Berry Gersonius

Developing the evidence base for mainstreaming adaptation of stormwater systems to climate change

In a context of high uncertainty about hydro-climatic variables, the development of updated methods for climate impact and adaptation assessment is as important, if not more important than the provision of improved climate change data. In this paper, we introduce a hybrid method to facilitate mainstreaming adaptation of stormwater systems to climate change: i.e., the Mainstreaming method. The Mainstreaming method starts with an analysis of adaptation tipping points (ATPs), which is effect-based. These are points of reference where the magnitude of climate change is such that acceptable technical, environmental, societal or economic standards may be compromised. It extends the ATP analysis to include aspects from a bottom-up approach. The extension concerns the analysis of adaptation opportunities in the stormwater system. The results from both analyses are then used in combination to identify and exploit Adaptation Mainstreaming Moments (AMMs). Use of this method will enhance the understanding of the adaptive potential of stormwater systems. We have applied the proposed hybrid method to the management of flood risk for an urban stormwater system in Dordrecht (the Netherlands). The main finding of this case study is that the application of the Mainstreaming method helps to increase the no-/low-regret character of adaptation for several reasons: it focuses the attention on the most urgent effects of climate change; it is expected to lead to potential cost reductions, since adaptation options can be integrated into infrastructure and building design at an early stage instead of being applied separately; it will lead to the development of area-specific responses, which could not have been developed on a higher scale level; it makes it possible to take account of local values and sensibilities, which contributes to increased public and political support for the adaptive strategies.

Multi-objective optimisation of cost–benefit of urban flood management using a 1D2D coupled model

This paper presents a multi-objective optimisation (MOO) tool for urban drainage management that is based on a 1D2D coupled model of SWMM5 (1D sub-surface flow model) and BreZo (2D surface flow model). This coupled model is linked with NSGA-II, which is an Evolutionary Algorithm-based optimiser. Previously the combination of a surface/sub-surface flow model and evolutionary optimisation has been considered to be infeasible due to the computational demands. The 1D2D coupled model used here shows a computational efficiency that is acceptable for optimisation. This technological advance is the result of the application of a triangular irregular discretisation process and an explicit finite volume solver in the 2D surface flow model. Besides that, OpenMP based parallelisation was employed at optimiser level to further improve the computational speed of the MOO tool. The MOO tool has been applied to an existing sewer network in West Garforth, UK. This application demonstrates the advantages of using multi-objective optimisation by providing an easy-to-comprehend Pareto-optimal front (relating investment cost to expected flood damage) that could be used for decision making processes, without repeatedly going through the modelling-optimisation stage.

Managing flood risk in the urban environment: linking spatial planning, risk assessment, communication and policy

Over recent years there have been a number of attempts at integrated approaches being taken to water and flood risk management. Recent flooding events in Europe have triggered discussions about giving rivers back their nature (floodplains in stead of dikes). However, the emphasis tends to be on finding space for flood water in rural areas in order to protect the urban areas. The question how to deal with major floods in urban areas has not received much attention, and as yet the delivery of increased system resilience as defined by de Bruijn (2005) is a major challenge. In a resilient approach the focus is on accommodating flood waters, with concurrent impact minimalization and rapid recovery. Spatial solutions (diversification of defense levels for different land uses according to their vulnerability) may provide important opportunities to reduce flood impacts, whereas flood proofing of buildings enhances the recovery capacity of the system. In this paper it is argued that cities play an important role in driving the transition to adaptive flood management approaches across different spatial and temporal scales. Yet, at the moment there are a number of bottlenecks which have so far hampered the adoption and effective implementation of flood risk management into urban planning practices. As such the recent Urban Flood Management (UFM) project, which aims at the development and verification of UFM strategies and methodologies in the cities of Dordrecht, Hamburg and London, may provide relevant practical examples to address these issues. These experiences could contribute to national and European policy making, such as input for the EU Flood Directive. This paper discusses the background and challenges to the UFM project, and also shares the first insights from this international umbrella project.

