綠色基礎設施城市主義和氣候變化

（新西蘭）馬修·班博瑞 王昕欣

0 前言

氣候變化造成的環境影響對現有和擬建城鎮提出了許多挑戰。隨著氣候變化的到來，城市洪水、雨水污染和城市熱島效應已成為關鍵的全球問題。綠色基礎設施被認為是減輕城市化負面環境影響的有效工具，那么綠色基礎設施的概念可否用來增加城市應對氣候變化的韌性？

綠色基礎設施通常是由城市空間內的原生植被和水系統提供生態系統服務。作為一個術語，它在20世紀90年代首次被用于指代美國城市周圍的“綠道”或“綠道網絡”[1]。綠色基礎設施的多功能性和對建筑環境的潛在好處在世界范圍內被認可。科研人員、設計人員和政策制定者賦予了綠色基礎設施不同的定義[2]。最近的一個定義將綠色基礎設施的范圍擴大為“由各類空間尺度的城市區域內部、周圍和之間的多功能生態系統的所有自然、半自然和人工網絡組成”[3]。

許多城市已經嘗試使用綠色基礎設施的解決方案來緩解環境問題，尤其是城市洪水。為應對2011年洪水事件，哥本哈根市政當局制定了一項城市戰略，將公園用作洪水滯留區，并將街道重新規劃為泄洪通道。在哥本哈根HansTavsens公園的設計中，景觀設計師開發了一個綠色基礎設施系統，該系統包含一系列的下沉池和植物區，用以緩解社區洪水和凈化雨水。該項目創造了一個保護居民免受洪水侵襲的新生態系統，也為人們創造了新的社交空間[4]。

意大利為了應對空氣污染和洪水，設計了2個新公園來取代現有的鐵路基礎設施。米蘭北部和南部的2個鐵路站場被設計為綠色片區（green zone）和藍色片區（blue zone）。綠色片區可以凈化空氣污染物，降低盛行風帶來的城市熱量；藍色片區可以清潔雨水并改善生物多樣性。它們共同發揮綠色基礎設施的作用，以恢復城市生態并提供額外的休閑空間[5]。

人們越來越多地將綠色基礎設施視為減緩氣候變化對環境影響的一種方式。研究表明：綠色基礎設施可用于減輕城市洪水和雨水污染的影響[2]。作為雨水管理措施的綠色基礎設施通常是濕地、池塘、雨水花園、洼地、綠色屋頂和透水路面[6]。這些干預措施還有助于改善生物多樣性[7]、改變城市微氣候[8]和減少碳足跡[9]。

本文作者認為上述文章和案例研究將綠色基礎設施主要用作工程措施，即用本土植物和自然雨水系統等綠色基礎設施來替代傳統的城市道路和排水設施。實際上，與傳統基礎設施相比，綠色基礎設施的優勢還在于創造了新型交往空間。

要擴大綠色基礎設施的應用范圍來幫助建立城市韌性以適應氣候變化導致的環境問題，必須超越綠色基礎設施的傳統定義，即在不改變城市形態的基礎上，實現與傳統基礎設施同樣的功能。因此建議：擴展綠色基礎設施作為自然系統的能力，在當代城市的設計過程中構建可持續的基礎設施。

然而，我們面臨一種當代城市思維的通行模式，即所謂的“緊湊型城市”。這種城市理念提出了許多值得稱道的模式，解決了對汽車的依賴、工作與家庭的分離、公共空間不足等明顯可識別的城市問題。

但這種城市理念的一個關鍵問題是：看似理想化的城市結構，其建筑物、街道和開放空間都是堅硬的、不透水的表面。缺乏開放綠地會減弱吸收降雨的能力并加劇城市氣溫上升，這意味著當代緊湊型城市本身將加劇因氣候變化帶來的環境影響。

而要擴展綠色基礎設施的理念，必須要重新思考未來城市的空間形態。需要將城市重新想象為一個更加開放的結構，具有能夠吸收雨水并符合自然水文系統運行規律的區域。筆者建議的綠色基礎設施理念前景是將城市結構建設為超綠色基礎設施。

文章的第一部分將介紹基于流域的城市規劃方法。該理念使用原始水文系統作為設計新型城市綠色基礎設施的主要驅動力。第二部分將介紹一個三步驟設計過程以優先考慮城市綠色基礎設施的創建，并將描述一組有助于創建氣候變化響應的策略。通過位于新西蘭奧克蘭韋努阿佩的一個新城案例，展示如何用這種方法創建城市綠色基礎設施以應對多樣的氣候變化，同時創造新的城市形態并確保預期的房地產投資回報。最后，反思了在氣候變化的挑戰下，城市綠色基礎設施的設計對中國城市未來發展的影響。

1 設計過程

為了展示如何將綠色基礎設施的基本理念擴展到設計新的城市形態以適應氣候變化的影響，筆者將介紹一個新城開發的推測性設計過程，并通過一個新西蘭的案例研究展示該設計方法在設計實踐中的應用。

要了解氣候變化對城市的影響，必須理解3件事：1）氣候變化的影響是什么；2）不同類型的城市發展策略有哪些；3）可能的補救方法是什么。通過結合這3個領域的知識，可以建立一個應對氣候變化、具有韌性的城市綠色基礎設施系統。

1.1 步驟一：調查

城市綠色基礎設施設計過程的第一步是在一個可衡量的系統內定義氣候變化對特定方面的影響。水文流域[10]是一個通過觀察水文循環的可測效果，將特定的景觀形態（流域）與城市形態聯系起來的系統。第一步是建立調查清單。該清單包括流域的定義，開發場地及流域的位置和邊界。通過航拍照片、流域地形、植被和水文，特別是地表徑流路徑，進一步確定城市開發場地在流域內的位置。特別需要分析流域內透水地表與不透水地表的比率。了解流域的這一要素很重要，因為城市開發場地能夠通過透水地表吸收氣候變化導致增加的降雨量。

1.2 步驟二：發展

城市綠色基礎設施設計過程的第二步涉及對從局部場地設計到宏觀規劃發展機制的理解，可以通過經濟指標來衡量開發過程。流域內的城市發展潛力可以通過多種方式衡量。單個地塊的經濟回報可以用簡單的開發強度來理解，即總建筑面積（gross floor area,GFA）和容積率（floor area ratio, FAR）[11]。簡單地說，單個場地的總建筑面積與建筑基底面積的比例關系是由多個要素決定的，通常是由地方當局的設計導引和開發收益決定。

筆者建議如果將綠色基礎設施納入城市設計過程，需要調整容積率指標：用增加透水地表的面積來換取建筑高度的增加。由此可以提高開發場地對氣候變化的適應能力。

一個較大的城市場地的發展潛力，無論是新區開發還是舊城改造，都可以通過結構規劃①和詳細規劃來展示。這兩類規劃可展示場地在不同規劃層次的發展潛力：從簡單的用地分區布局到詳細的建筑分布布局。

應對氣候變化的韌性與城市發展規劃的關系可以從幾個方面進行分析。對于新區開發、水文的影響可以通過簡單地測量開發前與開發后透水和不透水地表的比率來理解。這一比率可以通過很多水文軟件來計算，這些水文軟件可用于演示氣候變化對結構規劃開發的影響，以及對場地水文平衡的影響。

