基于“策略—反饋”的琶洲中東區(qū)韌性城市設(shè)計

陳碧琳 孫一民 李穎龍

1 研究背景

國內(nèi)外已有大量文獻(xiàn)辨析韌性城市的概念[1]，闡述工程韌性、生態(tài)韌性到社會—生態(tài)韌性的理念演變[2]。目前學(xué)界仍在進(jìn)一步探討城市韌性的分層研究、規(guī)劃策略和評價體系。

在城市韌性分析方法方面，梅爾等[3]將城市系統(tǒng)的演變分解為基于空間要素流動的“多層模型”，研究世界三角洲城市系統(tǒng)的韌性演進(jìn)規(guī)律。第一層為自然基底層，由土壤、水系、生態(tài)綠地等子系統(tǒng)組成；第二層為城市網(wǎng)絡(luò)基礎(chǔ)層，由交通系統(tǒng)、水利市政等子系統(tǒng)組成；第三層為城市占用層，由土地利用、產(chǎn)業(yè)發(fā)展等子系統(tǒng)組成。戴偉等[4]在此基礎(chǔ)上指出外部不確定擾動與內(nèi)部藍(lán)綠基底和城市系統(tǒng)的矛盾引發(fā)了三角洲空間規(guī)劃的焦點(diǎn)問題。

涉及與韌性相關(guān)的“脆弱性”概念時，當(dāng)前對脆弱性與韌性的關(guān)系存在2種意見：1）若脆弱性的定義與對抗災(zāi)害擾動的能力有關(guān)，則脆弱性和韌性是一組存在負(fù)相關(guān)關(guān)系的概念；2）若脆弱性接近風(fēng)險的定義，則脆弱性與韌性相關(guān)程度較低[5]。筆者傾向于第一種意見并在韌性評價中引入脆弱性分析。

自然基底層與城市網(wǎng)絡(luò)基礎(chǔ)層、城市占用層的對立，造就珠三角特有的脆弱性（圖1）。其中，自然脆弱性（海平面上升、降雨量峰值提高、土地沉降等）受到氣候變化的影響，人為脆弱性則體現(xiàn)為城市擴(kuò)張帶來的環(huán)境污染、硬質(zhì)表面增多和藍(lán)綠系統(tǒng)碎化[6]。

在韌性策略方面，研究主要集中于城市與社區(qū)層面。社區(qū)作為城市子系統(tǒng)，是韌性表達(dá)與落實(shí)的載體，各子系統(tǒng)韌性相互作用，造就了城市整體韌性[7]。申佳可等[8]基于此解讀了韌性社區(qū)規(guī)劃設(shè)計的3個維度，即環(huán)境支撐、空間多樣和以人為本。而針對三角洲這一特定區(qū)域，戴偉等提出了基于系統(tǒng)韌性的三角洲空間規(guī)劃方法，即目標(biāo)確定、系統(tǒng)解譯、系統(tǒng)預(yù)測、系統(tǒng)規(guī)劃與系統(tǒng)反饋。

在韌性評價體系方面，城市尺度上，基于韌性城市指標(biāo)體系[9]，Hernantes等[10]建立了一套成熟的城市韌性評價體系，涉及韌性構(gòu)建的領(lǐng)導(dǎo)力和參與者、城市基礎(chǔ)設(shè)施與自然資源、多方合作等層面。社區(qū)尺度上，彭翀等[11]綜述了一系列社區(qū)韌性評估體系，這些體系通常采用分類的方法，對韌性進(jìn)行賦值和換算的定量評估。

2 韌性城市框架的提出

過去的韌性城市研究提供系統(tǒng)韌性的研究方法，分析城市系統(tǒng)的韌性演進(jìn)規(guī)律，從城市、社區(qū)以及三角洲區(qū)域等尺度上提出韌性規(guī)劃設(shè)計框架和評價體系。然而，目前缺乏在珠三角城市組團(tuán)層面（城市組團(tuán)既包含多個城市社區(qū)，又參與構(gòu)成城市整體）、針對城市基礎(chǔ)設(shè)施與環(huán)境的韌性城市設(shè)計機(jī)制研究，包括如何通過韌性策略解決珠三角脆弱性的問題，如何通過設(shè)計實(shí)踐在城市組團(tuán)層面提升城市整體韌性，如何通過定量方法對韌性策略和設(shè)計實(shí)踐進(jìn)行反饋評價。因此，在已有研究的基礎(chǔ)上，筆者立足于珠三角城市組團(tuán)尺度，通過案例分析，試圖建立一套全過程的韌性城市設(shè)計體系。

