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    滨海港口城市长期避难场所布局与灾害危险适应问题探讨
    2019-07-19  点击:[]

    滨海港口城市长期避难场所布局与灾害危险适应问题探讨

    Study on Hazard Adaptation of Long-term Shelters’ Location in Coastal Port Cities

    张威涛 运迎霞

    ZHANG Weitao,YUN Yingxia

     

    张威涛 / 1987 年生 / / 天津人 / 天津大学建筑学院 2013 级博士研究生 / 研究方向 :滨海大城市防灾规划

    通信作者邮箱 (Correspondent author E-mail):zhangwt2015@outlook.com

    ZHANG Weitao, born in 1987, female, was a doctor of grade 2013

    from the School of Architecture of Tianjin University. Research direction: disaster prevention planning of coastal major cities.

     

    运迎霞 / 1957 年生 / / 天津人 / 天津大学建筑学院教授 / 博士生导师 / 研究方向 :城市土地利用规划 生态城市设计

    YUN Yingxia, born in 1957, female, was a professor and doctoral supervisor in the School of Architecture of Tianjin University. Research direction: use and planning of urban land and eco-city design.

    摘要:滨海港口城市中,公园绿地虽然具备地震和火灾避难职能,但无法针对风暴潮起到防御作用,需要和建筑避难所一起,形成地震、风暴潮、火灾避难场所的共同配置。探讨并提出避难场所“规避性适应”灾害危险的空间布局原则,能确保避难场所在承担长期避难生活时为避难者提供场所和环境的双重安全保障。本文对我国某滨海港口城市局部做实证研究,通过 GIS 空间分析软件中的核密度分析与热点分析,分别识别并比照三类长期避难场所和对应的三种灾害危险的空间分布。结果发现,长期风暴潮和火灾避难场所分别可以有效地规避地震和火灾高危险区,但是分布局限且边缘化;地震避难场所不仅可以有效规避地震高危险区,并且分布较广泛。基于此,本文提出了减缓风暴潮和火灾危险、增加长期风暴潮和火灾避难场所分布的具体优化策略。

    关键词:滨海港口城市;长期避难场所;灾害危险;适应性

    Abstract: In coastal port cities, green lands are important shelters responding to earthquake and fire, but not storm tide. Building shelters should be allocated to prevent storm tide. Therefore, three types of shelters are allocated in coastal port cities. Long-term shelters should obey “avoidable adaptation” of hazard. It means shelters' construction structure should be safe and surrounding environment should be away from high hazardous area, meanwhile, shelters' capacity should be redundant. This paper is in a China's case study. Firstly by Kernel Density Tool and Hot Spot Tool in GIS, three long-term shelters' layout and three hazards layout were analyzed. To compare between these two layouts, it is found that long-term storm-tide shelters and fire shelters are located away from the corresponding high hazards, but the location are too narrow and marginal. By contrast, earthquake shelters can adapt to its hazard more efficiently. Based on these outcomes, detailed strategies for reducing hazard and improving shelters' layout are proposed.

    Key words: coastal port cities; long-term shelters; hazard; adaptation


    1 引言

    我国滨海港口城市同时受到地震、风暴潮和火灾的三重灾害威胁:东南沿海地区位于环太平洋断裂带,地震灾害威胁严峻;18 000 km 海岸线几乎全部受到风暴潮的影响[1];港口带动制造业、能源业、仓储物流业等产业园区建设,涉及易燃易爆品的规模化生产、使用和运输,原生自然灾害和人为事故都可能引发工业爆炸起火。面对如此复杂多样的灾害危险,滨海港口城市必须规划建设地震、风暴潮和火灾三类避难场所,即公园绿地与建筑避难所共同配置,确保民众在三类灾害场景下都能获得安全收容。

    避难场所的规划建设是防灾能力构建的重要内容之一。我国学者王江波在城市综合防灾规划编制中的关键问题探讨中,提出“灾害风险与防灾能力的关系,就如同矛与盾的关系。理想的状态下,两者应是正比关系,即灾害的风险性越高,城市的防灾能力应越强[2]。本文提出避难场所对灾害危险的响应主要体现在适应性,即面对自然灾害威胁时,在尊重自然灾害客观规律的前提下,发挥主观能动性[3]。适应性内涵在长期避难场所的规划布局上尤其凸显:其一,长期避难场所要确保民众灾后避难生活时,场所安全和环境安全的双重保障,不仅要强调避难场所场地或建筑结构的灾害防御能力,还要撤出高灾害危险区,规避二次灾害和次生灾害隐患;其二,增加低危险区中长期避难场所容量,确保对高危险区撤出民众的有效收容。

