Lessons learnt from adaptation planning in four deltas and coastal cities

Deltas and coastal cities around the world face the need to adapt to uncertain future changes. We compared adaptation planning on flood risk management in four cases based on three main elements of adaptive planning: to prepare for a wide range of plausible future scenarios; to respond to change with robust and flexible actions; and to monitor critical changes to be able to reassess the plan accordingly. Differences can be observed in the implementation of these elements. Good practices could be distinguished: cases consider a wide range of future scenarios; short-term decisions are coupled with long-term options while envisioning these options and possibilities for switching between them through adaptation pathways; opportunities originating from other agendas to achieve multiple objective investments are seized; and the system’s resilience is improved by a wide variety of measures. At the same time some barriers for using adaptive planning approaches were identified: the use of a wide range of scenarios is only accepted in an exploratory phase of planning. Structural flood protection measures taken in the past do constrain future choices. The potential for monitoring and reassessment of options is hampered by the fact that trends in some variables cannot be detected. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/). doi: 10.2166/wcc.2014.141 ://iwaponline.com/jwcc/article-pdf/6/4/711/600683/jwc0060711.pdf Ad Jeuken (corresponding author) Marjolijn Haasnoot Deltares, P.O. Box 177, Delft 2600MH, The Netherlands E-mail: ad.jeuken@deltares.nl Tim Reeder Environment Agency, London, UK Philip Ward Faculty of Earth and Life Sciences, Institute for Environmental Studies (IVM) and Amsterdam Global Change Institute (AGCI), VU University Amsterdam, Amsterdam, The Netherlands


INTRODUCTION
The world's river deltas and coastal cities are increasingly vulnerable due to pressures from climate change, relative sea level rise, and population growth (Mulder et  Therefore, in densely populated deltas and estuaries such as the lower Rhine delta in the Netherlands, the Thames estuary in the UK, the Hudson in New York, and the Ciliwung delta on Java (Indonesia), spatial planning is challenged to enable socioeconomic developments and well-designed water management to provide services such as flood risk management, fresh water supply, and good environmental conditions. Decisions on water management and spatial developments are needed to prepare for future changes. However, uncertainties about the future, the dynamic nature of deltas, and the interaction between the environment and society make such decisions less than straightforward. Decisions avoiding adverse impacts and seizing opportunities are preferred, as the implementation of actions takes time and some actions that may have been possible in the past or at present may not be possible in the future.
Plans are often crafted to operate within a certain range of conditions. But this traditional approach of engineering based on the assumption of a more or less stationary climate is quickly losing ground (Milly et al. ).
Experience demonstrates that if this range is too small, such plans have unintended impacts or do not achieve their objectives if the future turns out differently. In case of severe uncertainties (sometimes called deep uncertainties), robust policies and adaptive policies are needed. Robust policies perform well under a wide range of plausible futures, while adaptive policies can be adapted once the future unfolds differently than foreseen. Walker et al. () discriminate between static and dynamic robustness. The first can also be regarded as the robustness (Mens et al. ) of the (physical) system, the latter as the flexibility of the adaptation plan. In some studies (Wardekker et al. ), resilience is also regarded as a characteristic of the system under consideration. and policies, strategies, and structure plans are appropriately redefined. We add to this the element of 'no or low regret'.
No regret options in case of uncertainties are actions that have properties such as robustness, flexibility, and reversibility (Refsgaard et al. ).
More specifically, the following three main subquestions, reflecting the main elements of adaptive planning, are investigated using four case studies: (1) How is the 'widest set' of plausible future scenarios defined and used in the assessment of strategies within the four cases?
(2) How are robustness and flexibility being considered? Are actions chosen to remain flexible with respect to uncertain future changes and/or to create a robust system that may better cope with extreme events? In other words, how is 'low regret' of decisions safeguarded?
(3) How is monitoring and reassessment accounted for in the plan?
The questions correspond with the logical triad: what to prepare for, how to respond, and what to monitor?
The four cases considered are as follows: • Dutch Delta Program (DP), planning for adaptation in flood risk management for the Rhine-Meuse delta in the Netherlands.
• Thames estuary 2100 (TE2100) project in the UK, having delivered a plan for flood risk management in the Thames delta.
• PlaNYC 2013. The renewed initiative to adapt New York City after Hurricane Sandy to increasing flood risks (New York City Office of the Mayor ).
• Jakarta Coastal Defence Strategy (JCDS). The project for better protecting against increasing flood risks due to subsidence and sea level rise (JCDS ).
We review and compare the activities on adaptation planning in the four cases on how they tackle the three elements of adaptive planning. Are the chosen approaches fit for purpose? What lessons can be learnt for application in other cases?