作為城市組團(tuán)，廣州琶洲中東區(qū)具有珠三角的脆弱性特征，是珠三角韌性演進(jìn)落實(shí)的載體，因此筆者以其為研究對象，建立微觀尺度上的“分析—策略—方案—反饋”韌性城市設(shè)計機(jī)制，對韌性城市系統(tǒng)的整體性、連結(jié)性、多樣性、冗余性和靈活性[12]等屬性進(jìn)行評價。1）聚焦城市自然基底層和網(wǎng)絡(luò)基礎(chǔ)層，針對城市基礎(chǔ)設(shè)施與環(huán)境，通過災(zāi)害模擬指出低洼的地形、洪澇災(zāi)害的干擾與破碎的城市空間共同導(dǎo)致了琶洲中東區(qū)的脆弱性；2）提出琶洲中東區(qū)3個層次的韌性設(shè)計策略，包括結(jié)構(gòu)性策略、連接方式和節(jié)點(diǎn)處理；3）對應(yīng)上述策略闡述琶洲中東區(qū)城市設(shè)計方案，包括通過強(qiáng)化藍(lán)綠系統(tǒng)和綠色基礎(chǔ)設(shè)施來整合城市各個功能區(qū)，增強(qiáng)濱水區(qū)的步行可達(dá)性，塑造分散式雨水存儲系統(tǒng)和多用堤岸模式；4）利用GIS、Fragstats和Depthmap等軟件，分別對琶洲中東區(qū)場地現(xiàn)狀、原控規(guī)和方案設(shè)計3個樣本進(jìn)行景觀連接度、空間集成度和雨水存儲量的數(shù)據(jù)對比分析，以此評估該韌性策略是否為琶洲中東區(qū)提供環(huán)境支撐，塑造多樣化、以人為本的城市空間。從微觀層面試圖構(gòu)建“分析—策略—方案—反饋”的韌性城市設(shè)計框架（圖2），以點(diǎn)帶面，為珠三角城市的韌性研究和設(shè)計實(shí)踐提供參考。

3 適應(yīng)氣候變化的琶洲中東區(qū)脆弱性分析及韌性城市設(shè)計策略

SCUT-UC Berkeley工作坊首先通過洪澇災(zāi)害情景模擬，探討琶洲中東區(qū)的脆弱性問題，針對這些問題提出3個層次設(shè)計策略：1）結(jié)構(gòu)性策略：連接現(xiàn)有破碎的藍(lán)綠系統(tǒng)；2）連接方式：構(gòu)建基于公共交通為導(dǎo)向（TODs）、垂直水岸的濱水步行可達(dá)空間；3）節(jié)點(diǎn)處理：分散式雨水存儲系統(tǒng)與多用堤岸模式。

3.1 琶洲島脆弱性分析

琶洲島的脆弱性體現(xiàn)在2方面：1）低洼地形（圖3）和海平面上升引起的應(yīng)對洪澇災(zāi)害的脆弱性；2）破碎化的城市空間導(dǎo)致其應(yīng)對氣候干擾的能力隨城市的擴(kuò)張而變?nèi)酢?/p>

琶洲島四面環(huán)水，珠江多年平均最高潮位為8.227 m（廣州高程，珠基高程3.227 m），高于現(xiàn)狀堤頂高程，由于過度依賴堤壩、水閘等剛性手段，面對洪澇災(zāi)害的適應(yīng)能力較弱。脆弱性分析運(yùn)用情景模擬的手法建立琶洲島不同程度雨洪災(zāi)害的預(yù)測模型（圖4），通過模擬發(fā)現(xiàn)臺風(fēng)“山竹”的最高潮位（珠基高程3.227 m）高于200年一遇洪水位（珠基高程2.680 m）①，從側(cè)面說明剛性工程標(biāo)準(zhǔn)不能很好地適應(yīng)洪澇災(zāi)害的干擾。

此外，琶洲島保留了不同時期的村落和工業(yè)區(qū)，其逐漸衰落的基礎(chǔ)設(shè)施不能有效應(yīng)對氣候干擾。場地被多條快速過境交通切割，不同城市空間相互孤立，濱水空間被阻隔，公共交通無法有效覆蓋場地，導(dǎo)致交通和步行可達(dá)性較差。

3.2 琶洲中東區(qū)韌性城市設(shè)計整合策略

3.2.1 結(jié)構(gòu)性策略：連接現(xiàn)有破碎的藍(lán)綠系統(tǒng)

城市空間的破碎化體現(xiàn)在：1）分割與不連續(xù)的空間形態(tài)；2）兼容性差的空間功能；3）阻隔性大的空間聯(lián)系[13]?；谏鐣鷳B(tài)韌性理論，通過建立綠色基礎(chǔ)設(shè)施[14]，為城市提供可浸區(qū)，以下滲、調(diào)蓄、滯流、蒸騰、蒸發(fā)等方式控制城市雨水徑流；同時通過引入休閑娛樂、觀賞學(xué)習(xí)的設(shè)施塑造多用空間，加強(qiáng)人與自然的結(jié)合。因此，琶洲中東區(qū)城市設(shè)計采取連接城市藍(lán)綠系統(tǒng)的措施，整合生態(tài)環(huán)境景觀與高密度城市建成區(qū)，通過韌性設(shè)計提升城市系統(tǒng)的整體性和穩(wěn)固性、多樣性和靈活性、冗余性和連接性來整合空間形態(tài)、豐富空間功能、加強(qiáng)空間聯(lián)系。