    滨海港口城市中,地震、风暴潮与火灾三类长期避难场所分布是否可以分别“适应”相应的危险,是本文探讨的核心内容。首先,梳理各类避难场所的建设形式,包括公园绿地具备的抗震和防火职能以及建筑避难所具备的抗潮职能。然后,提出长期避难场所布局对灾害危险的“规避性适应”原则。基于此对我国某滨海港口城市局部代表地区展开实证研究,首先采用 GIS 空间分析软件对现有避难场所备选用地分布和灾害危险分布进行可视化,然后通过一一比照,总结现有适应问题,最后提出改进或优化策略。

    2 避难场所类型

    避难场所的建设形式决定了对某一灾种是否具备防御能力(表1)。

     

    1 避难场所建设形式与标准

    Table 1 The Form and Standard of Shelters

     

    避难场所类型

    建设形式与标准

    备选设施或用地

     

     

    长期地震 避难场所

     

     

    长期风暴潮避难场所

     

    附属开敞空间不小于 1hm2 的多层防灾建筑

     

    文化设施、教育设 施、福利设施等

    长期火灾避难场所

    不小于 10hm2 的开敞空间

    公园绿地、体育设施等

     

     

     

     

     

     

     

    注:长期地震避难场所面积标准采用日本广域避难场所面积标准,以具有充分的人口收容和设施配套空间;长期风暴潮避难场所附属开敞空间面积标准参考日本紧急避难场所面积标准,确保人车集散空间。

    Note: In order to have adequate space for population reception and facilities, the long-term earthquake shelter area standard adopts the Japanese wide area shelter standard, and the long-term storm-surge shelter ancillary open space area standard refers to the Japanese emergency shelter area standard to ensure the distribution space of people and vehicles.

     

    对于地震防御而言,公园绿地可以避免建筑设施与地面铺装的损坏、发挥植被的物理减灾效用、容纳大规模机动车与重机设备的出入停放、便于搭建帐篷和设置停机坪等一场多用、发挥植被景观的心理安抚作用等,具有一定规模开敞空间的建筑场所型的地震避难场所还可以提高避难者的长期住宿条件。

    大型公园绿地对于火灾防御具有决定性影响。根据日本从关东大地震与阪神大地震中获得的有关大火火流对防灾公园包围的经验可知[4],只有当开敞空间达到 100 000 m2,内部地区才可以保障安全。另外,大型公园绿地作火灾避难场所时,对于外部起防护隔离的植物配置方式具有更高的要求。目前,日本FPS栽植法被广泛采用(图 1),将公园从外向内分为火灾危险带(F)、防火树林带(P)和活动空间(S)。F区选择树干难以着火、叶片难以立即燃烧的树种;P区植物的选配应当以比F区耐火性更高的树种为主,适当配置乔木和灌木,提高避难区的遮蔽率;S区根据需要种植一般的园林植物[5]。另外,为了强化植被立体配置的防灾效果,并丰富景观层次,还可采用FPS改进模式(图2)。

     

    说明: 图片包含 屏幕截图已生成极高可信度的说明


    1 FPS 模式     2 FPS 改进模式

    (图片来源 :参考文献 [5]   (图片来源 :参考文献 [5]

    Figure 1 FPS model    Figure 2 Improved FPS model

    (Sources References [5]   (Sources References [5])


    然而,公园绿地不具有风暴潮抵御能力,此时避难者必须向高处疏散,所以钢筋混凝土(或加固)结构与具备防震、防浪、防风和公共使用性的公共服务建筑,成为理想的风暴潮避难场所。

    3 长期避难场所布局和灾害危险的规避性适应原则

    广义的灾害危险指灾害风险,包括致灾危险性和承灾体脆弱性两个维度。狭义的灾害危险仅指致灾危险性,由致灾因子与孕灾环境共同作用形成,表现为灾害发生的可能、频率、强度、范围、时长等。本文主要研究狭义的灾害危险。

    “适应”灾害危险是防灾能力的多种表现之一,最关键的内涵是尊重自然灾害客观规律和发挥人类主观能动性之间的权衡。当灾害影响可以避免或影响可控时,“适应”灾害即为“抵御”灾害;当无可避免或影响不可控时,“适应”灾害即为“规避”灾害。