氣候變化對城市規劃的多重影響可以通過規劃圖與場地現狀水文圖的疊加來揭示。例如，在疊加圖中，規劃中的部分用地會切斷地表徑流路徑而阻滯洪水排放，或部分用地位于海平面上升的淹沒區。這些問題有助于我們理解規劃與環境的沖突。通過使用推理公式法[12]以及幾個軟件程序，也可以理解不透水地表增加對環境的影響程度。

構建適應于氣候變化的城市綠色基礎設施的設計過程，首先應將城市發展置于水文流域內。明確場地現有環境條件以及氣候變化對水文系統的影響。將開發場地——從單個場地到結構規劃——與流域水文系統進行疊加，可以繪制和測量不同城市形態對環境的影響。

1.3 步驟三：韌性

一旦了解了氣候變化對新城發展的影響，就可以探索幾種修復策略來幫助構建城市綠色基礎設施。開發新城市綠色基礎設施形態的設計方法通常包含兩類：景觀類和建筑類。其中一些方法是由低影響城市設計和開發（low impact urban design and development,LIUDD）技術衍生出來的[13]。LIUDD的目標是：充分利用現有基礎設施，通過選址使開發的影響最小化，使開發與生態系統的承載能力相匹配，并最大限度地減少流域內的能量投入和產出。這些目標是通過采取特定策略達到的：保護開發場地現有的敏感區域來保護陸地和海洋生物多樣性；盡可能地維持流域的自然水文；恢復和保護自然景觀，減少或控制開發場地的污染物；以及開發新的城市形態，即通過簇群化布置建筑項目來幫助保留或創造透水空間。

這些技術可以使用地理信息系統（GIS）軟件進行建模。要保護場地現有的水文格局：需識別從流域上游穿過開發場地的地表徑流路徑，并運行緩沖命令以確定須保護的河岸廊道；還可以在濱海岸線或河流邊緣建立緩沖區來保護沿海地區。這些設計策略能發揮多種功能：例如，地表徑流路徑緩沖區可用于泛濫洪水的輸送和滯留；還可以沿地表徑流路徑種植本土植物，以幫助促進蒸騰作用并降低城市熱島效應；地表徑流路徑緩沖區網絡還可設置雨水處理設備（如濕地），以處理來自更大流域范圍的雨水[14]；濱海岸線的緩沖區有助于設計和定位防海洪的軟屏障。

以上修復技術對流域的凈影響可以通過重新計算透水與不透水地表的比率來衡量。通過以上三步驟的設計，構建更加開放和綠色的城市綠色基礎設施，并通過多種修復機制幫助城市建立抵御氣候變化的能力。

這種新的城市綠色基礎設施對傳統房地產項目的影響是：需要解決如何分布建筑面積以滿足項目的經濟需求。這可以利用LIUDD策略的建筑項目簇群化布置實現。將總建筑面積重新布局，即在滿足環境修復規劃的前提下重新配置建筑基底，可以實現原始房地產投資的經濟回報。將重新規劃的建筑基底導入ArcGIS中建模，在三維空間中通過拉伸命令將建筑基底拉伸成3D建筑模型。

2 案例研究

本研究以新西蘭奧克蘭韋努阿佩的新城市開發項目的提案為例，演示如何設計新的城市綠色基礎設施，展示三步驟的城市綠色基礎設施設計過程在應對氣候變化造成的城市環境問題的適用性，以及改善這些問題的方法。

第一步為確定新的城市發展可能產生哪些環境問題。通過2個尺度的流域研究，確定了主要的環境問題是洪水量的增加和洪水對水質的污染，及對現狀水文系統和接收環境的危害。

第二步為確定開發分區及開發對流域的環境影響。應用推理公式法[12]來了解開發前后流域內透水與不透水地表的比率對雨水和洪水產生的影響。這一步的策略是防止污染的雨水和洪水進入現有水文網絡。具體技術是在現有的溪流兩側生成緩沖區，可通過GIS制圖和分析來識別現有的水文網絡、河流和地表徑流路徑，然后利用ArcGIS中的緩沖命令在每個地表徑流路徑和河流周圍建立保護區[15]。此操作的效果還在于增加了透水地表的面積。

第三步是簇群化布置城市形態。為保證現有的水文系統和規劃的綠化緩沖區，將不可避免地損失開發建筑面積。為確保預計的房地產項目不會產生經濟損失，可將開發建筑面積簇群化布置為新的城市形態[16]。韋努阿佩案例研究的城市設計結果是將“缺失”的建筑面積聚集在位于河流系統與濱海交匯處的公寓樓。

2.1 韋努阿佩

韋努阿佩是新西蘭奧克蘭西部規劃的新城區（圖1），位于上懷塔瑪塔港的南側，其西部邊界為布里格姆河，南部和東部邊界分別為16號、18號國道；場地大部分平坦，平均海拔約25 m以上；主要建設用地為韋努阿佩機場。

1 韋努阿佩區位Whenuapai location

2.1.1 韋努阿佩場地分析

1）水文。韋努阿佩可分為8個主要流域（圖2-1），由布里格姆河、拉拉瓦拉河和懷阿羅黑河等多條河流劃分，并經10條河道排入海港。韋努阿佩年平均降雨量為1 333.5 mm，月平均降雨量為111.1 mm。最干燥月份1月的平均降雨量為79.3 mm；最潮濕月份6月的平均降雨量為147.8 mm。

2-1 韋努阿佩流域Whenuapai catchments

2）坡向和坡度。韋努阿佩的坡向主要是北向，沿溪流廊道兩側的部分用地為東西朝向（圖2-2）。大部分場地的坡度平坦（0～5°）；而沿溪流廊道的部分用地坡度為5°～16°不等（圖2-3）。

2-3 韋努阿佩坡度Whenuapai slope

2-2 韋努阿佩坡向Whenuapai aspects

3）植被。該場地最初由新西蘭的本土沿海森林覆蓋。韋努阿佩流域沿海邊緣的典型植被特征屬于Kowhai-Kotare港海岸線生態系統[17]，優勢樹種有Metrosideros excelsa、Sophora microphylla、Dysoxylum spectabile、Vitex lucens、Agathis australis、Corynocarpus laevigatus和Alectryon excelsus。灌木種類包括Pittosporum crassifolium、Astelia chathamica、Pittosporums tenuifolium和Myoporum laetum。

2.1.2 韋努阿佩結構規劃

奧克蘭正在經歷城市快速發展的時期。預計未來20年將有超過100萬人口的增長。城市快速增長造成了嚴重的住房短缺。韋努阿佩毗鄰16號國道 ——奧克蘭西部城市增長廊道的一條重要高速公路，且靠近新的西北購物中心，毗鄰霍布森維爾住房開發項目（近年來成功的新城開發項目），使韋努阿佩成為未來城市發展的下一站。為了應對奧克蘭面臨的城市壓力，奧克蘭市議會為韋努阿佩制定了城市結構規劃，以幫助構思未來城市發展的形態[18]。根據與基礎設施的鄰近度，該結構規劃對可用土地進行了區劃：工業用地和公寓區位于主要交通路線16號和18號國道附近；較低密度的住宅區靠近懷特瑪塔港；大地塊的單層住宅被規劃到沿海邊緣；而更密集的住宅（中等密度）被劃在沿海邊緣和工業區之間（圖3）。