1 珠三角城市脆弱性背景分析Background analysis of vulnerabilities of PRD cities

2 “分析—策略—方案—反饋”的韌性城市設(shè)計框架Resilient urban design mechanism of “analysis - strategy - scheme - feedback”

結(jié)合琶洲島地形和水系綠地，方案設(shè)計連接破碎的藍(lán)綠系統(tǒng)，以此為結(jié)構(gòu)骨架設(shè)置可浸區(qū)和防澇片（圖5），縫合水系統(tǒng)和綠地系統(tǒng)，串聯(lián)新舊建成區(qū)。將抬高的堤圍和處于低地的村落進(jìn)行統(tǒng)一設(shè)計，結(jié)合原有河涌和農(nóng)田，建設(shè)城市濕地公園，既可調(diào)蓄雨水，又可供休憩觀賞。

3.2.2 連接方式：構(gòu)建基于TODs、垂直水岸的步行可達(dá)空間

由于緊湊高效的土地利用可支持氣候適應(yīng)性的韌性城市發(fā)展[15]，因此規(guī)劃設(shè)計須考慮在集中建設(shè)區(qū)與生態(tài)底線區(qū)之間以彈性發(fā)展區(qū)作為緩沖[16]，劃定建設(shè)區(qū)邊界，保持城市建成區(qū)和生態(tài)保護(hù)區(qū)的動態(tài)平衡。另外，城市密度與公共交通依賴性密切相關(guān)[17]，因此韌性設(shè)計須通過提升公共交通組織的冗余度來適度提高城市密度。

鑒于此，針對琶洲中東區(qū)重點(diǎn)地段城市空間孤立隔離的問題，方案設(shè)計采用基于TODs、垂直水岸的步行可達(dá)空間聯(lián)系的手法。以公共交通為導(dǎo)向，按500 m步行半徑合理調(diào)整地鐵站點(diǎn)，在站點(diǎn)周邊進(jìn)行緊湊混合的城市開發(fā)，采取“小街區(qū)、密路網(wǎng)”的組織形式，建立多層次的步行連接體系，增強(qiáng)城市與濱水空間的步行可達(dá)性。依據(jù)村落和工業(yè)區(qū)的肌理，方案搭建順應(yīng)水岸形態(tài)的路網(wǎng)結(jié)構(gòu)，增強(qiáng)城市與水的相互滲透。

3.2.3 節(jié)點(diǎn)處理：分散式雨水存儲系統(tǒng)與多用堤岸模式

與現(xiàn)有的集中式防洪排澇工程設(shè)施相比，城市分散式雨水管理景觀基礎(chǔ)設(shè)施采取分散滯流的管理模式，均衡分布于城市內(nèi)部，就近收集雨水，提高雨洪管理能力[18]。

因此，琶洲中東區(qū)重要城市節(jié)點(diǎn)設(shè)計采取更具韌性思維的分散式雨水存儲和多用堤岸模式。設(shè)計探討3種雨洪管理策略（表1），并采取更為靈活的分散式雨水存儲系統(tǒng)，分別通過道路、河道和綠地來存儲雨水（圖6），增強(qiáng)城市韌性。同時方案改進(jìn)了剛性的傳統(tǒng)堤壩模式，將堤岸和保留的工業(yè)區(qū)、村落結(jié)合起來，按空間尺度塑造多用、活躍的堤岸空間。

4 琶洲中東區(qū)韌性城市設(shè)計方案反饋評估

琶洲中東區(qū)韌性城市設(shè)計方案的評估對韌性評價體系的連接性、整體性、冗余性、多樣性和靈活性等指標(biāo)進(jìn)行反饋評價，論證不同層次的韌性策略是否有效提升城市韌性。

其中，針對景觀空間破碎化問題，吳昌廣等開展了景觀連接度研究[19]，Guzy等通過Fragstats的平均歐氏最鄰近距離（ENN_MN）和連接度（CONNECT）參數(shù)研究綠地配置對半水生龜物種豐富度的影響[20]。針對城市空間可達(dá)性問題，利用Depthmap軟件將空間結(jié)構(gòu)轉(zhuǎn)譯成軸線圖進(jìn)行可達(dá)性分析，在蘇州、南京等國內(nèi)城市得到應(yīng)用[21]。