Adapting to climate change: using urban renewal in managing long-term flood risk

Cities are dynamic systems. Understanding the role of time and the way it shapes the urban fabric and structure is crucial to assess urban flood vulnerability and to manage the capacity of cities to adapt to changes in demography as well as in climatic conditions. Consequently, cities have to learn from the past and anticipate the future in order to develop and implement effective flood management approaches. They have to eliminate unsatisfactory practices through investigation, experimentation and evaluation. Urban renewal of buildings and infrastructure is one of the means by which cities adapt to long term changes, to correct old errors and to increase flood resilience. According to the latest climate change scenarios flood frequency is going to increase significantly over the lifetime of existing buildings. Therefore, the inclusion of pro-active retrofitting in regular urban renewal schemes and decreasing lifetime cycles of new buildings are likely sound and effective strategies to increase the robustness of the urban fabric to climate change. Since current building practices are based upon the assumption that the built environment will not experience significant change, these approaches will have major ramifications for investment levels and building methods. In order to account for the relatively rapid rate of substitution of buildings and other built structures it is argued in this paper that the life cycle assessment and full cost accounting of the building stock should be included in the development of effective UFM strategies.

Coping capacities for improving adaptation pathways for flood protection in Can Tho, Vietnam

The planning and phasing of adaptation responses are essential to tackle uncertainties and ensure positive outcomes while adapting to changing circumstances. Understanding the evolution of coping and adaptation responses and their capacities is a prerequisite for preparing an effective flood management plan for the future. The aim of this paper is to determine the effect of coping capacity on longer term adaptation responses in a flood risk management system. The objectives, requirements, targets, design, and performance of flood protection measures will have to be determined after taking into account, or in conjunction with, the coping capacities. A methodology has been developed and demonstrated based on an adaptation pathway approach to account for coping capacities and to assess the effect of these on flood protection measures. Application of this methodology for flood protection measures in Can Tho City in the Mekong Delta shows the effect of considering coping capacity for flood protection measures and the value in delaying the occurrence of tipping points. Coping measures such as elevating property floor levels can postpone the tipping points when dikes are no longer effective. Consideration of coping capacity in the system improves adaptation responses and leads to better adaptation outcomes.

Adaptive Delta Management for flood risk and resilience in Dordrecht, The Netherlands

Many countries across the world are experiencing strict austerity measures due to the economic crisis. As a consequence, public financing for stand-alone adaptation to flooding and drought will become scarcer in the (near) future, and this hampers the pursuit of resilience (i.e. the ability to remain functioning under a range of hazard magnitudes). In such times, key challenges for adaptation are further complicated by weaker investment dynamics and an increased tendency to ‘work in silos’. These are: to minimise regret with respect to maladaptation, which results from over- or under-investment in water hazard management; to exploit the opportunities for mainstreaming adaptation to flooding and drought into other investment agendas; and to deliver multiple benefits for society and the economy, such as increased biodiversity, liveability and competitiveness. These common challenges drive the best way in which to adapt to uncertain climate and socio-economic changes. In the Netherlands, the Delta Programme has developed and applied a structured and well-defined approach (called Adaptive Delta Management) for including and acting upon uncertainty around these future changes. This approach allows for greater transparency to decision-makers and stakeholders, because it adheres to four specific steps for strategy development. This paper presents the current understanding of Adaptive Delta Management and an illustration of the approach for the management of flood risk and resilience in Dordrecht. It examines the added value and limitations of Adaptive Delta Management concerning its application in the context of the Delta Programme, with a specific emphasis on the lessons learned from Dordrecht.

