜遮陰樹成長。設(shè)計本意是讓中間種植池內(nèi)的藤本植物生長攀爬并覆蓋構(gòu)筑物。盡管從照片拍攝至今植物有一定的生長，但藤本植物仍未生長至完全覆蓋構(gòu)筑物，稍顯遺憾。如果這一遮陰結(jié)構(gòu)成型，這條街的其他街區(qū)也同樣可以復(fù)制。如果可以營造一條連續(xù)的遮陰廊道，當(dāng)?shù)氐奈夂驅(qū)⒆兊酶鍥?。也可選擇在類似的結(jié)構(gòu)上覆蓋織物The city of Darwin, in northern Australia, has built this experimental shade structure across a principal retail street to cool pedestrians, parked cars, and traffic in a climate where shade trees will not grow to be big enough to make a meaningful improvement. The shade is to come from vines which are intended to grow from planters in the middle of the street and spread over the structure. There has been some disappointment that the vines have not yet grown across the whole structure, although there has been progress since this photo was taken. If the shade shelter does become successful,others like it can be built on additional blocks of the street. If an entire shade corridor can be created, it will have a substantial cooling effect for the local microclimate. An alternative method would be to cover a frame similar to this one with fabric

玻璃幕墻建筑本質(zhì)上是一種加熱室內(nèi)空間的機制。吸收的熱能可以通過空調(diào)來平衡，但會產(chǎn)生更大的能耗，并將熱能轉(zhuǎn)移至周邊城區(qū)。先進的玻璃技術(shù)可以減少熱能吸收，但外懸遮陰結(jié)構(gòu)也是一種選擇。這種設(shè)計理念在20世紀(jì)中期頗為流行，但是人們長期以來更喜歡光滑、反光的高層建筑。目前正是設(shè)計師和規(guī)范制定者們優(yōu)先考慮減少建筑熱量吸收的時機，特別是在極端炎熱問題日益嚴(yán)峻的情況下。

4 淡水短缺時的土地和建筑設(shè)計

一些地區(qū)的降雨減少也是氣候變化產(chǎn)生的影響之一，到21世紀(jì)中期將會更為嚴(yán)重。

1）治理沙塵暴。沙塵暴是干旱的后果之一，可用種草固土等防沙、治沙措施治理沙塵暴。種植覆土作物并限制播種時的翻土量，能夠受減輕耕地風(fēng)化侵蝕程度。類似的措施亟須在干旱地區(qū)大規(guī)模采用，也需要在21世紀(jì)中期前繼續(xù)推廣。

2）區(qū)域生態(tài)修復(fù)。中國引領(lǐng)著對大尺度區(qū)域生態(tài)修復(fù)的探索，包括森林保護、防風(fēng)固沙、草原保育。于1994年開展的“黃土高原水土保持”項目，采取限區(qū)域批準(zhǔn)農(nóng)耕、放牧和伐木活動的措施，并大規(guī)模植樹造林，取得的成功已引起了國際上的關(guān)注。目前，已有相當(dāng)一部分地區(qū)從過去的干旱、類沙漠土地變?yōu)槿缃竦木G地（圖5）。這種大尺度的生態(tài)修復(fù)也會增加降水量，并進一步提升植被覆蓋率。

5 中國修復(fù)了黃土高原5%的土地，吸引了全球關(guān)注，其中包括埃及西奈半島也嘗試了類似的修復(fù)。2張照片展示了20世紀(jì)90年代中期和近幾年的地貌景象。這種轉(zhuǎn)變的產(chǎn)生需要與當(dāng)?shù)剞r(nóng)民緊密合作，改變他們過去的種植、伐木、放牧經(jīng)驗，再從非常細(xì)微的尺度重新設(shè)計、重新種植。這種生態(tài)再生方法可以增加當(dāng)?shù)亟涤炅?、提升農(nóng)田產(chǎn)量、改善區(qū)域環(huán)境The regeneration of about five percent of the land in China’s Loess Plateau has attracted international attention, including plans to attempt a comparable re-greening of Egypt’s Sinai Peninsula. The two photos show the condition of the landscape in the mid-1990s and a few years ago. The transformation required working closely with local farmers to change planting, tree-cutting, and grazing practices and then a redesign and replanting of the landscape at a very detailed level.This kind of landscape regeneration can increase local rainfall, making farms more productive and improving the climate for the whole area