4.1 基于結(jié)構(gòu)性策略的景觀連接度分析

通過GIS（10.5）與Fragstats（4.2）軟件平臺，分別對場地、原控規(guī)和設(shè)計方案的地理數(shù)據(jù)以10 m網(wǎng)格進(jìn)行柵格化處理（圖7），筆者選取類型層次的景觀指數(shù)如斑塊類型面積（CA）、斑塊數(shù)量（NP）、平均斑塊面積分布（AREA_MN）、ENM_MN、斑塊結(jié)合指數(shù)（COHESION）以及500 m步行范圍內(nèi)的連接度進(jìn)行比較。基于上述景觀指數(shù)的比較分析，衡量3個不同樣本的景觀結(jié)構(gòu)特征，對上文提出的結(jié)構(gòu)性策略做出反饋，以調(diào)試連接現(xiàn)有破碎藍(lán)綠系統(tǒng)的手法是否有效增強(qiáng)城市藍(lán)綠系統(tǒng)的景觀連接性、緩解藍(lán)綠空間碎片化的問題。

景觀連接度包含結(jié)構(gòu)與功能連接度，描述了景觀要素在功能和生態(tài)上的有機(jī)聯(lián)系。ENN_MN、COHESION和CONNECT這3個指標(biāo)可用于衡量韌性城市強(qiáng)調(diào)的連接性、整體性和物種多樣性。ENN_MN是指基于斑塊邊緣—邊緣距離所得離斑塊最近的同類型斑塊的距離，用以量化斑塊隔離度；COHESION是指斑塊的整體性或凝聚度，在類型水平上可衡量相應(yīng)斑塊類型的物理連接度；CONNECT是對景觀空間結(jié)構(gòu)單元之間連續(xù)性的量度，反映了同類斑塊在功能和生態(tài)上的有機(jī)聯(lián)系[22]。通過景觀指數(shù)的分析（表2）可知，相比現(xiàn)狀和原控規(guī)方案，設(shè)計方案的水域和綠地類型的ENN_MN值減小，COHESION值和CONNECT值上升，表明在結(jié)構(gòu)性策略引導(dǎo)下，藍(lán)綠斑塊的隔離度下降，而物理和功能上的連接性增強(qiáng)，對加強(qiáng)景觀整體性和緩解生境破碎化具有積極意義。

表1 3種雨洪管理策略比較Tab. 1 Comparison of three stormwater management strategies

表2 基于類型層次上的水域與綠地景觀指數(shù)分析Tab. 2 Analysis of Fragstats metrics of water and green space at type-hierarchy level

表3 路網(wǎng)密度對比Tab. 3 Comparison of road network density

表4 雨水存儲能力部分指標(biāo)比較Tab. 4 Comparison of some indicators of rainwater storage capacity

表5 方案設(shè)計道路儲水計算Tab. 5 Calculation of road rainwater storage in design scheme

4.2 基于連接方式的空間集成度分析

利用Depthmap軟件，分別對原場地、原控規(guī)和設(shè)計方案進(jìn)行空間集成度分析，以衡量構(gòu)建基于TODs、垂直水岸的步行可達(dá)空間設(shè)計是否提升了從城區(qū)到達(dá)濱水空間的便捷程度，實(shí)現(xiàn)韌性評價體系中的交通空間冗余性和城市功能多樣性。

空間句法中，集成度反映系統(tǒng)中某一節(jié)點(diǎn)與其他節(jié)點(diǎn)聯(lián)系的緊密程度，集成度的值越大，表示該節(jié)點(diǎn)在系統(tǒng)中便捷程度越高、公共性越強(qiáng)、可達(dá)性越好。集成度分為整體集成度和局部集成度，整體集成度表示節(jié)點(diǎn)與整個系統(tǒng)所有節(jié)點(diǎn)聯(lián)系的緊密程度，局部集成度表示節(jié)點(diǎn)與附近幾步內(nèi)節(jié)點(diǎn)聯(lián)系的緊密程度，常用3個拓?fù)鋯挝挥嬎?。以整體集成度為X軸、局部集成度為Y軸，建立線性回歸方程，R3即為可理解度?？衫斫舛仍礁叩目臻g，其局部中心性能越能融入全局空間結(jié)構(gòu)之中，從而增強(qiáng)空間系統(tǒng)功能的多樣性與復(fù)雜性[23]。

3 琶洲島高程分析Elevation analysis of Pazhou Island

4 琶洲島洪澇災(zāi)害模擬Flood disaster simulation of Pazhou Island

通過軟件運(yùn)算可得，相比原場地和原控規(guī)，方案設(shè)計的空間集成度更高（圖8），尤其是琶洲中東區(qū)北側(cè)和南側(cè)的濱水可達(dá)性增強(qiáng)，路網(wǎng)密度的提升也加強(qiáng)了交通的冗余性（表3）。另外，通過線性回歸方程的分析（圖9），發(fā)現(xiàn)方案設(shè)計的可理解度（R3）最高，表明該樣本的城市功能更多樣化，有助于實(shí)現(xiàn)在可步行尺度內(nèi)塑造功能混合區(qū)。