3 韋努阿佩官方規劃Whenuapai council plan

而擬議的結構規劃將導致一系列環境問題，包括雨水污染和洪水增加，這些問題將因氣候變化的影響而加劇。為了探索這些影響的后果，本文作者在韋努阿佩大流域內選擇了一個子流域——拉拉瓦拉子流域，作為案例研究的范圍。通過對拉拉瓦拉子流域的水文分析來理解擬議規劃的城市發展后果，并制定策略以修復其對環境的影響。

2.2 拉拉瓦拉子流域

2.2.1 步驟一：拉拉瓦拉子流域調查

324 hm2的拉拉瓦拉流域位于韋努阿佩流域北部（圖4）。該流域地勢相對平坦，北面以懷特瑪塔港為界，西面是布里格姆河和皮托伊托伊流域，東面是韋努阿佩村和機場，南面是16號和18號國道的交匯處（圖5）。

4 拉拉瓦拉子流域的位置和邊界Rarawara location and boundary

5 拉拉瓦拉子流域現狀圖Rarawara sub-catchment existing condition

1）植被。該流域的主要植被是草地，也是流域的鄉村經濟產物。其他植被包含住宅區庭院的裝飾性花園植物以及小型園藝和果園街區中的防護林樹種。

2）水文。該流域的主要溪流均匯入拉拉瓦拉河。拉拉瓦拉河大致呈南北走向，將整個流域一分為二。拉拉瓦拉子流域又可劃分為3個子流域。拉拉瓦拉河河口與懷特瑪塔港相連，從腹地到海濱拉拉瓦拉子流域兩側都有較小的溪流（圖6）。

6 拉拉瓦拉地表徑流Rarawara overland flow

3）坡向和坡度。拉拉瓦拉流域的坡向大多為北坡，沿溪流廊道的兩側有部分用地為東西朝向（圖7-1）。場址大部分坡度平坦，為0～5°，尤其是機場用地（圖7-2）；而沿著溪流兩側的廊道坡度為5°～16°不等。

7-1 拉拉瓦拉坡向Rarawara aspects

7-2 拉拉瓦拉坡度Rarawara slope

4）土地使用。該流域內的土地用途分為2類：第一類為郊區住宅用地，包括大地塊住宅、北部沿海住宅以及機場西部的小地塊住宅；第二類為鄉村用地，由鄉村生活方式街區②和小型園藝和果園街區組成。

5）透水/不透水比率。現有的拉拉瓦拉流域面積為324.175 3 hm2。由于其主要是鄉村用地，該流域主要由透水地表構成，總透水地表面積為220.026 5 hm2；不透水地表面積由道路（81.842 8 hm2）和建筑物（20.100 4 hm2）組成，總不透水地表面積為101.943 2 hm2。得出透水與不透水的比率為2∶1（圖7-3）。

7-3 拉拉瓦拉透水和不透水地表Rarawara pervious/impervious surfaces

2.2.2 步驟二：拉拉瓦拉子流域發展

1）拉拉瓦拉結構規劃。奧克蘭市議會的韋努阿佩結構規劃將拉拉瓦拉流域規劃為4個住宅區和1個工業區。最靠近海岸的地區劃為低密度單層住宅區，沿海岸邊緣約100 hm2。每500 m2規劃一個住宅單位，可提供2 008戶住宅和50 hm2的不透水表面。沿海地區還規劃了一個82 hm2的中等密度住宅區，如果每300 m2規劃一個住宅單位，可安排2 743戶住宅，提供61 hm2的不透水表面。其余區域為工業或商業區，在機場區以東有2個公寓區。同時擬建3個公園，總面積約35 hm2。按照這一規劃布局，道路以及擬建和現有的房屋構成了212 hm2的不透水表面（圖8）。

8 拉拉瓦拉官方結構規劃Rarawara council structure plan

2）拉拉瓦拉子流域環境問題。隨著新住宅和相關基礎設施的建設，現有場地的水文格局將發生不可逆轉的改變；隨著沉積物的增加，徑流也會增加，這將增加上懷特馬塔港已經很高的沉積物污染程度，徑流也將受到道路污染物和屋頂碎屑的污染。

在奧克蘭市議會的結構規劃中，拉拉瓦拉流域的不透水地表面積將顯著增加。現狀拉拉瓦拉流域總面積為324.175 3 hm2。透水地表為規劃綠地，總透水地表面積為35.423 0 hm2。不透水地表由道路（81.842 8 hm2）和建筑物（206.909 5 hm2）組成，總不透水地表面積為288.752 3 hm2。得出透水與不透水地表的比率為1∶8。

如果按此規劃實施，那么這種高度不透水的發展結果是大量受污染的雨水徑流將排入海港，加劇洪水泛濫。計算新結構規劃下的流域雨水排放量，可采用推理公式法[12]（計算建設一個儲存和處理濕地所需的容積，采用TP10[19]）。通過推理公式法計算得到：2年一遇的徑流排放流量將為5.95 m3/s，此徑流所需的儲存和處理濕地面積為32 140.04 m3；10年一遇的徑流排放流量為8.71 m3/s，所需濕地的存儲量為47 019.68 m3；100年一遇的徑流排放流量為13.95 m3/s，所需的濕地存儲量為75 350.53 m3。

3）拉拉瓦拉流域環境修復。為了改善城市化對沿海水域的環境影響，有必要了解流域的水文行為。首先通過ArcGIS制圖確定場地所在流域的結構、形狀和大小，這些數據可以轉換為一系列的制圖過程，以顯示流域邊界和地表徑流路徑網絡。通過制圖過程，可以確定流域的大小、透水與不透水地表的比率。然后，通過推理公式法預測場地及周邊增加的降雨徑流量。具體方法為：計算新規劃住宅的建筑基底總面積，這部分面積為增加的不透水地表面積，進而計算出增加的雨水徑流量。一旦建立了住房密度與透水/不透水地表比率的聯系，就可以調整住房密度和透水/不透水比率的關系，以保證更大的滲透率，同時確保計劃的住宅戶數保持不變。

2.2.3 步驟三：拉拉瓦拉子流域韌性

可以通過減少不透水地表的面積來改善因雨水排放增加而造成的環境破壞；道路和住房等基礎設施的拆除也將增加透水地表的面積，從而提高場地吸收雨水徑流的能力。

1）景觀。增加流域透水地表的一種方法是通過在河流和地表徑流路徑周圍建立至少寬25 m的緩沖區來保護和增強現有的河流網絡；保護沿海邊緣是另一項重要的環境措施，30 m的沿海緩沖區將提供43 hm2的用地（圖9-1）。這兩項措施使流域內的透水地表面積增加了128 hm2。這種干預措施還可以增加沿溪流廊道和為海濱邊緣開發新公園系統（圖9-2）。