3）減少工業(yè)冷卻用水。發(fā)電廠和其他工廠經(jīng)常利用溪流中的淡水制冷，再將可能已受到污染的水資源以更高的溫度排放回溪流。關(guān)閉制冷系統(tǒng)，利用同樣的水源反復(fù)在場地內(nèi)流動，通過自然蒸發(fā)而散熱是一種雖然成本更高但卻更簡單的替代方案。這種方案需要大面積的制冷池，因此這些工業(yè)設(shè)施也需要更大的場地。

4）節(jié)約灌溉用水。農(nóng)業(yè)生產(chǎn)需要大量的淡水。大量澆灌農(nóng)田雖然非常簡單，也是種植水稻的必要方法，但是大量澆灌其他作物卻意味著會因蒸發(fā)浪費大量的水資源。噴灌，即通過噴頭制造人工降水以大面積覆蓋農(nóng)田，也會因蒸發(fā)或無效灌溉而浪費大量水資源。最節(jié)水的方法是通過地下多孔管道灌溉。管道系統(tǒng)的設(shè)計決定著農(nóng)田的布局，需要考慮不同的管道容量和農(nóng)田間距，

5）管理飲用水供給。許多城市因管道泄露而浪費了大量的水資源。如果泄漏率超過10%，水源緊缺的地區(qū)就需要制定維修更換計劃。相似地，許多家用電器和民用、商用制冷系統(tǒng)，也正大量消耗著不必要的水資源。長年累月，更換后的節(jié)水設(shè)備會顯著減低總耗水量。采集雨水進行園林灌溉，維護建筑周邊植被，可以節(jié)省稀缺的飲用水資源，因此，居住區(qū)和商業(yè)區(qū)的園林設(shè)計需要利用這種方式收集雨水，并儲存于容器中，再抽取用于日常園林灌溉。在水資源需求快速增長并超過供給的地區(qū)，這些管理方式顯得尤為必要。

5 應(yīng)對未來糧食短缺

到21世紀(jì)中期，人口的日益增加，以及種植周期的逐漸變化可能共同導(dǎo)致部分國家糧食短缺，甚至目前糧食供給穩(wěn)定的國家也不例外。隨著種植周期的變化，農(nóng)作物將不再適應(yīng)其已經(jīng)生長了數(shù)個世紀(jì)的環(huán)境。而其他地區(qū)的氣候卻可能會變得更適宜這些作物生長，但土壤條件卻很可能有所差異，況且也無法確定農(nóng)作物可以根據(jù)氣候環(huán)境變化而遷移。糧食生產(chǎn)國會因自身糧食短缺而減少出口，所以依賴進口糧食也并不可靠。

2）充分利用溫室農(nóng)業(yè)。用透明塑料或玻璃結(jié)構(gòu)保護農(nóng)作物，可以延長植物的生長周期，在遮陰設(shè)備的保護下也可以保護作物免受過冷或過熱的極端溫度影響。在承重結(jié)構(gòu)允許的條件下，目前大面積的城市屋頂都可以建設(shè)溫室。工廠、倉庫、停車場和部分商業(yè)零售建筑的現(xiàn)有柱結(jié)構(gòu)（或者經(jīng)過加固以后），都可以支撐溫室建設(shè)（圖6）。新建筑可以在設(shè)計中增設(shè)屋頂溫室。如果能形成足夠的規(guī)模，溫室農(nóng)業(yè)可以解決氣候變化引起的部分問題，并擴大可供糧食種植的土地面積。

6 加拿大蒙特利爾Lufa Farms的屋頂溫室建造于現(xiàn)有倉庫結(jié)構(gòu)之上。目前有大量的屋頂可增建溫室，也可以在建設(shè)新的工業(yè)、停車、商業(yè)建筑時增建溫室。在城區(qū)種植食物可以減少運輸成本和尾氣排放，如果應(yīng)用于足夠多的建筑，這種設(shè)計能夠提升糧食供給總量This rooftop greenhouse belonging to Lufa Farms in Montreal, Canada was built on top of an existing warehouse structure.There are many hectares of rooftops with the potential to add greenhouses; and greenhouses can also be included when new industrial, parking, or retail buildings are constructed. Food grown in urban areas reduces the costs – and emissions –for transportation; and such designs, if adopted for enough buildings, can improve the over-all food supply