4.3 基于節(jié)點(diǎn)處理的雨水存儲量對比分析

根據(jù)分散式雨水存儲的3種方式（道路、河涌和綠地），研究采用如下公式計算原場地、原控規(guī)和方案設(shè)計的雨水存儲總量（Q）的近似值：

式中LR為道路總長度，為道路雨水管截面積平均值，SW為水域總面積，為水域在各地形點(diǎn)可容納水位上升的平均值，SG為綠地總面積，為綠地可下滲的雨水高度。

雨水的存儲總量與LR、SW和SG存在正相關(guān)，筆者以此來比較3個分析樣本的雨水能力（表4）。通過對比可發(fā)現(xiàn)，設(shè)計方案在3個指標(biāo)上均優(yōu)于原場地和原控規(guī)，儲水能力高于二者。

已知SW為19.03 hm3，SG95.23 hm3。參照工程經(jīng)驗，取雨水管截面直徑為1 m，支路、次干道與主干道分別敷設(shè)2、4、8根雨水管，則分別約為1.57、3.14、6.28m3，并依此計算QR（表5）。取河涌可容納水位上升均值為0.1 m，可下滲雨水高度均值為0.2 m，則在方案設(shè)計中，琶洲中東區(qū)重點(diǎn)設(shè)計范圍可儲存雨水總量約為31.4萬 m3。臺風(fēng)“山竹”廣州平均降雨量為76.2 mm②，重點(diǎn)設(shè)計范圍面積為354 hm2，則須容納降雨量約27萬 m3。因此，方案設(shè)計的雨水存儲量高于“山竹”降雨量，增強(qiáng)了琶洲中東區(qū)應(yīng)對洪澇災(zāi)害的韌性。

從上述3項對比評估分析中，上文提出的設(shè)計策略可得到如下反饋：1）連接和整合城市藍(lán)綠系統(tǒng)，提高結(jié)構(gòu)和功能上的景觀連接度，為城市韌性提供了環(huán)境支撐；2）構(gòu)建基于TODs、垂直水岸的步行可達(dá)空間，提升了空間集成度和步行可達(dá)性，塑造多樣化、混合功能、以人為本的城市空間；3）分散式雨水存儲系統(tǒng)能有效靈活地適應(yīng)雨洪災(zāi)害的干擾。

5 總結(jié)

筆者以琶洲中東區(qū)為例，建立了一套“分析—策略—方案—反饋”韌性城市設(shè)計機(jī)制，通過重構(gòu)城市與水系統(tǒng)的和諧共生，促進(jìn)珠三角城市在氣候災(zāi)害中持續(xù)不斷地適應(yīng)和學(xué)習(xí)，增強(qiáng)城市韌性。

1）筆者從韌性城市和韌性社區(qū)的概念內(nèi)涵、珠三角城市與水的發(fā)展空間對立的背景研究出發(fā)，指出在微觀層面上，韌性城市設(shè)計需要在自然基底層和城市網(wǎng)絡(luò)基礎(chǔ)層構(gòu)建穩(wěn)固、多樣、冗余、整體、靈活、相互連接的環(huán)境和城市基礎(chǔ)設(shè)施。

2）筆者以琶洲中東區(qū)為研究對象，分析其因自然與人為因素引起的脆弱性，即低洼地形與洪澇沖擊的矛盾、城區(qū)與水的割裂。然后，對應(yīng)琶洲中東區(qū)的脆弱性，提出3個層次的韌性城市設(shè)計整合策略：提出結(jié)構(gòu)性策略，連接現(xiàn)有的藍(lán)綠系統(tǒng)，整合城市各功能空間；關(guān)注城與水的連接方式，即構(gòu)建基于TODs、垂直水岸的步行可達(dá)空間；對場地的節(jié)點(diǎn)處理，改進(jìn)傳統(tǒng)剛性的工程手段，采取更為靈活的分散式雨水存儲系統(tǒng)。

3）基于原場地、原控規(guī)和韌性城市設(shè)計方案，筆者運(yùn)用各類軟件平臺和數(shù)據(jù)對比分析，針對上述不同層次的韌性設(shè)計策略進(jìn)行反饋評估。結(jié)果表明，相較易受洪澇沖擊的場地現(xiàn)狀，以及對韌性和人本社區(qū)考慮欠缺的原控規(guī)方案，韌性城市設(shè)計方案在微觀層面上能更好地落實(shí)珠三角的城市韌性。