APPROACH FOR COMPARING FOUR DELTAS AND COASTAL CITIES
The deltas and coastal cities discussed in this paper share, to some extent, the characteristics that they are highly populated, highly dynamic in terms of economic activity, and share challenges with respect to combined (potential future) effects of sea level rise, river flooding, and soil subsidence. All four cases can be regarded as 'hotspots' where climate and socioeconomic changes coincide, but with different challenges in the short and long term. In addition, in all cases there is an active policy and research community jointly working on meeting these challenges. The information on adaptation planning is drawn from the authors' experiences (all are involved in advising governments on adaptation planning in one of the cases) and their colleagues in working on the adaptation planning.
A general procedure to make an adaptive plan and comply with the aims as described by Sayers et al. () is given by the 'dynamic adaptive policy pathways' framework (Haasnoot et al. ) that combines the approach of adaptive policy making (Kwakkel et al. ) and adaptation pathways (APs) (Haasnoot et al. ). The framework consists of the steps as depicted in Figure 1. In short: (1) analyze the policy agendas to identify the main objectives now and in the future. Identify the external developments that these objectives are most vulnerable for and consequently define scenarios. (2) Assess what amount of change can the system handle: what is the critical level (adaptation tipping point; Kwadijk et al. ()) before the objectives are not met any more? Assess when this occurs by using the scenarios. Besides critical levels that may be a threat to objectives, opportunities may be defined that may help to achieve objectives. Determine possible adaptation actions and by iterative assessment select successful actions (e.g. actions that increase the success of the policy). (3) Once a set of action seems adequate, potential pathways (a sequence of actions) can be constructed and subsequently one or more preferred pathways can be selected as input for a dynamic adaptive plan (4). The aim of this plan is to keep the preferred pathway open as long as possible. For this purpose, contingency actions and triggers for contingency action are specified and after implementation of the plan (5), the variables inducing these triggers are monitored (6).
To compare the cases systematically for the three main research questions a list of questions (Table 1)

FOUR DELTAS AND COASTAL CITIES WITH DIFFERENT CHALLENGES
Thames estuary (TE2100) The Thames estuary is dominated by the London metropolitan area with over 15 million inhabitants. The tidal river Thames serves as a major transport route for the city, one of the UK's major ports. Flood protection standards are high as compared to the rest of the UK with most of the estuary protected to 1/1,000 years. The current flood defense system mainly consists of walls, embankments, flood gates, and the Thames Barrier. The main drivers for adaptation The approximately 600-mile-long coastline and densely populated complex urban environment in combination Step ( Figure 1) Question/indicator Step Step 4 Adaptive plan How are promising strategies determined and translated into a plan? How is the robustness and/or flexibility of the plan safeguarded? What do investment paths look like?
Steps 5 and 6 Implementation and monitoring

Delta Program in the Netherlands
The Rhine-Meuse delta in the Netherlands is a river delta that has originated from marine and fluvial sediments but over the last 1,000 years mainly has been shaped by humans. The digging of canals, drainage systems, creation of polders, the embankment of rivers, and coastal protection has brought prosperity to the delta. In this way the Dutch were able to control water levels and reduce the frequently occurring floods. On the other side, the lack of new sedimentation and extensive drainage has caused land subsidence in substantial parts of the country below sea level (see Figure 2).
With the first delta plan, which started in 1960 and was