6 氣候危機如何影響城鎮(zhèn)化政策

數(shù)年后，部分土地需要昂貴的防洪或防火保護措施才能為人所用，現(xiàn)在仍然批準(zhǔn)這些土地用于城鎮(zhèn)化開發(fā)，將是非常嚴(yán)重的錯誤。用以保障糧食安全的農(nóng)業(yè)用地不宜城鎮(zhèn)化。潔凈水資源短缺的地區(qū)也不宜建設(shè)高耗水的項目。在現(xiàn)有社區(qū)加建和新城選址過程中，也要綜合考慮上述因素。所有的非建成區(qū)發(fā)展規(guī)劃，都必須包含氣候危機管理設(shè)計，許多符合過去城鎮(zhèn)化選址要求的地區(qū)，未來將不再適宜城鎮(zhèn)化建設(shè)。因為氣候已經(jīng)開始改變，21世紀(jì)中期的環(huán)境危機近在眼前，調(diào)整城鎮(zhèn)化政策已迫在眉睫。

注釋：

喬納森·巴奈特及其賓夕法尼亞大學(xué)同事馬蒂耶斯·布尤所著的新書Managing the Climate Crisis將于2022年由Island Press出版社出版。

圖片來源：

圖1 ? Flor!an根據(jù)知識共享署名3.0協(xié)議；圖2 ?2021 Google；圖3 ?新南威爾士州政府；圖4 ?2021 Google；圖 5 ? Ideaa.edu根據(jù)知識共享署名4.0協(xié)議；圖 6 ? Lufa Farms根據(jù)知識共享署名2.0協(xié)議。

（編輯/劉昱霏）

How a Changing Climate Will Transform Urban Design

Author: (USA) Jonathan Barnett Translator: XU Boqian

Predictions about the dangers created by climate change depend on assumptions about how successfully the nations of the world limit emissions of greenhouse gases into the atmosphere. However, all predictions are similar up to the middle of this century, because there has been so much greenhouse gas emitted already,especially in the last fifty years. More greenhouse gases continue to be added every year; and so far there has not been much progress in reducing the rate of accumulation. There is already enough greenhouse gas added to the atmosphere to create climate threats right now and bigger threats by 2050. Problems began much faster than scientists thought likely even a few years ago: rising tides along the coasts, more flooding along rivers, more extreme rain events, increased risk of wildfires,longer heat waves and shortages of food and fresh water.

The practice of urban design is already changing in response, and will be transformed by mid-century because the environmental context for designing cities will be so different.

Modern city design everywhere in the world has depended on the assumption that the natural environment would remain the same for decades,even centuries, and that the engineering profession can always remake the landscape in response to concepts about cities and their infrastructure.

Decisions about building along coasts and rivers, made without question only a few years ago,are beginning to look less safe. Dams, sea-walls,bridges and underground infrastructure that met all engineering requirements when they were built may now be at risk.

Places where land is levelled, or where lowlying land is raised with fill; places where streams are enclosed in pipes; places where almost all the land is covered by buildings or by pavement,places where prime agricultural land is becoming urban – the design decisions that are creating all these places may become unsustainable and need to be corrected.

Glass-walled buildings that need extensive artificial heating and cooling, building placements made without reference to air circulation,heavy dependence on cars and trucks for local transportation - all will need to be rethought.

What needs to be done to keep people safe from climate change now and in the future will be different from place to place. Future risks must be determined using the best scientific information,and responding to these risks with resilient designs for cities will be a central task for urban designers and planners, as well as architects, landscape architects, and engineers.

Rising sea levels can subject coastal areas to repeated flooding, and in a big storm the tidal surge can be more forceful, and extend much farther inland, than has ever been seen before. Increasing volumes of water in rivers can over-top flood-walls and possibly wash them away. Heavier rainstorms can overwhelm local flood management. Designing protections and possibly relocating people away from the most dangerous areas will be a priority task.

In some places more intense and frequent wildfires will also require protections, or people moving to safer places. Longer periods of extreme heat will make cities unhealthy and will require improved outdoor shade and air circulation, and heat-resistant buildings. Periods of drought and extreme heat can endanger water supplies, and cause crops to fail. Designing for food security will be a high priority.

China’s Urban Design Management Approach,adopted in 2017, offers a template for what will be needed: a national Management Approach for a Warming Climate covering a broad range of urban and landscape design issues, plus climate-specific requirements for planning, architecture, and engineering.