總體來說，這套基于“策略—反饋”的琶洲中東區(qū)韌性城市設(shè)計機(jī)制根據(jù)韌性理論提出設(shè)計策略，運(yùn)用定量分析的反饋評估手段，為微觀層面上珠三角城市組團(tuán)的韌性構(gòu)建提供了參考。不過，由于珠三角城市存在復(fù)雜多樣的脆弱性，對應(yīng)的韌性設(shè)計策略還需進(jìn)行補(bǔ)充，而針對設(shè)計策略的定量反饋方法也有待實(shí)踐檢驗和拓展補(bǔ)充。

注釋：

① 水文數(shù)據(jù)來源：廣州市水務(wù)局。

② 數(shù)據(jù)來源：廣州市政府網(wǎng)站（http://www.gz.gov.cn/gzgov/s2342/201809/4e256dab22ce406ea3bd2b952720 eb64.shtml）。

圖表來源：

圖1～2、4～5、7～9為作者自繪；圖3、6來自SCUT-UC Berkeley工作坊成果；表1～4為作者繪制；表5為作者根據(jù)SCUT-UC Berkeley工作坊成果繪制。

1 Research Background

A large number of literatures at home and abroad have analyzed the definitions of resilient city,explaining the evolution of urban resilience from engineering, ecological to social-ecological resilience.At present, the academia is still further exploring the layer approach, planning strategies and evaluation system of urban resilience.

Meyer et al. put forward a “framework model”with the “l(fā)ayer approach” by decomposing different subsystems, and applied it to study the resilience evolution of world delta cities. The first layer is the natural substratum, the second one refers to the infrastructure networks, and the third one involves urban and agricultural land-use patterns. Dai et al.,based on the model, further pointed out that it is the external uncertain disturbances and the contradiction between the internal blue-green substratum and urban system that trigger the major problem of spatial planning of delta regions.

The authors introduce vulnerability analysis into the resilience evaluation. The opposition of the layers of natural substratum, the infrastructure networks and land-use patterns has caused the unique Pearl River Delta vulnerabilities (Fig. 1). Among them, natural vulnerabilities are mainly affected by climate change,while human vulnerabilities are primarily caused by environmental pollution, increasing hard surface and fragmentation of blue-green system.

The resilience strategies researches have focused on 2 levels-city and community. As an urban subsystem, the community is the carrier of resilience expression and implementation. Shen et al. further interpreted 3 dimensions of resilient community planning and design, namely environmental support,spatial diversity and human-oriented concept.

As for resilience evaluation system, on macro-scale of a city, based on the city resilience framework, Hernantes et al. developed a proven evaluation system in the construction of resilience. On micro-scale of communities, Peng et al. reviewed a series of community resilience assessment systems, which generally adopted the method of classification to quantitatively evaluate resilience by assignment and conversion.

2 Proposal of Resilient Urban Design Mechanism

According to the background research,the previous studies on resilient city provided research methods of system resilience, analyzed the resilience evolution of urban systems, and proposed resilience planning framework of cities,communities and delta region. However, there lacks researches in Pearl River Delta on resilient urban design mechanism for urban infrastructure and environment in the micro-level urban groups, which include how to solve the vulnerability problems through resilience strategies, how to implement urban resilience through design practices of urban groups, and how to evaluate resilience strategies through quantitative methods. Therefore, based on the existing researches, the authors focus on the specific micro-scale city groups of Pearl River Delta, and try to establish a whole-process resilient urban design framework through case study.

As a micro-level city group, central and eastern Pazhou, which processes the typical vulnerability characteristics of Pearl River Delta,is the carrier to implement urban resilience. The authors take it as the showcase and propose a resilient urban design mechanism of “analysisstrategy-scheme-feedback” (Fig. 2) at the microlevel, and evaluate the attributes such as integrity,connectivity, diversity, redundancy and flexibility of the resilient urban system: focusing on the layers of natural substratum and the infrastructure networks, the vulnerabilities of central and eastern Pazhou are caused by low-lying terrain, interference of floods, and fragmented urban space through disaster simulation; 3 levels of resilient urban design strategies are proposed, including structural strategy,connecting methods and urban nodes design measures; the urban design scheme is demonstrated,with integrating urban spaces through strengthening the blue-green system, enhancing the accessibility of the waterfront area, and adopting distributed rainwater storage system; based on GIS, Fragstats and Depthmap software, the data of landscape connectivity, spatial integration and rainwater storage are analyzed for current site, original plan,and design scheme, to assess whether the resilience strategies provides environmental support for the climate change, and whether it will shape a diverse,human-oriented urban space.

3 Vulnerability Analysis and Resilient Urban Design Strategies of Central and Eastern Pazhou Adaptive to Climate Change

3.1 Vulnerability Analysis of Pazhou Island

Vulnerabilities of Pazhou Island are reflected in the following: the low-lying terrain (Fig. 3),causes the vulnerability of floods, the fragmented urban space makes this island an isolated area and difficult to respond to climatic disturbances.