    就民众避难行动而言,“适应”灾害危险就是在高危险区确保紧急庇护,而后当条件允许时,尽快撤离灾害高危险区并向低危险区转移,避免在高危险区的长期滞留。换言之,容纳灾后避难生活的长期避难场所,其布局应该遵守规避性适应灾害危险的原则:第一,长期避难场所主要分布在低危险地区,确保避难生活的场所和环境双重安全;第二,确保长期避难场所的容量具有冗余性,有能力接收由高危险地区转移而来的大批避难者。这两点会使得长期避难场无论从空间分布还是建设规模上,都表现出向低危险区的高度集中。

     

    4 研究方法

    4.1 灾害危险指标与评价

    如表2所示,在地震危险评价中,由于滨海地区土壤盐渍化程度高,土壤液化可能性大,会造成更严重的地面铺装和建筑设施损坏,所以土壤液化应作为除地震烈度之外重要的地震危险评价指标;在风暴潮危险评价中,浸水深度与地势呈正相关,滨水损失则指当河流成为海水涌入内陆的洪水走廊,沿河地区与其他地区相比在同样浸水深度下的水流速度会更高,已有研究表明,沿河1 km 范围内建筑与设施的损毁程度明显更大[6];在火灾危险评价中,虽然危险性生产活动、设备材料集中的港口地区,会因油气泄露和爆炸引发严重火灾,但是高密度种植和大面积的防护林对抑制火势增长、阻挡火灾蔓延具有显著作用。

    采用指标体系评价法[7],分别评价每种灾害危险。首先,以城市主干路为边界划分街块单元[8];然后,按照公式(1)测算各项指标得分,通过数据标准化将得分纳入同一单位尺度;最后,指标等权求和获得各灾种的综合评价值。根据美国学者 Prasad2016)对于假设指标权重相等的适宜性探讨[9],本文假设各评价指标等权重,不仅利于为风暴潮避难场所分布的改进提供较为全面的自然地理和城市建设依据,还便于为相似地区的规划研究提供可复制和易计算的方法借鉴。

    4.2 灾害危险空间分布的识别

    获得各灾种的灾害危险评价结果后,通过 ArcGis10.2 热点分析(Hot Spot Analysis)分别对研究区域中地震危险、风暴潮危险、火灾危险进行空间聚类分析,用以识别高低值之间的分布差异。热点分析的结果中,高值(热点)和低值(冷点)的分布具有统计学的显著意义。以热点为例,其特征是首先评价单元自己是高值,其次它还被其他同样具有高值的评价单元包围。

    4.3 长期避难场所空间分布的识别

    采用 ArcGis10.2 核密度分析(Kernel Density),计算 2000 m 邻域范围中各类备选避难场所的规模(本文采用占地规模)加权密度,获得避难场所的数量与面积在研究区域内的总体分布情况。已有研究表明 2000 m 为应急响应条件下步行最大范围,2000 m 外无法支持有效的步行活动,会使长期避难场所服务能力骤减。所以,2000 m 作为长期避难场所核密度邻域范围的考量具有合理性。

    街块单元内,每种等级的用地面积(Si)占单元总面积(S)的比与该等级值(Li)乘积的和公式(1

     

     

    2 灾害危险评价指标

    Table 2 Indicators for disaster risk evaluation

    评价灾害

    测算公式

    评价指标

    灾害危险性等级描述

     

     

     

    1   地震

     

    Hazard_ 地震

     

     

    1. 地震烈度

    4 : 断裂带 50m 内(4, 震动峰参

    数 0.2g(3),0.15g(2),0.1g(1).

    =ID_ 地震烈度

    2. 土壤液化

    4 : 严重(4, 较严重(3,

    +ID_ 土壤液化

    般严重(2, 可能存在(1.

     

     

     

    2   风暴潮

     

    Hazard_ 风暴潮

     

     

    1. 浸水深度

    4 :3m 以上浸水深(4,2-3m

    3),1-2m(2),0-1m(1).

    =ID_ 浸水深度

    2. 滨水损失

    3 级 : 河道沿线 0-250m(3),   250-

    +ID_ 滨水损失

    500m(2), 500-1000m(1).

     

     

     

    3   火灾

     

    Hazard_ 火灾

     

     

    1. 工业起火

    4 : 工业制造业、物流仓储与危险

    性公用设施用地(4, 缓冲区 0-250m

    =ID_ 工业起火

    2. 防火防爆

    3), 250-500m(2),   500-1000m(1).

    -ID_ 防火防爆

    2 : 防护绿地(2, 公园绿地(1.