9-1 拉拉瓦拉地表徑流緩沖區和沿海緩沖區Rarawara buffered OLFP and buffered coastal edges

9-2 拉拉瓦拉綠地系統Rarawara green space syste

為實現這兩項措施，需要改變住房建筑基底，即將低密度區從100 hm2減少到23 hm2，并將中密度區從82 hm2略微減少到74 hm2。

2）拉拉瓦拉子流域城市設計。要滿足增加透水地表和減少雨水排放量的目標，意味著住宅數量的損失。根據奧克蘭市議會的結構規劃，流域內的低密度住宅數量為2 008戶，中密度為2 743戶，合計4 751戶（無高密度住宅）。為擴大透水地表面積，低密度區的住宅數量將減少到473戶，中密度區的住宅數量將減少到2 471戶，住宅數量的缺口為1 807戶。

解決這種住房短缺的一種方法是用公寓代替缺失的低密度住宅。此方案將增加1 468戶公寓（高密度住宅），將總住宅戶數提高到4 412戶。通過使建筑物更密集或更高來增加公寓數量，可以彌補1 807個住宅量缺口甚至更多，從而提供更好的房地產投資回報（圖10）。

10 拉拉瓦拉新的總體布局Rarawara new master plan

新公寓可以位于現有河口周圍的沿海地區。在低密度區域內8.8 hm2的用地內規劃2個高密度公寓區（圖11）。

11 拉拉瓦拉城市設計效果圖Rarawara urban design perspective

透水/不透水比率：在新規劃的用地布局中，拉拉瓦拉流域的總面積為324.175 3 hm2，其中透水地表的面積為128.001 0 hm2，不透水地表由道路（65.928 9 hm2）和建筑物（130.235 3 hm2）構成，總不透水地表為196.164 2 hm2，得出透水與不透水地表的比率為2∶3。

3）拉拉瓦拉子流域徑流。使用推理公式法，新透水地表產生的2年一遇徑流的排放流量為29 304 m3，相比之下，原址的排放量為26 468 m3，而奧克蘭市議會的結構規劃則為32 140 m3；在10年一遇的徑流排放量計算中，新規劃的排放量為42 871 m3，原址的排放量為38 722 m3，而奧克蘭市議會結構規劃的排放量為47 020 m3；在100年一遇的徑流排放中，新規劃的排放量為68 702 m3，而原址排放量為62 053 m3，奧克蘭市議會結構規劃的排放量為75 351 m3（表1）。

表1 拉拉瓦拉流域徑流Tab.1 Rarawa Catchment Run off m3

2.3 新綠色基礎設施城市設計過程的影響

2.3.1 設計過程的環境影響

1）溪流系統。新規劃的水文網絡周圍的緩沖區保證了溪流廊道的寬度來重新種植本地物種；該區域還可以用于放置結構性雨水清潔設施（特別是濕地和雨水花園）。這個溪流帶還可以加深從沿海岸邊緣到腹地的聯系，并創造一個生態廊道。

在新濱河區附近規劃的住宅區也將有助于提升房地產價值。新水網公園的邊緣設置中等密度的住宅中，業主可以欣賞到水景和原生植被景觀。新濱河區以及從海岸到腹地的連接為場地中部的業主提供了通達海岸的機會。

2）沿海地區。建立沿海緩沖區將保護該地區的關鍵環境，既可以恢復和保護關鍵的河岸生態，也可以減輕該地區海平面上升造成的破壞。

2.3.2 城市設計

在沿海及河流水文網絡周圍建立保護性緩沖區將提高拉拉瓦拉流域吸收降雨的能力，避免增加進入懷特瑪塔港上游的徑流，并減緩和減輕洪水。為確保達到相同的經濟回報（按照奧克蘭市議會結構規劃的規定建造相同數量的住宅戶數），可建造更多建筑基底較小的公寓來彌補減少的中低密度住房。其強調了獨特的沿河景觀：多層公寓樓穿插在底層的住宅和庭院景觀中。

2.3.3 韋努阿佩流域拉拉瓦拉案例研究的環境影響

新的城市綠色基礎設施規劃（圖10）展示了如何通過建立緩沖區來保護海岸線和溪流廊道。這一設計有3個成效。1）植物緩沖帶具有保護水文網絡的作用，可以清潔受污染的雨水和洪水，保護河流的水質。2）沿水文網絡規劃的綠地系統增加了透水地表的比例，確保更多的降雨能夠被透水地表吸收，這一新綠色基礎設施網絡的社會效益是建立了一個連接腹地和海岸的新路徑和公園系統。3）原規劃中被新的河流和河流緩沖區網絡取代的建筑面積，在新規劃中由河流網絡與海岸交匯處的公寓塔樓彌補。隨著氣候變化對環境的影響越來越持久，所有這些措施都將有助于建立未來的韌性。

3 結論

氣候變化將對城市環境產生破壞性影響。在完全了解氣候變化的影響力之前，綠色基礎設施在實踐中往往被用作傳統基礎設施的替代品，即用混合生態結構取代工程性結構。筆者認為，綠色基礎設施概念發展的方向是考慮將城市設計為超綠色基礎設施。也就是說，將城市本身嵌入一個更大的生態系統中。要針對性地解決氣候變化對城市的影響，必須轉變傳統理念，通過流域規劃、GIS制圖和標準水文計算來改變設計城市的方法。并將這些方法應用到城市設計中，既尊重和利用了現有水文系統，設計出新型的城市綠色基礎設施系統，又可以創造出更加開放、綠色的城市形態。我們認為，用綠色基礎設施引導城市設計，將有助于創造更安全、更具韌性同時更具社會效益的城市。

本研究突破了傳統的綠色基礎設施方法在適應氣候變化方面的局限性。筆者提出的綠色基礎設施城市主義理念探索了綠色基礎設施的新概念。這一理念可充分發揮綠色基礎設施的潛力：不僅形成一個能吸收更多雨水的綠色網絡，而且為新的城市形態建立一個超綠色的開放結構。這種方法將綠色基礎設施的設計推到了城市設計過程的最前沿，從根本上轉變了傳統綠色基礎設施的地位：即從后城市建設的補救措施轉變為規劃前的設計出發點。

本研究使用的方法是基于流域的方法，它使用水文流域作為分析單元來捕捉氣候變化的全部水文影響。該城市綠色基礎設施設計過程為設計師提供了一個有效的工具來識別新的城市發展可能產生的環境問題。設計技術如增加透水地表、保護現有水文網絡和簇群建筑形態等，為從事新城開發工作的設計師提供了易于遵循的指南。

本研究以新西蘭韋努阿佩的城市發展為例，展示了這種城市綠色基礎設施設計方法如何幫助設計師識別韋努阿佩流域和拉拉瓦拉子流域內的水文模式。設計過程展示了綠色基礎設施網絡是如何通過識別水文模式形成的，以及綠色基礎設施系統如何引導城市形態的設計。由此產生的總體規劃優先考慮氣候變化適應策略，同時不影響建筑項目和房地產回報。

隨著未來氣候變化的影響不斷升級，本研究提出的城市綠色基礎設施的概念將拓展綠色基礎設施的傳統認知及其解決氣候相關問題的潛力。基于流域的設計過程及相關技術為我們改變設計新城的方式提供了更多的可能性，使它們能夠適應氣候變化的持續影響。雖然研究對象位于新西蘭，但我們認為綠色基礎設施城市主義的概念和基于流域的設計方法非常適用于在中國各地的城市中建立對氣候變化影響的抵御能力。

