Cities are evolving systems. We have little understanding of their behaviour. We know that they are highly dynamic, in that they face changing environments and inputs, and adapt to these changes. Over a longer historical period, cities have always successfully adapted to changing environmental conditions and thus have been extremely resilient. From 1100 to 1800, only 42 cities worldwide were deserted after their construction.
Introduction
The year 2007 marks a turning point in history: half of the world population lives in cities (UN-Habitat, 2007). Moreover, the trend of rapid urban growth through the mid-20th century in the developed world has now shifted to the developing regions of Asia and Africa. Urbanisation has led to an increase of economic and social wealth in some places, but also to continuing poverty of others.
The urban population is expected to double from two to four billion over the next 30 to 35 years (United Nations, 2006). These growth rates imply that, every week, a city of one million inhabitants will be built for the next four decades. Unintended side effects of the concentration of the number of people exposed to floods are also increasing. Floods are much more frequent, wider and devastating than in former times, where societies developed more slowly and more robustly. Indeed, these trends suggest that citizens and urban communities are becoming more vulnerable to floods.
There is growing recognition in Europe as well as in most other continents of the world that current practice to manage urban floods needs to change. This paper briefly describes the drivers and underlying causes for change in more detail and explores possible avenues. of new sustainable approaches. Much information provided in this paper has been developed over the past four years by the European knowledge network COST C22 on Urban Flood Management. This network consists of more than 50 experts from 13 European countries willing to share their experiences, expertise and tools.
One of the missions of this network is to help to inform and engage stakeholders in promoting integrated and cooperative approaches in Urban Flood Management.
Lack of planning
The question arises of how we should dampen this increasing trend of flood vulnerability. Do we know enough to reveal the underlying processes responsible for this overall increase? Do we understand how cities grow and what the impact of autonomous growth will be on their susceptibility to floods?
The answer is unfortunately no. In any case, many of the theories of how cities function and grow have been developed in and for industrialized cities, although much of the urban growth of the 21st century is occurring in the developing world. Although comprehensive and systematic research is still lacking, a number of studies substantiate the general assumption that urbanization is largely an uncontrolled process. Based on estimates of the United Nations, only 5 percent of new development ‘under way’ in the world’s expanding cities is planned.
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Urban growth of the city of Hydrerabad (1990 and 2000) showing two substantially different forms of urban expansion (through ‘infill’ of the remaining open spaces in already built-up areas and through ‘outspill’ in areas previously in non-urban use)
This lack of careful planning, or even uncontrolled planning, will exacerbate the trend of increasing flood vulnerability of cities due to a combination of the following factors:
These trends pose new challenges for urban flood research and for research into urban planning. Because one cannot manage urban floods in isolation, there is a need for integrated approaches which address different spatial scales, ranging from catchment to urban communities and their interactions. We know very little about these interactions or how they might affect flood vulnerability of cities.
{sidebar id=289 align=right} Although the projected impacts may be marginal increases on the already large flood losses in the coming next decades, climate change will probably have a major impact on the way in which we deal with flooding on the longer term. Countless studies show that we should start now to adapt to climate change, to prevent costly emergency interventions in the future. This means that flood risk management strategies must meet present needs, while providing an adjustment path for the future.
For example, if governments were taken no actions the UK population at risk will increase from 1.6 to 3.6 million and the cost for flood defences will increase from 3.9 to 48 million pound by 2080 (Foresight, 2005). In this connection, transition and developing countries could learn from the mistakes of developed countries, which have already made the transition from agricultural to industrial, service-based economies.
The first group is not yet stuck on past investments and, consequently, has greater freedom of movement. Although caution has to be taken, in certain situations it would also be possible to leapfrog western technology.
Act of God or neglect of men?
Flood management policies changes over time. The transition is a process of predominantly incremental change and reactive responses to flood disasters or narrow escapes have acted as catalysts for accelerating this process.
An important notion is that current flood protection measurers are based on the accumulated knowledge of past weather events: climate change is perceived as a stationary process (the past reflects the future). Major flood disasters have created the need to shift from flood protection to a more integrated approach. In the last decade, however, climate change is recognized as a potential trend breaker, in the way that hydrological variables and existing statistical distributions on flood probabilities are addressed. The present challenge seems to be that we must recognise that the future is inherently uncertain and that science will not necessarily reduce uncertainty.
The long-term horizon of climate change and current scientific uncertainties pose special challenges. Strategies which address these challenges have in common that they recognize that there is no best solution but embrace a future which fits into a distribution of events that will not come as a surprise. In that sense, climate change provides new incentives for the need to plan ahead and to anticipate extreme events.
Towards transition
The challenge to address urban floods and to reduce urban flood vulnerability has received little attention. This is partly because in the traditional flood management approach responses to mitigate urban flood risks have been often set outside the realm of the urban system (e.g. where confined at the catchment level) and responses at city level if any were predominantly passive using robust solutions such as urban defences and increasing the capacity of major culverts.
The following major bottlenecks were identified, which hampered the adoption and effective implementation of flood risk management into the urban planning practices:
i) Lack of understanding of current and future risks and implications at city scale;
ii) Lack of long-term planning, poorly integrated and comprehensive planning;
iii) Inadequate controlling roles of local and regional authorities, and the conservative nature of the building sector.
It follows from the above that traditional flood-risk management approaches omit important ways of dealing with floods pro-actively at city level, of building in responses that reduce their impact and enhance recovery. Dealing with these gaps should change the paradigm of the traditional approach as listed in Table1.
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There is still a long way to go to bridge the gaps between strategy, the enabling institutions and practice. This emphasizes the need to address the underlying processes that enforce the transition. A major constraint for this transition is a widespread underestimation of the complexity of the transition process itself. The process that leads to adoption of these innovative views and approaches on city scale has only just started and research in this field is very limited. There are, however, a few examples, such as UFM -project, which are now generating their first results.
The UFM-project entails a multiple scope that includes: (i)an innovative practical approach with stakeholder participation, leading to an urban flood management plan. In this participatory approach, promoting local innovation is not considered primarily an approach to research, but rather an approach to engagement and capacity building; (ii)applied research on models, methodologies and concepts (such as flood risk and vulnerability assessment, flood risk maps), technologies (such as flood-proofing buildings and infrastructure), planning and building regulations; (iii)experience and knowledge exchange and dissemination between the partner cities and other professionals and scientific networks.
{sidebar id=305 align=right} The city of Dordrecht, which is situated on an island, is confronted with the challenges of how to manage changing flood risk in its redevelopments and expansions in at-risk areas outside the primary flood defence system. The first project results reveal that the consequences of flooding in these built-up areas could be minimised through relatively simple individual flood proofing modifications of traditional buildings and infrastructure.
Since these built-up areas may provide a save shelter for the citizens of Dordrecht in case of an exceptional flood (c.q. above design level which may result in a flood exposure of a large and densely part of the city area behind the flood defence), the envisaged master plan will also include the design of structures (such as high rise buildings) that could be used for vertical evacuation of large populations.
The above mentioned projects conform strongly to the notion that local scale pioneering and experimentation are essential and encourage the belief that these bottom-up initiatives can shape strategy and policy development to cultivate urban flood resilience. Moreover, the first experiences show that local government is well placed (providing they have the capacity to do so) to act as a facilitator between the senior government, local stakeholders, and the private sector.
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Chris Zevenbergen, Chair COST C22 on Urban Flood Management
For more Information: www.COST22.org