    5 实证研究

    5.1 研究区域与数据来源

     

    3 本文研究范围用地分布图

    Figure 3 Land Use Distribution Map in This Thesis

     

    我国某滨海港口城市地处地震活动的重点监视地区,同时也是我国风暴潮最多发的地区之一。该城市集制造、能源、仓储、物流、居住、服务于一体,是我国综合性现代港口城市地区的典型代表。本文主要研究该城市局部代表地区(图3),包括东部港口地区、内河沿岸地区、西北部内陆地区,占地约 410 km2,以城市主干路划分街块单元 292 个。按照表1对现有用地进行提取,其中长期风暴潮避难场所备选用地 185 处;长期火灾避难场所备选用地 97 处;长期地震避难场所备选用地 282 处。

    因为长期地震避难场所备选用地是长期风暴潮避难场所和长期火灾避难场所备选用地的和,所以下面先探讨风暴潮和火灾的适应问题,最后探讨长期地震避难场所的危险适应问题。

    5.2 长期风暴潮避难场所与风暴潮危险分布结果

    备选长期风暴潮避难场所空间分布非常不均匀,在西北内陆非常集中(图 4-1)。虽然中部地区有不少风暴潮避难场所分布,但因建设饱和、用地紧张、地价高昂等原因,公共服务设施占地面积普遍偏小。西北内陆地区则相反,大型教育科研用地成组布局,成为长期风暴潮避难场所核密度高且集中的主要原因。

    风暴潮危险分布也表现出显著的空间分异,滨海沿线和内河入海口地区的危险性最高,这是由于近海地势低,增加了风暴潮的可能浸水深度(图 4-2)。另外,大规模填海造地将城市建设用地向海域延伸,使风暴潮的可能浸水范围变大。内河和港口的狭长码头都构成了风暴潮洪水走廊,会加大沿岸滨水损失。

    5.3 长期火灾避难场所与火灾危险分布结果

    备选长期火灾避难场所主要受区域生态廊道的布局影响,主要在研究范围的西部边缘集中。但是在内部地区,因为建筑密度高而大型公园绿地较少,使得火灾避难场所分布的核密度非常低(图 5-1)。

    火灾危险分布也表现出显著的空间分异,滨海且港口地区灾害危险最高。因为港口地区分布有危化企业,仓储物流用地也存放有大量易燃易爆品,火灾爆炸隐患很大。另外,相较内陆生活聚集区,港口地区工业大型公园绿地建设不足,也使得其缺乏防火防潮功能(图 5-2)。

     

    4-1 长期风暴潮避难场所占

    地规模加权核密度分布

    Figure 4-1 Weighted Kernel Density Distribution of Long-term Storm Surge Shelters

    4-2 风暴潮危险分布

    Figure 4-2 Risk Distribution of Storm Surge

     

    5-1 长期火灾避难场所占

    地规模加权核密度分布

    Figure 5-1 Weighted Kernel Density Distribution of Long-term Fire Shelter Size

     

    5-2 火灾危险分布Figure 5-2 Fire risk distribution

     

    6-1 长期地震避难场所占

    地规模加权核密度分布

    Figure 6-1 weighted kernel density distribution of long-term earthquake shelter size

     

    6-2 地震危险分布

    Figure 6-2 Earthquake risk distribution

     

    5.4 长期地震避难场所与地震危险分布结果

    如前文所示,备选长期地震避难场所是备选长期风暴潮和火灾避难场所的总和,所以其空间分布表现为二者结合的特征——主要集中于西北内陆地区,依靠大型公园绿地、体育用地、教育科研用地共同形成(图 6-1)。地震危险分布表现出显著的空间分异,滨海大范围地区为海相沉积区,土壤盐渍化程度明显偏高,且受地震带交汇影响,地震动峰参数高。总体而言,滨海地区较西北内陆地区表现出更高的地震致灾危险性(图 6-2)。

     

    6 讨论与结论

    第一,对于风暴潮灾害而言,长期避难场所的集中分布可以有效规避高危险区,但其影响范围较局限。长期风暴潮避难场所有三处集中分布,均由教育科研设施构成且都位于低危险区中。但是其服务范围过于集中,没有充分利用更大范围的低危险地区,也可能导致高危险区人口向低危险区转移后无法充分收容。

    为了优化长期风暴潮避难场所布局对风暴潮危险的适应性,可以从减缓风暴潮灾害危险和增加风暴潮避难场所的分布两方面策略入手。其一,在海岸线和内河岸线都设置潮灾防护林,为了提升景观质量、加入公共活动属性,防护林、海绵设施、公园绿地结合布设。其二,低危险区主要位于研究区域的中心外围地区,现阶段仍存在公共服务配套滞后的情况,但也还留有具有较多的城市建设用地资源。应该充分利用低危险区大力补充文化、福利等公共服务配套设施,在保障民生的同时扩大风暴潮避难场所集中分布的影响范围。同时,对于中心地区,由于建设饱和且地价甚高,通过加建或扩建现有公共服务设施来大幅提升风暴潮避难场所密度显得乏力,此时可以将商业服务业设施纳入风暴潮避难场所的指定范围,这就需要政府与商业服务业设施拥有者和管理者签订灾前协定,并通过资金奖励或容积率奖励等方式,鼓励商业服务业的加入。

