“I want to see economically optimal coastal adaptation options both today and, in the future, as well as the expected investments in coastal adaptation and the potential costs of flood damages.”

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1. What is a CoCliCo User Story?

User Stories are ready-made map datasets in the CoCliCo platform. They combine different types of important information to show scenarios for coastal risk resulting from sea-level rise,  floods and / or erosion. These layers make complex analyses easier and help users to quickly get a sense of coastal risks. 

User research showed that policymakers need clear, actionable data for flood directives, while urban planners want tools to assess local risks, and where infrastructure managers focus on long-term resilience planning. These insights helped shape User Stories to provide accessible, scenario-driven visualizations for diverse decision-making needs. There are six User Stories:

1. Sea Level Rise Projections
2. Inundation Distribution During a Flood Event
3. Building Exposure
4. Projections of Exposed People
5. Damage Costs of Exposed Infrastructures
6. Adaptation Based on Cost-Benefit Analysis

In this e-guideline, we walk you through the Adaptation Based on Cost-benefit Analysis User Story.

2. Introduction to the Adaptation Based on Cost-benefit Analysis User Story

The Adaptation Based on Cost-Benefit Analysis User Story in the CoCliCo platform helps identify the most cost-effective ways to manage coastal flood risks under different climate scenarios. It evaluates three key adaptation strategies:

• Protection – Building coastal defences like seawalls or restoring dune fields.
• Retreat – Relocating people and assets away from flood zones.
• Accommodation – Flood-proofing buildings to withstand extreme events.

The platform provides country-level insights on the best mix of these strategies, with more detailed local assessments available through the workbench. This helps policymakers and planners make informed, cost-effective adaptation decisions.

3. Step-by-Step Platform Usage

1. Access the CoCliCo Platform:
   1. On the left-hand menu bar, navigate to the “Risk & Adaptation” category, then “Cost-benefit analysis of coastal adaptation” under “User Stories”. 
2. Select a Scenario:
   1. Choose a climate scenario (e.g., SSP1-2.6, SSP2-4.5, etc.), time horizon and adaptation strategy.
3. Analyze Visualizations:
   1. Use interactive tools to zoom into regions and access localized insights.
   2. Use the “Add to Dashboard” feature to retain charts and graphs for further comparison and analysis
   3. Toggle on other layers, such as “natural hazards” and “exposure & vulnerability,” for more context on the impacts and risks faced by that area. For simpler comparisons, make sure you add your charts and graphs to your dashboard to compare across time and geographies and observe various layers and user stories of that area. 
4. Further Analysis:
   1. Export maps or raw datasets for further analysis in the Workbench or other GIS tools​​.
   2. Assess local projections with vertical land motion (VLM) using our coastal hazard assessment.

4. Target Users & Intended Use

Target Users:

• Policymakers implementing national and EU flood directives.
• Urban planners and city authorities in coastal areas.
• Researchers and consultants assessing the economics of coastal impacts.

Intended Use:
This User Story provides an overview of the most cost-efficient adaptation options at the country level, helping with broad decision-making. For more detailed insights, local coastal floodplain analyses available in the workbench can support more specific, local decisions.

The analysis aims to kickstart discussions about coastal adaptation strategies, identify areas where doing nothing would be costly, and offer initial suggestions for adaptation options and their timing. However, a more detailed local assessment should follow since the continental-scale analysis here doesn’t include the finer details that could affect the suitability of adaptation options for specific locations.

Key Benefits:

• Enables informed adaptation planning at all scales (national to municipal).
• Gives justification for coastal adaptation investments and strategic land-use decisions.

5. Example of use 

“National policymakers identified that significant funding would be required to address coastal flood risks in various regions. They allocated funding for coastal adaptation, encouraging local authorities to conduct their own research. This approach allowed local governments to assess specific risks and develop tailored solutions, ensuring more effective, region-specific adaptation strategies.”

6. Data, Methods, and Model Overview

Data Sources:

Regional median sea-level projections, excepted vertical land motions (VLMs), costs for adaptation investments and current protection levels in Europe are from other deliverbales/workpackages in CoCliCo. Extreme return periods are from COAST-RP (Dullaart e al. 2021). We model hypsometric profiles for each coastal floodplain based on the Copernicus digital elevation model (DEM) and population data from the Global Human Settlement Layer.

Methods:

The cost-benefit optimisation integrates several components:

• A hazard component to model extreme sea level
• An exposure component to assess population and assets at risk
• A vulnerability component to assess the susceptibility of assets to hazards
• An adaptation state space to outline potential adaptation pathways
• Cost functions to estimate the costs associated with adaptation actions

The multi-stage cost-benefit optimisation is conducted for each of the 41,327 coastal floodplains individually. We consider a time horizon from 2020 to 2150 with 10-year time steps, a discount rate of 3% and three greenhouse gas emission scenarios: low emissions (SSP1-2.6), high emissions (SSP2-4.5) and very high emissions (SSP5-8.5).

Model Outputs:

• For each coastal floodplain, the model determines the economically optimal adaptation pathway, which is a sequence of adaptation options over time. These adaptation pathways can be further explored through the workbench.
• The web viewer illustrates the proportion of the coastline where each adaptation option is economically optimal by 2150 for each country, based on the economically optimal coastal adaptation pathways for all 41,327 floodplains.

Limitations

This cost-benefit model uses broad data to manage computational limits, which means it doesn’t include detailed information about properties, land use, or infrastructure. As a result, the model may be less accurate for specific floodplains. For example, it might suggest retreat as the best adaptation option for an area with a nuclear power plant, but this could present major challenges that the model doesn’t account for.

The model also only considers the median sea-level rise (SLR), leaving out high-end SLR scenarios. A sensitivity analysis showed that uncertainties in factors like the discount rate, protection and retreat costs, and protection levels have a bigger impact on the choice of adaptation options, the timing of actions, and total costs than the climate change scenarios themselves.

7. Further Analysis 

Technical users can use the Workbench to perform detailed, localised analyses by adjusting variables like flood risks, cost factors, and adaptation options. This allows for tailored assessments of the most cost-effective strategies and the timing of actions at the local scale.

Users can explore different sea-level rise scenarios, test adaptation measures, and incorporate local data such as infrastructure details to refine their analysis. The Workbench enables deeper insights, helping inform more precise local adaptation strategies.