Can farmers extend their cultivation areas in urban agriculture? A contribution from agronomic analysis of market gardening systems around Mahajanga (Madagascar)

The rapid urbanization in developing countries implies an increasing pressure on urban agriculture for production. As most perishable food products come from this agriculture in close proximity to population concentrations, we analysed from an agronomic point of view how market-garden farmers can meet this increasing urban demand. This work took place in the case of Mahajanga, a secondary city with high increasing demographic rate on the Northwest coast of Madagascar. Based on preliminary surveys to characterize the farming systems (on a sample of 91 farms), 11 market-garden farmers chosen in the three main agricultural zones of the urban area were surveyed during two years. Surveys aimed at understanding their decision rules in crop choices, crop allocation to land and resource management, and to estimate their room for manoeuvre to increase their leafy vegetable areas under cultivation. The wholesalers and retailers who buy the farmers’ produce were also surveyed. A previous model of decision rules regarding crop location on farm territory was used to analyse the on-farm surveys and cartographic methods (GIS and on-farm manual representations) were used to quantify the land use. We highlight the following major points. (1) The leafy vegetable production in the surveyed farms already intensively uses land: farmers have complex decision rules largely depending on the water dynamics in the two main environments (lowlands and lakesides) where leafy vegetables are cultivated during the dry season. (2) The scarcity of farmers’ resources (labour money and water) leads to very little internal room for manoeuvre to increase the leafy vegetable production in the farms. (3) At territorial level however, some land reserve exist in one of the lowlands, but not on lakesides. The water availability for agriculture must be better informed through specialized hydrologic studies, as one of the main constraints nowadays to extend the agricultural area. An extrapolation to other cases of urban agriculture is then discussed as well as the role of agronomy to help urban planners to consider the place of agriculture in the urban development.     

完善我国城市房屋拆迁补偿范围的思考

城市房屋拆迁的补偿范围是拆迁活动的核心内容,补偿范围不全面,拆迁矛盾便不能得到根本解决.我国城市房屋拆迁补偿范围过于狭窄,土地使用权没有完全补偿.文章针对目前拆迁补偿范围存在的问题进行分析,提出了完善补偿范围的相应对策.     

围绕生态城市目标规划城市绿地系统

通过对普兰店市城市绿地系统规划建设案例的分析总结,探讨了当前县域城市绿地系统规划建设的发展方向,并从城市绿地系统布局、保护城市生态系统的生物多样性和原有环境、完善法规制度等方面提出了城市绿地系统规划的建议.     

检视都市永续发展指针的发展历程与内涵:从指针系统建构到政策评估

本文回顾国际上相关的都市永续发展指针系统,探讨指针系统架构与内涵之间的差异,进而说明永续台湾评量系统中"都市台湾"指针系统的重要特色,以及指针项目选定的理论基础.藉由永续台湾评量系统中22个范畴的型态辨识,本文分析了都市在台湾永续发展中所扮演的角色,确认都市生产与生活型态对于整体永续发展的重要性,也验证了生态系统观点中都市对于环境的依存与影响.考量都市发展决策过程需要永续性的评量机制,本文利用都市永续发展指针作为政策评估的重要变量,应用交互式计算机软件<感受性系统模型(Sensitivitv Model Tools)>以系统性观点进行都市发展政策永续性的评析.透过系统软件功能掌握变量结构的完整性以及系统变量之间的相互影响关系,并藉助于团体咨询与讨论的沟通方式建构半量化的(semi-quantitative)系统变量,配合概念化及模糊化的方式界定变量水准以及函数关系进行系统仿真工作.籍由系统仿真了解变量之间的互动关系,而政策评估案例分析显示台北市硬件建设政策较空间调整政策发挥较大的效果.永续指针与系统工具的结合整体而言提供了都市政策永续性评估的沟通与预测接口.     

环境规制对资源型城市转型非线性影响

为探究环境规制、资源型城市转型及其空间资源溢出间关系,从空间溢出视角出发,在2011—2021年的113个资源型地级市数据基础上,构建半参数门限空间杜宾模型(STSDM),探索了环境规制对资源型城市转型绩效的非线性关系及其非对称性空间溢出影响。结果表明：①线性假设下环境规制不利于城市转型绩效提升,但非线性假设下,环境规制在初期有利于资源型城市转型绩效提升,具备有“边际效应递减”的非线性长期特征,偏导图呈弱“U形”特征;②资源型城市转型绩效在空间资源溢出效应上存在有非对称性;③资源型城市环境规制处于越高阶段,能够获得城市绩效转型的空间资源溢出红利越少。据此提出要因地适宜设立环境规制政策、建立长效环境保护机制等政策性建议。     