    第二,对于火灾而言,长期避难场所的主要分布可以规避高危险区,但其影响范围不仅局限,而且边缘化。长期火灾避难场所有两处集中分布,均依托区域贯通的生态廊道形成。其中一处大的集中分布位于低危险区,而另一处小的集中分布位于高危险区。总体而言,集中分布的影响范围过于局限且边缘化,未充分利用更大范围的低危险地区,同时可能导致高危险区人口向低危险区撤离距离过远,且无法有效收容。

    为了优化火灾长期避难场所布局对火灾危险的适应能力,可以从减缓灾害危险和增加火灾避难场所的分布两方面策略入手。其一,在高危险区和低危险区之间增设防火防爆林带[10],可以依托对外交通等高等级道路沿线布置,也应串联大型城市公园,构成兼具生态减灾功能和景观休闲功能的城区绿廊。同时,加大北部产业园区中危险性企业入驻门槛,不允许五级及以上企业(危险品分级方法)和CD类企业(安全生产分级方法)进驻,强化致灾危险管理制度和消防能力。其二,增加内陆西南地区中教育科研用地的开敞空间规模和绿化率,强化用地植物立体化、组团化配置,提高其作为火灾避难场所的能力。

    第三,对于地震灾害而言,长期避难场所的主要分布可以规避高危险区,且其影响范围较广。长期地震避难场所由长期风暴潮避难场所和长期火灾避难场所共同构成,无论从位置还是规模,都表现出较强的地震危险适应性。

    以我国某滨海港口城市局部代表地区为例,揭示现有中长期地震、风暴潮、火灾避难场所备选用地分布存在的灾害危险“适应性”问题,研究结果不仅说明现有各类避难场所备选用地分布还有待进一步完善,还反映出现有城市环境安全有待提升,单独依靠一方的改进无法完全解决“适应性”问题。

     

    1 Introduction

    The triple disasters of earthquake, storm surge and industrial explosion threaten the coastal port cities of our country. Because the southeast coastal area is located in the Pacific Rim fault zone, the threat of earthquake disaster is serious; and almost all the 18 000 km coastline is affected by storm surge [1]; the port drives the construction of industrial parks such as manufacturing, energy industry, warehousing and logistics industry, etc. Involving the large-scale production, use and transport of flammable and explosive materials, primary natural disasters and man-made accidents can lead to industrial explosions and fires. In the face of such complex and diverse disaster risks, coastal port cities must plan and build three types of shelters against earthquakes, storm surges and fires, that is, park green space and building shelters. This ensures that people can be safely accommodated in all three types of disaster scenarios.

    The planning and construction of shelter is one of the important contents of the construction of disaster prevention ability. In the discussion of the key problems in the preparation of urban comprehensive disaster prevention planning, Wang Jiangbo, a Chinese scholar, puts forward that "the relationship between disaster risk and disaster prevention ability is like the relationship between spear and shield." Ideally, the two should be proportional, that is, the higher the risk of disasters is, the stronger the city's ability to prevent disasters will be [2] ". This paper puts forward that the response of shelter to disaster risk is mainly reflected in "adaptability", that is, in the face of the threat of natural disasters, under the premise of respecting the objective law of natural disasters, to give full play to the subjective initiative[3]. The connotation of "adaptability" is particularly prominent in the planning and layout of long-term shelters: first, long-term shelters should ensure the dual protection of the safety of places and the safety of the environment when people live in shelters after disasters. It is not only necessary to emphasize the disaster prevention ability of shelter sites or building structures, but also to withdraw from high disaster risk areas to avoid the hidden dangers of secondary disasters and secondary disasters. Second, to increase the capacity of medium-and-long-term shelters in low-risk areas to ensure the effective reception of the evacuated population in high-risk areas.

    The core content of this paper is whether the distribution of earthquake, storm surge and fire can "adapt" to the corresponding risks in coastal port cities. First of all, this paper combs the construction forms of all kinds of shelters, including the earthquake and fire prevention functions of park green space, as well as the moisture resistance function of building shelters. Then the principle of "evasive adaptation" of long-term shelter layout to disaster risk is put forward. Based on this, an empirical study on the local representative area of a coastal port city in China is carried out. Firstly, GIS spatial analysis software is used to visualize the distribution of alternative land use and disaster risk distribution of existing shelters, and then by comparing them one by one. This thesis summarizes the existing "adaptation" problems, and finally puts forward some improvement or optimization strategies.