注釋(Notes)：

①結構規劃是新西蘭的一類規劃層次，相當于中國的分區規劃：在城市片區內用不同色彩劃分不同的用地布局。

②新西蘭農村的典型用地類型。每個地塊以農場為主，住宅占很小一部分用地。

致謝：

感謝朱凱文協助修改GIS圖紙。

（編輯/王一蘭）

Green Infrastructural Urbanism and Climate Change

(NZL) Matthew Bradbury, WANG Xinxin

0 Introduction

The environmental effects caused by climate change poses many challenges to the viability of both existing and proposed towns and cities.Urban flooding, stormwater contamination and urban heat island effect have become critical global issues with the advent of climate change. green infrastructure is considered an effective tool in mitigating the existing negative environmental impacts of urbanism, can the concept of GI be extended to help build resilience to the effect of climate change?

Green infrastructure is generally understood as an ecosystem service provided by native vegetation and water systems within urban spaces.As a term, it was first used in the 1990s to refer to “greenways” or “greenways network” around the USA cities[1]. In recognition of its multiplefunctionality and potential benefits to the built environment, green infrastructure was promoted worldwide, and was given different definitions by researchers, practitioners and policy-makers[2].A recent definition broadens the scope of green infrastructure as “comprise of all natural, seminatural and artificial networks of multifunctional ecological systems within, around and between urban areas, at all spatial scales”[3].

Many cities have made attempts to mitigate environmental problems, especially urban flooding, with GI based solutions. In response to the Copenhagen flood event of 2011, the civic authorities developed an urban strategy to use parks as flood detention zones and replanned streets as conveyance corridors. In the design of Hans Tavsens Park, Copenhagen the landscape architects developed a green infrastructure system that consists of chains of sunken pools and planting, to ease neighbourhood flooding and purify stormwater.The project created a new ecosystem that protects residents from flooding, and generated new social spaces for people to enjoy[4].

In Italy, responding to air pollution and flooding, two new parks have been designed to replace existing railway infrastructure. Two railway yards to the north and south of Milan have been designated as a green zone and a blue zone. The green zone purifies air pollutants and reduces urban heat brought by the prevailing wind; the blue zone cleans stormwater and improves biodiversity.Working together, they act as green infrastructures to restore urban ecology and provide extra recreational space[5].

Green infrastructure is increasingly being thought of as a way to mitigate the environmental impact of climate change. Research suggests that green infrastructure can be used to mitigate the effects of urban flooding and stormwater contamination[2]. In the context of stormwater management, green infrastructure is usually presented as wetland, ponds, rain gardens, swales,green roofs, and pervious pavements[6]. These interventions can also help improve biodiversity[7],modify urban microclimate[8]and reduce carbon footprints[9].

We suggest that these writings and case studies position GI as primarily an engineering practice,substituting the conventional urban infrastructure of roads and drains with a green infrastructure such as the recreation of indigenous planting and the provision of natural stormwater systems. The use of this infrastructure as a new kind of social space is an added bonus that can’t be achieved with a traditional engineering infrastructure.

However, we suggest that to expand the world of GI today, to help build urban resilience to the serious deprecation of climate change, we will have to move beyond the conventional definition of green infrastructure as a system that will do the same task as conventional infrastructure while retaining the existing urban form. We suggest that we need to extend the insights that GI has given us the ability of a natural system to help build sustainable infrastructures to the actual design of the contemporary city.

It is here that we are confronted by the popular model of contemporary urban thinking which is sometimes described as, “the compact city”. This urban ideology puts forward a number of laudable urban tropes to address clearly identifiable urban problems such as the reliance on cars, the separation of work and home, the lack of public space and so on.

We suggest that one critical problem with this urban ideology is that the desired city structure, that is the building, streets, and open spaces are all hard,impervious surfaces. The lack of open green space that can absorb the expected increase in rainfall and mediate the rise in temperatures means that the contemporary compact city form will itself exacerbate by the environmental effects of climate change.

We suggest that we need to extend the ideas of GI to include rethinking the actual form of the future city. We need to rethink the city as a more open structure with zones to absorb water and allow natural hydrological systems to operate. We suggest the future of GI thinking is to establish the urban fabric as a supra green infrastructure.

The first part of this paper will introduce the idea of a catchment-based approach to urban planning. This uses the original hydrological system as the primary driver for the design of a new urban green infrastructure. The second part of the paper will present a three-step design process to prioritise the creation of an urban green infrastructure. A set of techniques that facilitate design response to climate change will be described. A greenfield site in Auckland, New Zealand at Whenuapai,will be used to demonstrate how this approach can create an urban green infrastructure that addresses multiple climate change events with a new urban form that still ensures the expected real estate return. The paper closes with a reflection on the urban green infrastructure design and its implications for city development in China that faces the challenges of climate change.

1 Design Process

To demonstrate how the key ideas of green infrastructure could be expanded to encompass the design of a new urban form to become resilient to the effect of climate change, we will outline a speculative design process for a new urban development site and how this design methodology might work in practice with a New Zealand case study.

To understand the effects of climate change on our cities we have to understand three things;firstly what will be the effect of the climate change,secondly what are the different kinds of urban development, and lastly what are the possible remediable techniques. By combining these three areas of knowledge we can develop an urban green infrastructure that will help build resistance to the effects of CC.

1.1 Step One: Inventory

The first part of an urban green infrastructure design process is defining the effect of a particular aspect of climate change within a measurable system. We suggest that the hydrological catchment[10]is a system that connects a specific landscape form, the catchment, with an urban form through measurable effects from the observation of the hydrology cycle. The first step is to build an inventory. The inventory consists of, the definition of the catchment, the location and boundaries of the development site, and the location and boundaries of the catchment. The placement of the urban development site within the catchments is further defined through aerial photos, the topography of the catchment, the vegetation,and the hydrology, in particular the overland flow paths. Of particular interest is the ratio of pervious to impervious surfaces within the catchment.Understanding this part of the behavior of the catchment is important as it is through the pervious surface that urban development site is able to absorb the increased rainfall that will be brought by climate change.

1.2 Step Two: Development

The second section of the urban GI design process is concerned with an understanding of the mechanics of the urban development process from the individual development site to the master plan. Understanding this process gives an ability to measure the development process through financial metrics. The urban development potential of a site within a catchment can be measured in several ways. The financial return of the individual site can be understood with simple development ratios, the gross floor area (GFA) and the floor area ratio (FAR)[11]. Simply speaking, the relationship of the individual development site to the building footprint can be manipulated in different ways according to several external criteria, typically, local authority guidelines and the development yield or return.

We suggest that the adoption of an urban green infrastructure design process can be made through the manipulation of the FAR provision to increase the amount of pervious surface in exchange for an increase in the building height.Thus, increased resilience to the effect of climate change can be made on the single development site.

The development potential of a larger urban site, either green field or brown field, can be understood through the development of structure plans and master plans. These show how a site might be developed to different degrees; from simple zoning layouts to detailed infrastructure layouts with building distribution diagrams.