创新要素流动对城市群协同创新的影响——基于长三角城市群与长江中游城市群的实证

利用2006-2017年长三角城市群和长江中游城市群共41个地级市面板数据,首先,运用拓展DEA法对两大城市群协同创新水平进行测度,然后,采用空间计量模型实证考察创新要素流动对城市群协同创新的影响,进一步以互联网发展水平为门限变量,构建门限模型,探析互联网发展对创新要素在城市群流动的协同创新效应是否存在门限效应。研究发现：创新要素流动对城市群协同创新影响的总效应显著为正,空间正向溢出效应显著,且存在群际差异;在两大城市群内,创新要素流动对城市群协同创新影响呈现非线性,创新人员流动对城市群协同创新影响呈“倒U型”特征,创新资本流动对城市群协同创新影响呈“U型”关系,相应拐点在不同城市群呈现异质性。     

区域一体化与城市创新：基于长三角扩容的准自然实验

随着我国城市进入都市圈发展的新时代,区域一体化对城市创新产生了广泛而深刻的影响。从创新资源流动整合、知识技术溢出和市场规模扩大等维度深入分析区域一体化对城市创新的潜在作用机制,将长三角扩容作为一项准自然实验,以2003-2018年中国内地283个地级市为样本数据,综合利用合成控制法和PSM-DID模型对两者关系进行实证检验。结果发现：①整体而言,长三角扩容能够显著促进城市创新水平提升。从不同区域看,长三角扩容对原位和新进城市创新水平均有显著促进作用,且对新进城市的影响大于原位城市;②异质性分析结果表明,扩容政策对科创走廊城市创新水平的提升作用强于非科创走廊城市,同时区域通达性改善也能够明显强化扩容对城市创新的政策效应;③扩容政策对城市创新的作用呈现出边际效应递减趋势。研究结论对推进长三角一体化发展、深化区域创新合作、建设长三角创新驱动示范带具有重要指导意义。     

城市轨道交通相邻多车站动态协同限流研究

为应对城市轨道交通车站高峰期客流压力,限流已经成为常态应对措施,而经常采用的限流策略大多针对单个车站,缺少对相邻多个车站的协同考虑。基于客流在车站间的传播效应,以乘客总延误时间最小为目标,以站台及列车能力为约束条件,构建城市轨道交通相邻多车站协同限流决策模型,同时为实现实时动态控制,引入滚动时域控制方法,优化多车站动态协同限流流程。以北京地铁8号线为例,经过相邻若干车站运营数据进行限流策略计算。结果表明,该模型限流可以在不造成车站服务人数损失的同时,将乘客总延误时间降低21%。     

考虑换乘费用的城市公共交通票价优化

换乘所产生的附加费用,如时间和票价等,导致配流影响因素产生变化,如果沿用传统方式将降低预测精度和可靠性。通过引入换乘次数和方式等因子计算出行等待、乘车、换乘及风险评估预留时间等,定义广义出行费用与计算方法;建立双层规划模型求解最优票价,最后通过算例分析弹性出行需求、换乘费用、票价之间的关系。计算结果表明,换乘费用对出行需求的影响小于票价优化对出行需求的影响,优化票价随换乘费用增加而加速降低,为公共交通票价优化提供研究依据。     

Parking futures: Preparing European cities for the advent of automated vehicles

The introduction of automated vehicles (AVs) is a virtual certainty. Much less certain is the timing of their introduction and how rapid the transition to full automation will be. Various governments are already working to facilitate this shift by, for example, amending and elaborating regulations to support the introduction of AVs, or supporting tests in different urban environments. Meanwhile, urban and regional planners and decision-makers are still grappling with the uncertainties and differing opinions about the possible impacts of AVs on land-use changes and location choices, particularly in relation to the space available for vehicles, both moving (i.e. roadspace) and stationary (i.e. parking space). This paper uses a backcasting approach to identify critical policy decisions and measures to be taken before the implementation of AVs, so as to achieve a more desirable, attractive and high-quality city. These policy measures primarily relate to the reuse and reallocation of parking and roadspace. Two strategic decisions are found to be essential to meet the major goals of sustainable and liveable cities: a clear commitment to a shared mobility and the delimitation of Core Attractive Mixed-use Spaces (CAMS). In order to deliver these desired urbanisation patterns, a set of three policy paths, involving eight policy packages, is proposed for the next 20–30 years. This article provides urban and regional decision-makers with examples of interventions that can be implemented beyond and during the implementation of AVs.