    2 Types of Shelters

    The form of shelters determines whether they are defensive against a particular type of disaster, as shown in table 1:

    For earthquake defense, park green space can not only avoid the destruction of building facilities and ground pavement, play the role of physical disaster reduction of vegetation, but also accommodate large-scale motor vehicles and heavy machinery equipment in and out of parking. Park green space is also easy to set up tents and set up a multi-purpose apron, green space can also play the role of psychological comfort of vegetation landscape and so on. Earthquake shelters with a certain scale of open space can also improve the long-term accommodation of refugees.

    Large park green space is decisive for fire prevention. According to the experience of Japan from the Kanto earthquake and the Hanshin earthquake [4], it can be seen that only when the open space reaches 10 hm2, can the internal area be guaranteed to be safe. In addition, when the large park green space is used as a fire shelter, there are higher requirements for the external protection and isolation of the plant configuration. At present, the Japanese "FPS" planting method is widely used, as shown in figure 1. The park is divided into fire hazard zone (F), fire forest belt (P) and activity space (S) from the outside to the inside. In F area, the tree species whose trunk is difficult to catch fire and leaves are difficult to burn immediately should be selected, and the selection of plants in P area should be dominated by tree species with higher fire resistance than those in F area, and trees and shrubs should be properly planted to improve the coverage rate of the shelter. Plant general garden plants in area S as needed. [5] in addition, in order to enhance the disaster prevention effect of vegetation three-dimensional configuration and enrich the landscape level, the improved FPS model can also be used (figure 2). However, the park green space does not have the ability to resist storm surge. At this time, refugees must evacuate to high places. Therefore, reinforced concrete (or reinforced) structures and public service buildings with shockproof, wave-proof, wind-proof become ideal storm-surge shelters.

    3 The "Evasive Adaptation" Principle of Long-term Shelter Layout and Disaster Risk

    Disaster danger in a broad sense refers to disaster risk, including two dimensions: disaster risk and vulnerability of hazard-bearing body. The narrow sense of disaster danger only refers to the risk of disaster, which is formed by the joint action of hazard-causing factors and hazard inducing environment, which is manifested in the possibility, frequency, intensity, scope and time of disaster occurrence. This paper mainly studies the narrow sense of disaster risk.

    "Adaptation" to disaster risk is one of the many manifestations of disaster prevention ability, the most critical connotation of which is the trade-off between respecting the objective law of natural disasters and giving full play to the subjective initiative of human beings. When the impact of a disaster can be avoided or controlled, to adapt disaster is to resist the disaster; when the inevitable or the impact is uncontrollable, the "adaptation" disaster is the "avoidance" of the disaster.

    As far as population asylum operations are concerned, "adaptation" to disaster risk is to ensure emergency asylum in high-risk areas, but evacuate high-risk areas and transfer to low-risk areas as soon as conditions permit, rather than staying in high-risk areas for long periods of time. In other words, the layout of long-term shelters to accommodate post-disaster shelter life should abide by the principle of "evasive adaptation" to disaster risks: first, long-term shelters are mainly distributed in low-risk areas to ensure the dual safety of the place of shelter and the environment; Second, to ensure that the capacity of long-term shelters is redundant and capable of receiving large numbers of refugees transferred from high-risk areas. These two points will make the long-term shelters no matter from the spatial distribution or the scale of construction, all show a high concentration to the low-risk area.

    4 Research Method

    4.1 Disaster Risk Index and Evaluation

    As shown in table 2, due to the high degree of soil salinization in coastal areas, soil liquefaction is more likely to cause more serious damage to ground pavement and construction facilities in earthquake risk evaluation. Therefore, in addition to earthquake intensity, soil liquefaction should be used as an important earthquake risk evaluation index. In storm surge risk evaluation, flooding depth is positively correlated with topography, while waterfront loss means that when a river becomes a flood corridor for seawater to flow inland, the flow velocity along the river is higher than that in other areas at the same flooding depth. Previous studies have shown that the damage degree of buildings and facilities along the river 1km is obviously greater [6]; In the risk evaluation of industrial fires, although the port areas where dangerous production activities and equipment and materials are concentrated, serious fires will be caused by oil and gas leaks and explosions. However, high density planting and large area protection forest play a significant role in inhibiting the growth of fire and preventing the spread of fire.