The implication for building resilience to climate change for the urban development plan can be analysed in several ways. For a green field site,an understanding of the hydrological implications of a new development can be understood by simply measuring the ratio of permeable and impervious surface for a development site before development and post development. There is a range of different hydrological software that can be used to demonstrate how the hydrological balance of a site will be affected by the impact of climate change on the structure plan development.

The impact of climate change on a more sophisticated masterplan can be tested by superimposing the plan over the existing site inventory. Some of the environmental implication of the master plan can be understood in the way the proposed urban development might,for instance, block an overland flow path, thus preventing the conveyance of future flooding,or the way a development might be flooded by sea level rise. The implication of an increase of impervious surfaces can also be understood through the use of the rational method[12]as well as the use of several software programmes.

Constructing an urban green infrastructure design process that will build resilience to the environmental effects of climate change starts by placing urban development within a hydrologic catchment. In this way the examination of the existing environmental conditions of the site and the impact of climate change on the hydrological system, can be inventoried. By placing the development site, from an individual site to a structure plan within the hydrological catchment,the implication of the different urban forms can be both mapped and measured.

1.3 Step Three: Resilience

Once the effects of climate change on a new urban development are understood, several remediation strategies can be explored to help build an urban green infrastructure. These can be divided into two parts, landscape and architectural.Into these categories fall the actual techniques used to develop the shape of the new urban green infrastructure. Some of the techniques that can be used are derived from LIUDD techniques[13]. The LIUDD goals and techniques are: making the best use of the existing infrastructure, minimizing the effects of the development through site selection,matching the development to the carrying capacity of the ecosystem and minimizing the energy inputs and outputs within the catchment. These goals are developed through the use of specific strategies:protecting terrestrial and marine biodiversity through protecting existing sensitive areas on the development site; trying to maintain the natural hydrology of the catchment; reducing or containing contaminants on the development site through the restoration and protection of the natural landscape;and developing new kinds of urban form to help retain or create pervious space by clustering the building programme.

These techniques can be modelled using GIS software. Protecting the existing hydrological pattern of the site can be achieved by identifying the overland flow paths that run through the development site from the greater catchment and using the buffering function to ensure a protected riparian corridor. The littoral can also be protected by establishing a buffer zone to the harbour/river edge. The design consequences of these operations are varied, for example, the buffered overland flow path (OLFP) could be used for pluvial flooding conveyance and detention. The OLFP could also be planted with indigenous vegetation to help encourage evapotranspiration and lower the urban heat island effect. The buffered OLFP network could also be used to locate stormwater treatment devices such as wetlands to treat stormwater from the larger catchment[14]. The buffered coastal edges could help to form and locate soft barriers to coastal flooding.

The net effect of these remediation techniques on the catchment can be measured through a recalculation of the permeable/impermeable surface ratio. The consequences are the development of an urban green infrastructure that is more open and greener with several remediatory regimes to help build urban resilience to the effects of climate change.

The implication of this new urban green infrastructure on the conventional real estate programme requires a change in thinking about how the required amount of GFA to make the project financially viable might be allocated.This can be accomplished through the LIUDD strategies of clustering the building programme.By recalculating the GFA into a new FAR, a reconfigured building footprint driven by the dictates of the environmental remediation programme, the financial returns of the original real estate investment can be accomplished. The urban and architectural consequences of the reconfigured urban programs can be modeled in ArcGIS, graphically represented through the extrusion of the proposed building footprint.

2 Case Study

To demonstrate how the development of a new urban green infrastructure could work, a proposed greenfield development study in New Zealand will be discussed. This is a proposal for a new urban development to be located at Whenuapai, Auckland, New Zealand. The study demonstrates the applicability of the three-stage urban green infrastructure design process in dealing with the environmental problems that climate change will have on city. The study demonstrates the way in which these problems can be ameliorated through a three-stage design process.

The case study begins with the identification of what environmental problems are likely to be engendered by the new urban development.Through a study of the catchment at two scales,the main environmental problems are identified as an increase in flooding and the production and entry of contaminated stormwater into the existing hydrological system and thence into the receiving environment.

The second stage of the process is identified the development zones and the environmental implication that the development will have on the catchment. The Rational Method[12]was used as a technique to understand the impact that the ratio of impervious to pervious surfaces within the catchment, before and after the development,would have on the production of stormwater and flooding. The second technique was to protect the existing hydrological network from the entry of contaminated stormwater and flooding. The specific technique was to buffer the existing stream systems. This operation was carried out using GIS mapping and analysis to identify the existing hydrological network, the streams and overland flow paths, then, using the buffering function in ArcGIS, make protection zones around each OLFP and stream[15]. The effect of this operation was to also increase the amount of pervious surface.

The third technique was to cluster the urban form. By acknowledging and buffering the existing hydrological system, the loss of development GFA was inevitable. Clustering the development GFA into a new urban form was a way of ensuring that the projected real estate programme didn’t make for a financial loss[16]. The result for the urban design of the Whenuapai case study was to assemble the “missing”GFA into apartment blocks at the intersection of the stream system with the littoral.

2.1 Whenuapai

Whenuapai is a new urban district planned to the west of Auckland, New Zealand (Fig. 1).Whenuapai is located on the southern side of the upper Waitamata Harbour, with Brigham’s Creek forming a boundary to the west and State Highways 16 and 18 forming the southern and eastern edges of the site. The greater part of the site is a moderately flat plateau approximately 25 m above sea level. An airfield, the Whenuapai Aerodrome,dominates this plateau.

2.1.1 Whenuapai Site Analysis

1)Hydrology. Whenuapai can be divided into eight major catchments (Fig. 2-1). These catchments are eight a number of streams: the Brigham,Rarawara and Waiarohei Creeks. Ten watercourses discharge into the harbour. The average annual rainfall in Whenuapai is 1,333.5 mm, and the average monthly rainfall is 111.1 mm. The average rainfall in January, the driest month, is 79.3 mm.The wettest month is June, with an average rainfall of 147.8 mm.

2)Aspect/Slope. The aspect of Whenuapai is mostly northerly with an east-west division along the sides of the stream corridors (Fig. 2-2).The slope of the majority of the site is flat (0 to 5 degrees); however, alongside some of the stream corridors, the slope increases from 5 to 16 degrees(Fig. 2-3).

3)Vegetation. The site was originally clad in New Zealand’s native coastal forest. The typical vegetation of the coastal edge of the Whenuapai catchment is characterised as belonging to the Kowhai-Kotare Harbour Coastline Ecosystem[17].The dominant tree species areMetrosideros excelsa,Sophora microphylla,Dysoxylum spectabile,Vitex lucens,Agathis australis,Corynocarpus laevigatusandAlectryon excelsus. Shrub species includePittosporum crassifolium,Astelia chathamica,Pittosporum tenuifolium, andMyoporum laetum.