Pazhou Island is surrounded by water, and the average highest tidal level of Pearl River is 8.227 m(Guangzhou elevation), which is higher than the current elevation of the embankment (8.05 m). The disaster scenario simulation is employed in vulnerability analysis to establish a predictive model for different degrees of floods in Pazhou Island (Fig. 4). Through simulation,it is found that the highest tidal level of Typhoon Mangosteen (3.227 m of Pearl base elevation) is higher than the 200-years flood level (2.680 m)①,causing backflow of Pearl River, which demonstrates that the rigid engineering means may not adapt well to the floods and waterlogging.

In addition, the declining infrastructure and poor pedestrian accessibility of villages and industrial districts in Pazhou can not effectively cope with climate interference.

3.2 Integral Resilient Urban Design Strategies of Central and Eastern Pazhou

3.2.1 Structural Strategy: Relinking the Existing Broken Blue-Green System

The fragmentation of urban space is embodied in 3 aspects: the spatial form of segmentation;the spatial function with poor compatibility; the spatial connection with strong barriers. Based on social-ecological resilience, green infrastructure can provide city with floodable areas by controlling urban stormwater runoff. Meanwhile, by introducing recreational facilities, green infrastructure strengthens the interaction between human and nature. By integrating ecological environment and high-dense urban built-up area, green infrastructure enhance the integrity and stability, diversity and flexibility,redundancy and connectivity to respectively integrate spatial form, enrich spatial function, and strengthen spatial connection.

According to the existing topography, water system and green space of Pazhou Island, the design scheme reconnects the blue-green system,and utilizes it as the structural framework to arrange the floodable areas and anti-waterlogging spaces (Fig. 5), to suture the blue-green system and to connect historic and new districts.

3.2.2 Connecting Strategy: Creating Walkable Urban Space Based on Transit-Oriented Development and Vertical Waterfront

Compact and efficient land use pattern could underpin climate resilient urban development.Therefore, planners are well-advised to consider the elastic development zone standing as a buffer between the centralized constructed areas and ecological protected districts, to maintain the dynamic balance between built-up area and the ecological region. Besides, because of the high relevance between urban density and public transport, the resilience design enhances the traffic redundancy to moderately increase urban density.

In view of the isolation of city space, the design creates walkable urban space based on transitoriented development and vertical waterfront. With metro stations adjusting in 500-meter walking radius,the design adopts the “small blocks and dense road network” pattern to establish a multi-level pedestrian connection system and enhance walkability between city and water.

3.2.3 Node Design Strategy: Distributed Rainwater Storage System and Multi-functional Embankments

Compared with the existing centralized flood control, decentralized rainwater management,adopts a distributed and stagnation mode, which is evenly distributed within the city to collect rainwater directly.

6 分散式雨水存儲模式Distributed rainwater storage mode

7 3個分析樣本柵格化圖像Raster images of three analyzing samples

8 空間集成度分析Analysis of spatial integration

Therefore, node design of central and eastern Pazhou prefers the resilient distributed mode and multi-functional embankments. The scheme explores 3 stormwater management strategies(Tab. 1) and adopts a more flexible decentralized stormwater storage system through roads, rivers and green spaces (Fig. 6).

4 Feedback Assessment of Resilient Urban Design of Central and Eastern Pazhou

4.1 Analysis of Landscape Connectivity Based on Structural Strategy

Based on GIS and Fragstats, the geographic data of current site, original plan and design scheme are rasterized by 10 m grids (Fig. 7).The class-level metrics are selected, such as CA,NP, AREA_MN, ENN_MN, COHESION and CONNECT within a 500 m-walking range. Based on the comparative analysis of the above metrics,this research measures the landscape structural characteristics of 3 samples, and provides feedbacks on the above-proposed structural strategies to debug whether relinking the broken blue-green system enhance the landscape connectivity and mitigate the fragmentation problem.

Landscape connectivity includes structural and functional connectivity, describing the organic relationship between landscape elements in function and ecology. The three metrics,ENN_MN, COHESION and CONNECT, can be used to measure connectivity, integrity and species richness which resilient city emphasizes.Among them, ENN_MN is a measurement of patch isolation, by using Euclidean geometry as the mean shortest straight-line distance between the focal patch and its nearest neighbor of the same class; COHESION means the cohesion or integrality that is a measurement to quantify the physical connectivity; CONNECT is a measurement to quantify the continuity of the space structure units, which reflects the organic connection between the function and ecology of the patches. According to the data analysis of the fragstats metrics (Tab. 2), compared with the site and the plan, the ENN_MN value of water system and green land of design scheme is reduced, while the corresponding value of COHESION and CONNECT are increased, indicating that with the guidance of structural strategy, the isolation of blue and green patches is declining, while the physical and functional connectivity is enhanced.