1 How Flooding Threats Affect Urban Design

The changing relationships between land and water will require new urban design approaches for developing areas, and redesigns for existing development.

1) Redesigning Waterfront Esplanades. One of the most important ways urban design improves cities has been recapturing waterfronts for public use as the need for industrial land along the edge of the water has diminished. Parks, pedestrian promenades, and waterfront destinations like restaurants have become widespread and very welcome improvements. But a warming climate will inevitably change the design of these esplanades and the way people use them. Rising sea-levels are already bringing higher tides and larger storm surges to the edge of esplanades in coastal cities.Waterfront parks along rivers will also see higher water levels, plus bigger floods from more powerful storm events. By mid-century all public waterfronts will need to be redesigned to accommodate higher water levels and also to help protect adjacent urban development from flooding. The esplanades will need to be both higher and stronger. Places which do not have esplanades now will come to need flood and surge protection, and a new kind of multi-purpose waterfront esplanade, combing public amenities and flood walls will often be the way to protect them. The challenge for urban designers will be to incorporate effective flood defenses while preserving and creating public access and amenities.

Most urban waterfront esplanades have been designed to bring people as close to the water as possible, often with boats moored right along the edge. Protecting cities from the changing climate will sometimes mean separating people from the water by introducing an intervening level of breakwaters or perhaps mangroves or other kinds of protective wetlands. A new understanding of ways to retain and manage floods could also move waterfront esplanades back from rivers to make room for an extended flood plain, part of what is meant by turning urban areas into sponge cities that manage floods by safely retaining the water until the flood danger goes down. Where flooding is periodic, waterfronts may be designed with two levels. The lower level can be designed to flood,and then be easily cleaned and reopened to the public, while a higher level is designed to remain permanently above the water and to protect the urban edge (Fig. 1).

2) Redesigning Public Spaces to Manage Water. Floods from heavy rainstorms can overwhelm a city’s drainage system, and more extreme rain events will be one of the consequences of a warming climate. The public open spaces in cities can be redesigned to become a flood management network, a green infrastructure which becomes a part of sponge city policies (Fig. 2). But existing public open spaces were usually designed and placed without reference to natural land contours and the flow of stormwater, so managing stormwater will have to become a major determinant in redesigning these spaces. There will often turn out to be missing connections that will have to be added to the open space system to make it effective for flood management. Private open spaces belonging to groups of buildings should also be redesigned and added to the system. In addition, the existing stormwater infrastructure will need to be evaluated,particularly where pipes that empty stormwater into rivers or the ocean will become blocked as water levels rise.

3) Making Infrastructure More Flood-Resistant. In addition to stormwater systems,underground transit systems, railways and highways along shorelines, the size and location of wastewater pipes, the stability and effectiveness of existing dams and floodwalls will also have to be evaluated and some are likely to require being modified or rebuilt to new design standards. This will be a massive undertaking and studies should begin right away.

4) Making Buildings More Flood-Resistant.Government regulations for buildings will need to be amended to make sure that structures are safe from flooding, especially if they are in locations that are not protected by flood walls. Heating and air-conditioning machinery, elevator hoist systems,and other equipment will have to be on roofs or on a high floor. Parts of buildings where people live or work will have to be located well above the floodplain, which can mean elevating streets, land, and buildings on fill, or raising individual buildings on columns. Existing urban areas at risk from flooding will need to be retrofitted or rebuilt. These kinds of changes in building regulations mean that architects, landscape architects, and urban designers will have to reimagine whole villages or districts of cities to keep people safe.

5) Incremental Removal of Communities That Cannot Be Protected. There will be some communities where flood protections for buildings and infrastructure will be impractical or too expensive, or where raising structures and continuing to provide infrastructure support will eventually become impossible. These places need to be identified, and plans made for people to be relocated in stages, with as little disruption to their lives as possible. By the time these places are no longer inhabitable, everyone should have moved away and the land returned to a nature.

2 How Wildfire Will Change Community Designs

Wildfire is a recurring natural process. It becomes a problem when people and property are in the way. Unlike threats from flooding, which will only continue to become worse, wildfire in forests and grasslands will eventually be self-limiting. Areas will burn; and regrowth can be more appropriate for a changed environment and less likely to burn again – at least for many years. But such large ecological changes will take a long time, and dangerous wildfire conditions are likely to persist through the middle of this century.