2.1.2 Whenuapai Structure Plan

Auckland is undergoing rapid urban growth.More than 1,000,000 new citizens are expected to arrive in Auckland over the next 20 years.As a consequence of this growth, there is an acute housing shortage. Whenuapai is located adjacent to SH16, an important motorway in the western growth corridor and near the new NorthWest Shopping Centre. Whenuapai also neighbors the successful Hobsonville housing development, making Whenuapai the next site for future urban development. To address the urban pressure Auckland is facing, the Auckland Council developed an urban structure plan for Whenuapai to help conceptualize the shape of future urban development[18]. The structure plan efficiently zones the available land according to proximity to infrastructure; industrial land and an apartment zone located adjacent to the main transport routes,SH16 and 18. Lower density housing zones are located nearer to the edge of the Waitemat Harbour. Single-storey housing with large sites is zoned for the coastal margin, while more intensive housing (medium density) is zoned between the coastal edge and the industrial zone (Fig. 3).

The proposed structure plan will cause a number of environmental problems including an increase in stormwater contamination and flooding;these conditions will be heightened by the effects of climate change. To explore the impact of these effects, a sub-catchment of the larger Whenuapai catchment was chosen as a case study site. The selected site was the Rarawara sub-catchment to both understand the consequences of the proposed urban development and develop strategies to remediate the impact on the environment.

2.2 Rarawara Sub-catchment

2.2.1 Step One: Rarawara Sub-catchment Inventory

The 324 ha Rarawara catchment located in the north of the Whenuapai catchment (Fig. 4). It is a moderately flat site bounded to the north by the Waitemat Harbour. To the west, the site is defined by the Brigham Creek/Pitoitoi stream catchment, to the east by Whenuapai village and airfield, and to the south, by the intersection of SH16 and 18 (Fig. 5).

1)Vegetation. The predominant vegetation in the catchment is grass, the result of the rural economy of the catchment. The other vegetation types are decorative gardens around the housing areas and shelterbelt species from the small horticulture and orchard blocks.

2)Hydrology. The catchment drains into the dominant stream, the Rarawara Creek. The creek runs roughly north-south and bisects the catchment. There are three sub-catchments.The stream exits into an estuarine mouth before connecting to Waitemat Harbour. There are smaller streams from the hinterland to the coast on either side of the Rarawara catchment (Fig. 6).

3)Aspect/Slope. The aspect of the Rarawara catchment is mostly northerly with an east-west division along the sides of the stream corridors (Fig.7-1). The slope of the majority of the site is flat, 0 to 5 degrees, especially the aerodrome site (Fig.7-2).However, alongside the stream corridors, the slope increases from 5 to 16 degrees.

4)Land Use. The land of the catchment is separated into two uses. The first is suburban housing, large lifestyle houses and sections on the northern coastal edge and a smaller subdivision to the west of the airfield. The rest of the catchment is made up of rural lifestyle blocks and small horticulture and orchard blocks.

5)Pervious/Impervious Ratio. Due to its mostly rural nature, the catchment is largely made of pervious surfaces (Fig.7-3). The impervious areas are the roading infrastructure and the airfield(Fig.7-3). The existing Rarawara catchment area is 324.175,3 hm2. The impervious surface area is made up of roads (81.842,8 hm2) and buildings(20.100,4 hm2). The total impervious surface area is 101.943,2 hm2. The total pervious surface area is 220.026,5 hm2. Giving a ratio of pervious to impervious of 2∶1.

2.2.2 Step Two: Rarawara Sub-catchment Development

1)Rarawara Structure Plan. The effect of the Auckland Council’s Whenuapai structure plan on the Rarawara catchment is to configure the catchment into four housing zones and an industrial zone. The area closest to the coast is zoned for low-density,single-storey housing, along an approximately 100 hm2coastal margin. Allowing for one dwelling unit (DU) per 500 m2gives 2,008 DUs, and 50 hm2of impervious surfaces. A medium-density housing zone of 82 hm2is planned behind the coastal zone.Allowing for one DU per 300 m2equals 2,743 DU,giving 61 hm2of impervious surface. The remaining area is zoned industrial/commercial with two apartment zones to the east of the airfield zone.Three parks are proposed of approximately 35 hm2in total. Roads and proposed and existing housing make up 212 hm2of impervious surface (Fig. 8).

2)Rarawara Catchment: Environmental Problems. With the construction of the new housing and the associated infrastructure, the hydrological pattern of the existing territory will be irrevocably changed; increased runoff with increased sedimentation will add to already high levels of sedimentation in the upper Waitemat Harbour. Runoff will also be polluted from roading contaminants and roof debris.

In the Auckland Council structure plan the impervious surface in the Rarawara catchment will increase markedly. The existing Rarawara catchment area is 324.175,3 hm2. The impervious surface area is made up of roads (81.842,8 hm2), and buildings(206.909,5 hm2). The total impervious surface area is 288.752,3 hm2. The total pervious surface area is 35.423,0 hm2. Giving a ratio of pervious to impervious of 1∶8.

If this plan were built, then the result of this high degree of imperviousness would be a large amount of contaminated stormwater runoff discharging into the harbour. And an increase in flooding.

To calculate the volume of stormwater that would be discharged from the catchment under the new structure plan, the Rational Method can be used[12](To calculate the required volume for the construction of a storage and treatment wetland, TP10[19]is used). The runoff discharge flow rate over two years (m3/s) would be 5.95 m3/s.The required storage and treatment wetland for this runoff is sized at 32,140.04 m3. For a tenyear runoff discharge flow rate of 8.71 m3/s, the required storage volume is 47,019.68 m3. For a 100-year runoff discharge flow rate of 13.95 m3/s, the required storage volume is 75,350.53 m3.

3)Rarawara Sub-catchment Environmental Remediation. To ameliorate the effects of urbanization on the coastal receiving environment,an understanding of the hydrological behavior of the catchment is necessary. The first step is to determine the structure and shape and size of the catchment on the site through mapping with ArcGIS. This data can be manifested as a series of maps showing catchment boundaries and a network of overland flow paths. From this mapping, the size of the catchment and the ratio of impervious to pervious surface can be determined. Using the Rational Method, an understanding of the amount of increased rainfall runoff with the expanded site can be gained. By measuring the increase in impervious surface due to the number and type of housing zones, the increase in stormwater runoff can be calculated. Once the connection of housing density to the impervious/pervious surface ratio is established, the different zoning densities and associated impervious/pervious ratios can be manipulated to allow for greater permeability, while at the same time ensuring that the planned number of dwelling units remains the same.

2.2.3 Step Three: Rarawara Sub-catchment Resilience

The environmental damage from an increase in stormwater discharge into the upper Waitemat catchment can be ameliorated through decreasing the amount of impervious surfaces. The removal of infrastructures such as roads and housing will lead to an increase in the amount of pervious surface, leading to an increase in the absorption of stormwater runoff.

1) Landscape. One way to increase the pervious surface of the catchment is by protecting and enhancing the existing stream network by establishing a protective buffer zone of at least 25 m around the stream and overland flow paths(Fig. 9-1). Protection of the coastal edge is another important environmental measure; a buffer of 30 m would give a zone of 43 hm2(Fig. 9-1). These two measures increase the area of pervious surfaces within the catchment by 128 hm2. This intervention also has the effect of developing a new park system along the stream corridors and the waterfront coastal edge (Fig. 9-2).