4.2 Analysis of Spatial Integration Based on Connecting Strategy

Based on Depthmap software, the research respectively analyzes the spatial integration of current site, plan and design scheme, to measure whether the walkable spatial design based on transit-oriented development and vertical waterfront improve the convenience between city and water, and whether it can realize the traffic redundancy and the functional diversity.

The integration value reflects the closeness of connection between one node and others in a system. The greater value of the integration would make the convenience higher, the publicity stronger and the accessibility of the node in that system better. Spatial integration can be divided into integral and partial integration. The integral value indicates the closeness of the connection between a node and all nodes in the whole system,while the partial one value indicates the closeness of the connection between a node and the nodes in nearby topological steps. The linear regression equation is established with the integral integration asX-axis and the partial integration asY-axis,and the correlation coefficientR2 is marked as intelligibility. The higher the intelligibility value is, the better the space can be integrated into the global spatial structure, thus strengthening diversity and complexity of spatial functions.

9 集成度散點(diǎn)圖及線性回歸方程Scatter plots and linear regression equation of spatial integration

It can be obtained through calculations that the integration value of scheme design is higher than that of site and plan (Fig. 8), and the upgrade in road network density also reinforces the traffic redundancy (Tab. 3). Besides, the intelligibility (R2)of the scheme is the highest (Fig. 9), illustrating that urban function of this sample is more diversified.

4.3 Comparative Analysis of Rainwater Storage Based on Node Design Strategy

According to 3 ways of distributed rainwater storage (roads, rivers and green land), the following formula is used to calculate the approximate value of the total rainwater storage (Q) of current site,original plan and design scheme (LR: total length of road network,: average value of the cross-sectional area of road rainwater pipes,SW: total area of the water,: average value of the water level that can be accommodated of the water points at various locations,SG: total area of green space,rainwater height that can be infiltrated into the green space).

As demonstrated in the above formula, there is a positive correlation between total rainwater storage andLR,SWandSG. The rainwater storage capacity of 3 samples is compared (Tab. 4) and it is found that design scheme is superior to current site and original plan in all the 3 indicators and the rainwater storage capacity is also better.

SWis known to be 19.03 hm2 andSGis 95.23 hm2.Referring to engineering experience, the diameter of the rainwater pipe is about 1m, and 2, 4 and 8 rainwater pipes are laid along main roads, secondary roads and branches, respectively (Tab. 5). And the values ofare 0.1 m and 0.2 m respectively, so in the design scheme, 314,000 m3 of rainwater can be stored in the key design scope. On the other hand, the average rainfall of Typhoon Mangosteen in Guangzhou is about 76.2 mm②with the key design scope of 354 hm2, and central and eastern Pazhou thus needs to contain about 270,000 m3 rainfall, which means rainwater storage of design scheme is higher than the rainfall volume of Mangosteen.

From 3 comparative assessments, the design strategies proposed above can get the feedbacks as follows: connecting and integrating the urban bluegreen system can improve structural and functional landscape connectivity; creating walkable urban space based on transit-oriented development and vertical waterfront can upgrade the spatial integration and pedestrian accessibility; the distributed rainwater storage system can effectively and flexibly adapt to the interference of floods and waterlogging.

5 Summary

With central and eastern Pazhou as the research object, the authors analyze its vulnerability caused by the contradiction between low-lying terrain and floods and the separation of urban and waterfront. And then 3 levels of integral resilient urban design strategies are proposed: the structural strategy is put forward by relinking bluegreen system; the connecting mode of city and water is proposed by creating walkable urban space based on transit-oriented development and vertical waterfront; a more flexible node design is promoted by improving rigid engineering water conservancy and adopting a distributed rainwater storage system.

Various software and data comparison are utilized to evaluate different levels of resilience design strategies based on current site, original plan and resilient urban design scheme. The feedbacks illustrate that the design scheme can better implement urban resilience in Pearl River Delta at the micro-level, compared with current site which is vulnerable to floods and the original plan which lacks consideration of resilient and human-oriented community.

Generally speaking, this “strategy-feedback”resilient urban design mechanism of central and eastern Pazhou proposes design strategies based on resilience theory and utilizes the quantitative assessment method to provide a reference for constructing urban resilience at micro-level in Pearl River Delta city groups, however, due to complex vulnerabilities in Pearl River Delta, the resilience strategies need to be supplemented, and the corresponding quantitative feedback methods are yet to be tested and further expanded.

Notes:

① Source of the above hydrological data: Guangzhou Water Bureau.

② Source: Guangzhou Municipal Government Website(http://www.gz.gov.cn/gzgov/s2342/201809/4e256dab22ce 406ea3bd2b952720eb64.shtml).

Sources of Figures and Tables:

Fig. 1-2, 4-5, 7-9 are made by authors; Fig. 3, 6 are from design document of Workshop SCUT-UC Berkeley; Tab.1-4 are made by authors; Tab. 5 is made according to the research results of Workshop SCUT-UC Berkeley.