Assessing quick wins to protect critical urban infrastructure from floods: a case study in Bangkok, Thailand

This paper focuses on the vulnerability and protection of critical urban infrastructure from flooding. It presents a pragmatic and rapid screening procedure, referred to as a “Quick Scan”. The purpose of the Quick Scan is to provide guidance for network operators and decision makers on identifying and rating those critical infrastructure networks and hot spot buildings that may be at risk from flooding and assessing where intervention will be most feasible and cost beneficial – the so-called “quick wins”. This approach will support the development of effective interventions to alleviate direct and indirect flood impacts. Workshops and interviews with stakeholders and experts have been organised in the pilot cities Bangkok, Paris, and Dordrecht to test and further develop the Quick Scan and to obtain feedback and lessons learned for the protection of critical urban infrastructure. This paper presents the findings of the stakeholder workshops carried out in the city of Bangkok.

Toward a More Flood Resilient Urban Environment: The Dutch Multi-level Safety Approach to Flood Risk Management

The new EU Floods Directive requires flood risk reduction for areas where risk is deemed significant; for these zones, flood risk management plans must be prepared. In line with these requirements, the Netherlands has opted for a ‘multi-level safety’ approach, which includes prevention, protection and preparedness responses. This paper describes the application of the multi-level safety approach to the case of the Island of Dordrecht in the Netherlands. For this case study, the flood risks were mapped based on flood depth and arrival time. The results of the risk mapping show that nearly the entire island is at high-risk. A further area perspective map recommends focusing on national- and regional-scale measures for the Island of Dordrecht. Following these results, this paper examines the effectiveness of two alternative regional-scale responses to flood risk reduction: On the one hand, the complete reinforcement of the primary dike ring, and on the other, a partial reinforcement together with a compartmentalisation dike. It is shown that both options can significantly reduce the expected annual damages and number of casualties. The cost-efficiency of each has also been investigated. In this regard, it is concluded that the combination of a partial reinforcement and a compartmentalisation dike is economically feasible.

Resilient flood risk strategies: Institutional preconditions for implementation

textabstractThere is a growing recognition of resilience enhancement as an additional objective for adaptation. This will typically involve enhancing the preparedness and capacity to respond to the impacts of climate change. Within flood risk practice, resilient strategies focus on reducing impacts from flooding through better prevention and preparedness. Such strategies will not only reduce existing risk levels, but could also make the social-ecological system more robust for extreme flood events. This is because they seek to prevent those impacts on the system from which recovery is extremely difficult without outside help. Besides that, resilient strategies increase the prospect for the realization of cobenefits, particularly when measures are selected within the spatial domain. Implementing resilient strategies, however, faces many difficulties, particularly in countries like the Netherlands and Poland where prevalent governance arrangements are aimed to facilitate resistant strategies, focusing exclusively on flood protection. We analyzed these implementation difficulties for the Island of Dordrecht, which is a front-runner case of resilient flood risk governance in the Netherlands. A theoretical framework based on relevant issues regarding governance arrangements was used to reflect on the identified gaps and barriers. Although all issues played a role in the case study, there seem to be no generic institutional design parameters that have to be applied for implementing resilient strategies. Even in the current institutional regime, it is possible to find ways of implementing a resilient strategy. The more general institutional precondition has to do with the political willingness to allow for collaboration and experimentation and to enable a more flexible use of current principles and rules.

Multi-criteria Approach for Selection of Green and Grey Infrastructure to Reduce Flood Risk and Increase CO-benefits

Continuous changes in climate conditions combined with urban population growth pose cities as one of the most vulnerable areas to increasing flood risk. In such an atmosphere of growing uncertainty, a more effective flood risk management is becoming crucial. Nevertheless, decision-making and selection of adequate systems is a difficult task due to complex interactions between natural, social and built environments. The combination of green (or sustainable) and grey (or traditional) options has been proposed as a way forward to ensure resilience in advance of extreme events, and at the same time to obtain co-benefits for society and the environment. The present paper describes a novel method for selection of urban flood measures, based on a multi-criteria analysis that includes flood risk reduction, cost minimization and enhancement of co-benefits. The aim of this method is to assist decision makers in selecting and planning measures, which afterwards can be part of either high level scoping analysis or more complex studies, such as model based assessment. The proposed method is implemented within a tool which operates as a standalone application. Through this tool, the method has been applied in three study cases. The findings obtained indicate promising potential of the method here introduced.