    The index system evaluation method [7] was used to evaluate the risk of each disaster. Firstly, the main road of the city is taken as the boundary to divide the street block unit [8], then the scores of each index are calculated according to formula (1), and the scores are brought into the same unit scale through data standardization. Finally, the comprehensive evaluation value of each disaster species is obtained by equal weight summation of indicators. According to the American scholar Prasad (2016)'s discussion on the appropriateness of assuming that the weights of the indexes are equal, this paper assumes that each evaluation index has the same weight. It is not only conducive to providing a more comprehensive basis for physical geography and urban construction for the improvement of the distribution of storm surge shelters. It is also convenient to provide a replicable method which is easy to calculate for the planning research in similar areas.

    4.2 Identification of Spatial Distribution of Disaster Hazard

    Formula(1)

    Within the block unit, the ratio of the land area (Si) of each grade to the total area

    (S) of the unit and the sum of the products of this grade value (Li).

     

    After the results of disaster risk assessment are obtained, the spatial cluster analysis of earthquake risk, storm surge risk and industrial fire risk in the study area are carried out by ArcGis10.2 hot spot analysis (Hot Spot Analysis) to identify distribution differences between high and low values. In the results of hot spot analysis, the distribution of high value (hot spot) and low value (cold point) is statistically significant. Taking "hot spot" as an example, its characteristic is that first of all, the evaluation unit itself is of high value, secondly, it is surrounded by other evaluation units of the same high value.

    4.3 Identification of Spatial Distribution of Long-term Shelters

    In this thesis, ArcGis10.2 Kernel Density is used to calculate the weighted density of the sizes of various alternative shelters in the neighborhood of 2,000 m (this paper uses the size of occupied land) and obtain the overall distribution of the number and area of shelters in the study area. Previous studies have shown that 2,000 m is the maximum walking range under emergency response conditions. Failure to support effective walking activities beyond 2,000 m will drastically reduce the service capacity of long-term shelters. Therefore, it is reasonable to consider 2,000 m as the neighborhood of kernel density in a long-term shelter.

    5 Empirical study

    5.1 Research Areas and Data Sources

    A coastal port city in China is located in the key monitoring area of seismic activity, and it is also one of the most frequent storm surges in China. This city integrates manufacturing, energy, storage, logistics, residence and service, and it is a typical representative of China's comprehensive modern port city area, as shown in figures 3. The study area includes the eastern port area, inland river coastal area and northwest inland area in the core area of Binhai New Area, covering 410 km2 and 292 block units divided by urban trunk roads. According to table 1, the existing land is extracted, of which 185 are alternative sites for long-term storm surge shelters. 97 alternative sites for long-term fire shelters; 282 alternative sites for long-term earthquake shelters.

    Since the alternative land for the long-term earthquake shelter is the sum of the alternative land for the long-term storm surge shelter and the long-term fire shelter, the following discusses the adaptation of storm surge and fire first, and finally discusses the risk adaptation of the long-term earthquake shelter.

    5.2 Long-term Storm Surge Shelters and Storm Surge Hazard Distribution Results

    The spatial distribution of alternative long-term storm surge shelters is very uneven and concentrated in the north-west inland (Fig. 4-1). Although there are many storm surge shelters in the central region, but due to construction saturation, land shortage, high land prices and other reasons, public service facilities generally cover a small area. On the contrary, in the north-west inland, the distribution of large-scale educational and scientific research land in groups has become the main reason for the high kernel density and concentration of long-term storm surge shelters.

    The risk distribution of storm surge also shows significant spatial differentiation, with the highest risk in coastal and inland river estuary areas, which is due to the low offshore topography, and increases the possible immersion depth of storm surge (Fig. 4-2). In addition, the large-scale reclamation extends the urban construction land to the sea area, so that the possible flooding range of storm surge becomes larger. The narrow docks of inland river and port constitute storm surge flood corridors, which will increase the loss of coastal water.

    5.3 Long-term Fire Shelter and Fire Risk Distribution Results

    The alternative long-term fire shelter is mainly affected by the layout of the regional ecological corridor, mainly concentrated on the western edge of the scope of the study. However, in the internal area, because of the high building density and less green space in large parks, fire shelters have the low distribution of kernel density (figure 5-1).

    The distribution of fire risk also shows significant spatial differentiation, coastal and port areas have the highest disaster risk, which is because there are dangerous enterprises in the port area, and there are a large number of flammable and explosive goods stored in the storage logistics land, so the hidden danger of fire and explosion is very great. In addition, compared with the inland living concentration area, the port area industrial large-scale park green space construction is insufficient, but also makes it lack of fire and moisture-proof function (figure 5-2).