1) Designs that Separate Development from Wildlands. The best way to protect people and buildings from wildfire is to keep them separate.Permitting building in places surrounded by woodlands has always been a risk. But, in the past,when cycles of heat and drought were known and understood, people felt they knew what the wildfire risks were, and insurance was often available. But as warm seasons become longer, there is more time for insects to attack trees, and for heat and drought to dry out trees and grass. As plants become less well-adapted to where they are growing, they begin to die. A dry wildland with a lot of dead vegetation is only waiting for a spark – from lightening or from activities by people – for a fire to begin.

The wind can carry fires across open spaces,but only for a limited distance. When individual structures, or small villages, are surrounded by flammable wildlands, structures may survive if a sufficiently wide space is cleared around them.Development on the edge of wildlands can also be protected if there is a wide enough cleared space,called a fire-break, between the edge of the forest and the development. Places at risk for wildfire need to be redesigned to make them more separate.

A more complicated design problem will be to identify places that will be at risk from wildfire by mid-century, and redesign them to insure that people remain safe. Historic parks and woodlands that have long been part of cities and towns should be studied to see what changes may be needed.

2) Making Buildings and Communities Fire Resistant. Building regulations for places at risk from wildfire should require that construction materials for roofs and walls be fire-resistant. It is also necessary for window, door, and ventilation openings be designed so that embers or flames cannot enter the building. Decks, porches, and other structures connected to the building should also be fire-resistant, or kept well away from the main structure (Fig. 3).

3) Incremental Removal of Communities That Cannot Be Protected. As for places at risk from flooding there may be places where protections from wildfire will be impractical or too expensive.Plans will need to be made for people to be relocated in stages, with as little disruption to their lives as possible. This may be an urgent matter as wildfire risk can develop rapidly. By the time these places are no longer inhabitable, everyone should have moved away and the land returned to a nature.

3 How Heat Waves must Change City and Building Designs

Weeks and even months of extreme heat,with little relief, are becoming normal for cities that seldom if ever had experienced such hot weather. Using artificial cooling machines to moderate building climate indoors not only increases energy use, but the heat is transferred to the areas immediately around the buildings making the outdoor temperatures worse. Architects and city designers need to rediscover natural cooling techniques in use before air-conditioning, and these techniques need to be incorporated into the urban design and building regulations of places where summer temperatures are producing extended periods of extreme heat.

1) Designing Streets, Open Spaces, and Buildings to Facilitate Natural Ventilation. Streets and open spaces can be planned to facilitate ventilation by prevailing winds during the day and – especially important – at night, when cooler air can blow through a city and disperse accumulated heat. Natural ventilation can also be designed into buildings so that cooler air circulating above a city can be brought down into a building from ventilation towers, or cooler air can be let into the lower floors of a building at night, where it can push warm air up and out of the building through the same ventilation towers.

2) Shading Streets and Buildings. Extensive tree planting along streets has been shown to lower temperatures in dense urban areas, not only for people walking in the shade, but also in the surrounding area. In places which are too hot and dry for shade trees, shade structures can be built,perhaps by using a fabric on a metal frame (Fig. 4).

Buildings with glass-curtain walls are a mechanism for heating up the building interior.The heat-gain can be balanced by air-conditioning,but it causes greater energy use and transfers the heat into the surrounding city. Advanced glass technology can reduce heat gain, but external shade structures are a good alternative. They were a fashionable design concept in the middle of the last century, but sleek, reflecting towers have been preferred for a long while. It is time for designers and regulators to give priority to reducing heat-gain in buildings, particularly where extreme heat is an increasing problem.

4 Designing Land and Buildings when Fresh Water is Limited

Diminished rainfall in some areas is a product of a changing climate and is expected to become a more severe problem by mid-century.

1) Limiting Dust-Storms. Dust-storms are one symptom of drought conditions, and it may be possible to limit dust storms by anti-desertification measures, such as planting grasses to hold desert soil in place. Planting cover crops and limiting the amount of soil turned over when planting seeds can reduce wind erosion of cropland. Such measures already need to be adopted at a large scale in areas where drought as a problem, and such efforts need to be widely adopted by mid-century.