Accommodating these two measures necessitates a change in the housing footprint. This is accomplished by decreasing the low-density zone from 100 hm2to 23 hm2, and decreasing the mediumdensity zone slightly, from 82 hm2to 74 hm2.

2) Rarawara Catchment: Urban Design. To accomplish the increase in pervious surfaces and the consequent decrease in stormwater discharge means a loss of housing units. Under the Auckland Council structure plan, the number of low-density DUs in the catchment is 2008 and medium density is 2,743, equaling 4,752 DUs (with no provision for high-density units). By enlarging the pervious surface area, the number of DUs in the low-density zone will drop to 473 DUs and in the medium density zone to 2,471 DUs. The shortfall in DUs will be 1,827.

One solution to this real estate shortfall is to substitute apartments for the missing lower density DUs.

This solution will increase the number of DUs to 1,468, making a total of 4,420. By increasing the number of apartments by making the building denser or higher, the shortfall of 1,827 DUs could be matched or even surpassed to give a better real estate return (Fig. 10).

The new apartments could be located in the coastal zone around the existing stream mouth; an area of 8.8 hm2would provide two high-density apartment zones within the low-density area. See perspective (Fig. 11).

Pervious/impervious ratio: The Rarawara catchment area (324.175,3 hm2). Impervious surface of 196.164,2 hm2, roads (65.928,9 hm2)and buildings (130.235,3 hm2). Pervious surface,128.001 hm2. Giving a ratio of pervious to impervious of 2∶3.

3) Rarawara Catchment Runoff. Using the Rational Method, the effect of the new pervious surfaces will lead to a two-year runoff discharge flow rate of 29,304.150,42 m3, compared to the discharge of 26,468.264,89 m3from the original site and 32,140.035,94 m3discharge with the proposed Auckland Council structure plan.

In the ten-year runoff discharge, the flow rate of the new plan is 42,870.886,72 m3, compared to the discharge of 38,722.091,23 m3from the original site and 47,019.682,21 m3from the proposed Auckland Council plan.

In the 100-year runoff discharge, the flow rate of the new plan is 68,701.952,65 m3,compared to 62,053.376,59 m3in the original site and 75,350.528,71 m3in the Auckland Council proposed plan (Tab. 1).

2.3 Implication of the New Green Infrastructure Urban Design Process

2.3.1 Environmental Implications of the Design Process

1) Stream Network. A buffer zone around the revealed hydrological network will enable the stream corridors to be revegetated with native species. The zone also gives the opportunity to allow for the location of structural stormwater cleaning instruments — in particular, wetlands and a rain garden — which can all be installed within the new zone. This stream zone can form a deep connection from the coastal edge to the hinterland,creating an ecological corridor.

Having housing adjacent to the new river zone will also help to increase real estate values. By locating medium-density housing along the edges of the new stream parks, owners can enjoy views of the water and native vegetation. The nature of the new river zones and the link from the coast to the hinterland provide the opportunity for owners in the centre of the development to have access to the coast.

2) Coastal Zone. Establishing a coastal buffer zone means that the critical environmental conditions in this zone will be protected. Critical riparian ecologies can be restored and protected, and damage from the effects of sea level rise in this zone can be ameliorated.

2.3.2 Urban Design

Establishing a protective buffer zone around the coastal and stream hydrological networks will increase the ability of the Rarawara catchment to absorb rainfall, rather than add to runoff into the upper Waitemat Harbour and to slow and dimmish flooding. To ensure the same economic return is met — that the same number of DUs is constructed as specified in the Auckland Council structure plan — the loss of low- and mediumdensity housing is met by a greater number of apartments with a smaller footprint. The result will be a low-rise domestic landscape of gardens and houses broken by apartment towers that emphasise the unique stream system.2.3.3 Whenuapai Catchment: Environmental Implications of the Rarawara Case Study

The new urban green infrastructure plan (Fig.10) shows how the coastline and stream corridors are protected through buffering. There are three consequences of this action. The first is that the vegetative buffers have the effect of protecting the hydrological network by protecting the streams from the influx of contaminated stormwater and flooding. The second effect is that the ratio of impervious to pervious surface is relaxed,ensuring that more rainfall is able to be absorbed by the uncovered ground. A social consequence of this new green infrastructure network is the establishment of a new path/park system that links the hinterland of the subdivision with the coast. The third consequence of this action is the clustering of the GFA that has been displaced by the new stream/buffer stream network into a series of apartment towers located at the intersection of the stream networks and the coast. All these measures will help build future resilience as the environmental effects of climate change become more and more persistent.

3 Conclusion

Climate change will have a devastating impact on our urban environment. Before the knowledge of the transformative power of climate change was fully known, green infrastructure was successfully articulated as a practice in which conventional infrastructural systems could substituted by hybridised ecological structures. This paper argues that the next step in the development of the concept of green infrastructure is to think about the design of the city as a supra green infrastructure. That is,the city itself is embedded in a larger ecological system. To move to this conceptual position which specifically addresses the impact of climate change, involves the use of several readily available techniques, catchment planning, GIS mapping, and standard hydrological calculations.The consequences of these operations are to develop a new urban green infrastructure design process, in which the subsequent city form is more open, greener, and recognises existing hydrological systems. We suggest that the potential for rethinking the city as a green infrastructure is both a safer and more resilient city and at the same time a city with an increased social realm.

This paper examined the limitations of the conventional green infrastructure approach to climate change adaptation. The concept of green infrastructural urbanism presented in the paper explored a new concept of GI. This idea has the potential to exploit the full capacity of GI: not only to form a green network that absorbs more stormwater, but to establish a supra green open structure for a new urban form. This approach moves the design of green infrastructure to the forefront of the urban design process, presenting a radical shift from conventional green infrastructure design as remediation measure to that of the post city construction.

The methodology described in this paper is a catchment-based approach, which uses the hydrological catchment as the analytical unit to capture the full hydrological implication of climate change. This urban green infrastructure design process provides an effective tool for designers to identify the environmental issues that are likely to be engendered by a new urban development. Design techniques described here,such as increasing pervious surface, protecting the existing hydrological network, and clustering the building form, offer an easy-to-follow guide for designers who are working on greenfield developments.

Using the urban development of Whenuapai,New Zealand as a case study, the paper showcases how this urban GI design method can help the designer to identify hydrological patterns within the Whenuapai catchment and the Rarawa subcatchment. The design process demonstrated how a green infrastructure network was formed by identifying the hydrological pattern and how the green infrastructure system subsequently reconfigured the urban form. The resulting masterplan prioritized climate change adaptation strategies, without compromise the building programme and real estate return.

As the effects of climate change escalate in the future, the concept of an urban green infrastructure will shed a light on a broader definition of green infrastructure and its potential to address climate related issues. The catchmentbased design process and its associated techniques have great potential to change the way we design new cities, making them resilient to the ongoing consequences of climate change. While the study is located in New Zealand, we believe that the concept of Green Infrastructural urbanism and the catchment-based design approach is very applicable to building resilience to the effects of climate change in cities across China.

Acknowledgments:

We would like to thank Kevin Zhu for editing the GIS maps.

(Editor / WANG Yilan)