    5.4 Long-term Earthquake Shelter and Earthquake Risk Distribution Results

    As shown above, the combination of alternative long-term storm surges and fire shelters equals alternative long-term seismic shelters, so their spatial distributions are characterized by a combination of the two-mainly concentrated in the north-western interior, which depend on large park green space, sports land, education and scientific research land to form together (figure 6-1). The distribution of seismic risk shows significant spatial differentiation. The large-scale coastal area is a marine sedimentary area, with totally high degree of soil salinization, and is affected by the intersection of seismic zones, so the ground motion parameters are high. Overall, coastal areas show a higher risk of earthquake-induced disasters than inland areas in the north-west (figure 6-2).

     

    6 Discussion and Conclusion

    First, the centralized distribution of long-term shelters can effectively avoid the high-risk areas of storm surge disasters, but its scope of influence is limited. There are three long-term storm surge shelters, all of which are composed of educational and scientific research facilities and are located in low-risk areas. However, the scope of its services is too concentrated to make full use of the wider range of low-risk areas, which may also lead to the transfer of the population from high-risk areas to low-risk areas and cannot be fully accommodated.

    We can optimize the adaptability of long-term storm surge shelter layout to storm surge risk by slowing down the risk of storm surge disaster and increasing the distribution of storm surge shelter. First, we can set up tidal disaster protection forests on both the coastline and the inland waterfront. In order to improve the landscape quality and add the attributes of public activities, shelterbelts, sponge facilities and park green space are arranged in combination. Second, the low risk area is mainly located in the central and peripheral areas of the study area. At this stage, there is still a lag in the matching of public services in this area, but there are still more urban construction land resources. We should make full use of low-risk areas to vigorously supplement culture, welfare and other public service supporting facilities, ensure people's livelihood, at the same time, expand the scope of the concentrated distribution of storm surge shelters. At the same time, due to the saturation of construction in the central area and the very high land price, it is ineffective to greatly increase the density of storm surge shelters through the construction or expansion of existing public service facilities. At this time, commercial service facilities can be included in the designated scope of storm surge shelters, which requires the government to sign pre-disaster agreements with the owners and managers of commercial service facilities, then through financial incentives or volume rate incentives to encourage the participation of business services.

    Secondly, for fire, the main distribution of long-term shelters can avoid high-risk areas, but its scope of impact is not only limited, but also marginalized. There are two concentrated distribution of long-term fire shelters, both of which rely on the formation of regional through ecological corridors. Among them, one large concentration distribution is located in the low risk area, while the other small concentration distribution is located in the high risk area. Overall, the impact of centralized distribution is too limited and marginalized to make full use of a wider range of low-risk areas, while at the same time it may lead to the evacuation of population from high-risk areas to low-risk areas and unable to be effectively accommodated.

    We can optimize the adaptability of the layout of long-term fire shelters to fire hazards by reducing the disaster risk and increasing the distribution of fire shelters. First, fire and explosion-proof forest belts [10] should be added between high-risk areas and low-risk areas, which can be arranged along high-grade roads such as external traffic, and large urban parks should also be connected in series, which constitutes an urban green corridor with both ecological disaster reduction function and landscape leisure function. At the same time, we should increase the threshold for dangerous enterprises to enter the northern industrial park. Enterprises of level 5 or above (dangerous goods classification method) and CD enterprises (safety production classification method) are not allowed to be stationed and strengthen the disaster risk management system and fire control ability. Second, we can increase the open space scale and greening rate of educational and scientific research land in the inland southwest region, strengthen the three-dimensional and group allocation of land plants, and improve its ability as a fire shelter.

    Thirdly, for earthquake disasters, the main distribution of long-term shelters can avoid high-risk areas, and it has a wide range of impact. Long-term storm surge shelter and long-term fire shelter together constitute a long-term earthquake shelter, no matter from the location or scale, the long-term earthquake shelter shows a strong seismic risk adaptability.

    Taking the local representative area of a coastal port city in China as an example, this thesis reveals the "adaptability" of disaster risk existing in the distribution of medium-and long-term earthquakes, storm surges and alternative land for fire shelters. The results not only show that the distribution of alternative land for all kinds of asylum places needs to be further improved, but also reflect that the existing urban environmental safety needs to be improved. The problem of "adaptability" cannot be fully solved by relying on the improvement of one side alone.

    Note: the land use planning data in the case area in this thesis do not come from the official planning documents. The analytical drawings in this paper are drawn by the author.

     

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    (整理:赵迪 译:张悦颍)

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