Jakarta Coastal Defence Strategy
Jakarta is located on the north coast of Java, Indonesia. The city of Jakarta itself has 9.5 million inhabitants. Together with the daily commuters from the suburban areas, the daytime population is over 12.5 million (JCDS ). Jakarta is rapidly developing. There are many threats to the urban development, including uncontrolled urbanization, heavy traffic problems, water pollution, supply of drinking water, and flood risks (e.g. Steinberg ). In this paper we concentrate on the latter. Flood risks in Jakarta can be characterized by flooding from the sea, from rivers, and from rainfall.
The flood problem in Jakarta is being aggravated by many drivers, both physical and socioeconomic in nature.
In terms of physical changes, rapid land subsidence is a key problem in Jakarta ( contributing factor to past flooding in Jakarta has been the lack of drainage and/or storage capacity in the city's waterways, partly due to them being clogged up by sediments value of assets exposed to flooding is increasing rapidly. The overall aim of JCDS is to protect Jakarta against coastal flooding. To do this, a strategic plan has been developed that 'integrates effective technical solutions to prevent flooding (dikes, retention ponds, and pumps) with additional measures to make the technical solutions sustainable (piped water supply, sewerage and sanitation, and resettlement) and with investment opportunities to make the overall plan financially feasible based on internal cross-subsidies and publicprivate partnership (land reclamation, toll roads, and deep seaport)'. An important aspect of the plan is integration. It therefore also aims to solve drinking water shortages, river pollution, and traffic jams, and to turn Jakarta into an 'attrac-    Figure 4).

Precipitation
Changes in precipitation processes and estimates of associated hydrological consequences are highly uncertain but crucial for flood and drought risk management in the Netherlands. Coupled climate-hydrological models give a large range of possible outcomes, although they mostly agree on an increase of peak discharges under climate change for the Netherlands. Besides SLR, multiple scenarios for precipitation and associated low and peak river discharges have therefore been derived for the DP For Jakarta, only one sea level rise has been projected based on one scenario and no changes in hazard due to possible changes in rainfall intensity have been simulated.
Studies suggest that the impacts of climate change on flood impacts may be relatively small in the coming decades compared to land subsidence. For example, Ward et al.
() developed a model to assess economic assets exposed to a 1/100 year coastal flood event under the current situation, and in the year 2100 as a result of sea level rise and land subsidence. They found that, if land subsidence is not addressed and the rate continues unchecked, and the sea level rises by 59 cm over the 21st century, the value of assets exposed would increase by a factor of 4 between today and 2100. Relative to land subsidence, the impacts of sea level rise are small, yet by no means insignificant, contributing alone to an increase in exposed assets by a factor of We may learn from the above that not necessarily always is a full range of plausible scenarios applied and that scenario use is dependent on the following: 'Perceived uncertainty'. The level of uncertainty perceived in the dominant drivers for change is strongly guiding scenario use. When confronted with severe uncertainty, a larger range of scenarios is used than when confronted with clear and significant observed trends as seen for subsidence in Jakarta.
'Tolerance levels'. The lower the tolerance levels, or the higher the risks involved of assets, people and critical infrastructure to be protected, the larger the need to assess adaptation measures against more high-end climate projections.
'Policy scope'. There are different underlying purposes for using scenarios in a policy process. In the cases we

) or route maps that show the connection between a
short-term decision and longer-term options ( Figure 5).
In the Jakarta case, there is only one such pathway which has been assembled from originally three alternatives (see Figure 6) In the DP in the Netherlands, spatial reservations (Room for the river ) have been made which keep room for river actions (orange branches in Figure 7) open for a long time until design discharges of 18,000 m 3 /s (in the Dutch riskbased approach this represents a discharge that occurs with a return period of 1/1,250 years). Switching between more dike reinforcements and more room for the river, in fact both actions that are part of current strategy, remains possible to cope with long-term projected climate changes.
The TE2100 case can be seen as an example of a well- In the TE2100 and DP, these kinds of measures contribute only partly to the plan, which mainly consists of improving the existing flood safety system of dams, barriers, and dikes. The New York plan promises a wider variety of adaptation actions and more balance between structural, green adaptation, and non-structural measures.