2) Regional Ecological Reclamation: China has been a leader in seeking to reclaim large regions from ecological degradation, including forest protection, sand control, and grassland conservation. A success that has attracted international attention has been the Loess Plateau Watershed Rehabilitation Project begun in 1994 with restrictions on where crops were planted, on grazing, and on tree-cutting, followed by extensive replanting. A substantial area has been brought back from dry, near-desert conditions to the green landscape shown in Figure 5. Ecological restoration at this scale can also increase the amount of rainfall, which further reinforces the greening of the landscape.

3) Using Less Water for Industrial Cooling.Power plants and other industries often draw fresh water from streams for their cooling systems,returning the water to the streams at a higher temperature and with the risk of contamination.A simple alternative, although more expensive to build, is to close the cooling system, with the same water recirculating after being cooled by evaporation on site. This method requires a substantial area for the cooling ponds, so the sites for these kinds of industrial installations will need to be much larger.

4) Conserving Irrigation Water. Agriculture requires large amounts of fresh water. Flooding fields is easy to do, and essential for rice cultivation,but flooding other kinds of crops means major losses of water to evaporation. Spray irrigation,where a sprinkler system covers a large area with artificial rain, also wastes a lot of water from evaporation or from irrigating the wrong places.The irrigation method which conserves the most water is to deliver it at ground level through perforated pipes. The design of the pipe system determines the arrangement of the crops being irrigated, with different pipe volumes and spacing for different crops.

5) Managing Drinking Water Supplies. Many urban pipe systems loose a substantial amount of their water to leaks. If system leakage is more than 10 percent, places with limited water supplies need to plan a program for repair and replacement.Similarly, many household appliances – and home and office cooling systems – use more water than they need to. Over time, replacements that use less water can make a substantial difference to overall consumption. Capturing rainwater for landscape irrigation can replace scarce drinking water for maintaining plantings around buildings, so that designs for residential and commercial landscaping need to take advantage of this option, with the flow of irrigation water pumped from cisterns that conserve water after it rains. Where demand is increasing faster than available water resources,these types of management are essential.

5 Planning for Future Food Shortages

The combination of increasing populations and changing growing seasons makes food shortages likely by mid-century even in countries that have stable food supplies now. As growing seasons change, crops can become less well-adapted to the places where they have been successfully cultivated for centuries. The climate in other places may become more suitable for these crops, but the soil conditions are likely to be different and it is not certain that crops can simply move to stay in synchronization with the most favorable climates for them. The alternatives for importing food may become unreliable as exporting countries keep more of their agricultural products at home because of their own food shortages.

1) Conserving Agricultural Land. Uncertainty about future food supplies is a powerful argument for conserving agricultural land, not just the best land, but all land available to grow crops or trees.The assumption that most land adjacent to urban areas can be urbanized needs to change right away.

2) Making More Use of Greenhouse Agriculture. Protecting crops with transparent structures of plastic or glass can prolong growing seasons and shield plants from excessive cold and, with shading devices, also from excessive heat. The vast acreage of existing urban rooftops can support greenhouses when the structure is suitable. Factories, warehouses, parking garages,and some retail buildings have column structures that can support greenhouses, or can be reinforced to support them (Fig. 6). New buildings can be designed with rooftop greenhouses. If organized at a broad enough scale, greenhouse agriculture can off-set some of the problems created by a changing climate, and add to the growing surfaces available to support the food supply.

6 How Climate Threats Will Change Urbanization Policies

It will be a serious mistake to permit urbanization of land that, in a few years, will require expensive protections from floodingor from wildfire - in order to remain usable.Agricultural land that will be needed for food security should not be urbanized. Places at risk of fresh-water shortages also should not be developed to uses that increase the demand for fresh water.These considerations need to be incorporated in procedures for expanding existing communities and for locating new towns. All plans for development in green-field locations will have to include designs for managing climate threats, and many places that met criteria for urbanization in the past will then be understood as places where urbanization should not take place. Because the climate is already changing and a mid-century climate crisis is only a few years away, urbanization policies need to be adjusted now.

Note:

Jonathan Barnett, and his University of Pennsylvania colleague Matthijs Bouw, are the authors of a forthcoming book, Managing the Climate Crisis, to be published by Island Press in 2022.

Sources of Figures:

Fig. 1?Flor!an used according to C.C. 3.0; Fig. 2 ? 2021 Google; Fig. 3? Government of New South Wales; Fig. 4 Image Capture 2018 ? 2021 Google; Fig. 5? Ideaa.edu used according to C.C. 4.0; Fig. 6? Lufa Farms used according to C.C. 2.0.