Combining agendas
In the DP there are several short-term decisions defined in the water domain (i.e. redefinition of safety standards, water quality, and shipping issues) that are being connected to the longterm climate change questions. For example, where dikes need to be enforced because of maintenance, the expected increase in water levels due to climate change can be taken into account in the design. Another example is that the planned While other investment agendas may help the implementation of adaptation plans, it is also important to be aware of other agendas or autonomous developments that may hamper and lock out future actions. In the past, spatial developments (see Figure 8) have narrowed down easy options for adaptation. Investments in the past for the Netherlands, but also for example in drainage and dikes in Jakarta, have drawn a lot of economic activity to the low lying parts of the deltas. These autonomous developments may make it difficult to switch to pathways that promote substantial different All plans underpin the importance of monitoring. But because most of the plans are still within the pre-implementation phase monitoring has not been worked out in detail yet. TE2100 has progressed furthest, and a number of key indicators (triggers) have been defined that should be monitored. One of the main indicators is sea level rise that has the potential for early detection of accelerated trends.
The Netherlands has the tradition of evaluating the national water policies from time to time. For this purpose a national monitoring strategy and system is in place. It is expected that the Delta decisions that will result from the DP will require adoption of the future monitoring strategy.
One of the main recommendations for New York is to 'develop a system of indicators and monitoring co-generated by stakeholders and scientists to track data related to climate risks, hazards, and impacts to better inform climate change-related decision-making in New York City'   There is no empirical evidence found yet within the cases on reassessment based on monitoring.

LESSONS LEARNT
Adaptation planning in four cases around the globe concerning flood risk management in deltas and coastal cities has been compared on three main supposed characteristics of adaptive planning: to prepare for a wide range of plausible future scenarios (climate, subsidence, and socioeconomic), to respond to uncertain change with a robust and flexible set of actions, and to monitor critical changes to be able to reassess the plan accordingly. All four cases follow purposely an adaptive planning approach to arrive at an adaptation strategy, but differences can be observed in the implementation. These differences can be related to the context of the The cases of TE2100 and DP highlight how short-term decisions are explicitly coupled with long-term options using APs or route maps with clearly marked thresholds defining when to decide to switch from one action to another, this ensures maximum flexibility.
The Jakarta case provides the best example on how shortterm decisions are part of a phased implementation of a 'multi-objective' plan. The city's demand for spatial development of infrastructure, and new areas for housing and business creates the opportunity for financing the combined large investments in flood defenses, roads, and polder areas in this way reducing the flood risk. However, the long-term possible consequences of climate change remain underexposed. In general, developing countries where poverty and short-term vulnerabilities dominate over long-term concerns, the long-term planning approaches may need to be tailored to be effective (Ranger & Garbett-Shiels ). In these countries, long-term planning is much less practiced, because as the Jakarta case shows, other (more urgent) problems exist. The challenge is to design actions that are also able to cope with potential future conditions (robust actions or design actions that leave room for adaptation if needed) and seize opportunities once they arise. Therefore, it is even more important to link (potential) future actions to current problems, for example by searching for win-win options.
The third strategy encountered is increasing resilience (and in this way robustness), as is best illustrated by the plaNYC case, which is not only directed at designing adaptation actions for a certain amount of climate change but also to make the city stronger to protect against, cope with, and recover from uncertain future flood hazards. On the third research question, 'how is monitoring and reassessment included in the plans?', the main conclusion is that the importance is recognized, that the main climate drivers for change are being considered in monitoring plans, other key triggers are being defined and, since not all relevant variables are suitable for early trend detection, progress in science and climate projections should also be monitored. However, there is little experience yet to be collected, for example on how monitoring can be used to implement or improve strategies.