Uncertainty and Bias in Global to Regional Scale Assessments of Current and Future Coastal Flood Risk

This study provides a literature-based comparative assessment of uncertainties and biases in global to world-regional scale assessments of current and future coastal flood risks, considering mean and extreme sea-level hazards, the propagation of these into the floodplain, people and coastal assets exposed, and their vulnerability. Globally, by far the largest bias is introduced by not considering human adaptation, which can lead to an overestimation of coastal flood risk in 2100 by up to factor 1300. But even when considering adaptation, uncertainties in how coastal societies will adapt to sea-level rise dominate with a factor of up to 27 all other uncertainties. Other large uncertainties that have been quantified globally are associated with socio-economic development (factors 2.3–5.8), digital elevation data (factors 1.2–3.8), ice sheet models (factor 1.6–3.8) and greenhouse gas emissions (factors 1.6–2.1). Local uncertainties that stand out but have not been quantified globally, relate to depth-damage functions, defense failure mechanisms, surge and wave heights in areas affected by tropical cyclones (in particular for large return periods), as well as nearshore interactions between mean sea-levels, storm surges, tides and waves. Advancing the state-of-the-art requires analyzing and reporting more comprehensively on underlying uncertainties, including those in data, methods and adaptation scenarios. Epistemic uncertainties in digital elevation, coastal protection levels and depth-damage functions would be best reduced through open community-based efforts, in which many scholars work together in collecting and validating these data.

Hinkel, J., L. Feyen, M. Hemer, G. Le Cozannet, D. Lincke, M. Marcos, L. Mentaschi et al. Uncertainty and bias in global to regional scale assessments of current and future coastal flood risk. Earth’s Future: e2020EF001882. (2021) https://doi.org/10.1029/2020EF001882

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Risks on global financial stability induced by climate change: the case of flood risks

There is increasing concern among financial regulators that changes in the distribution and frequency of extreme weather events induced by climate change could pose a threat to global financial stability. We assess this risk, for the case of floods, by developing a simple model of the propagation of climate-induced shocks through financial networks. We show that the magnitude of global risks is determined by the interplay between the exposure of countries to climate-related natural hazards and their financial leverage. Climate change induces a shift in the distribution of impacts towards high-income countries and thus larger amplification of impacts as the financial sectors of high-income countries are more leveraged. Conversely, high-income countries are more exposed to financial shocks. In high-end climate scenarios, this could lead to the emergence of systemic risk as total impacts become commensurate with the capital of the banking sectors of countries that are hubs of the global financial network. Adaptation policy, or the lack thereof, appears to be one of the key risk drivers as it determines the future exposure of high-income countries. This implies in particular that the avoided costs in terms of financial stability should be weighted in as benefits of adaptation policy.

Mandel, A., Tiggeloven, T., Lincke, D. et al. Risks on global financial stability induced by climate change: the case of flood risks. Climatic Change 166, 4 (2021). https://doi.org/10.1007/s10584-021-03092-2

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Coastal protection can significantly reduce migration from sea-level rise

Protecting densely populated coastal areas, such as river deltas or megacities, from sea-level rise with dikes and seawalls will likely limit land loss and migration of people away from the coasts. But these protections are overlooked in most migration estimates. A new study predicts coastal protection could limit migration to 17 to 72 million people during the 21st century—less than half of some previous estimates.

The study, published in Earth’s Future, AGU’s journal for interdisciplinary research on the past, present and future of our planet and its inhabitants, is the first to look at the effects of coastal protection on migration rates on a global scale. The analysis takes into account a wide range of climate change and economic scenarios.

The authors find that, from a purely economic point of view, it makes sense to protect about 3% of the global coastline—mainly around densely populated cities and floodplains. However, for people living on less populated coastlines in poorer communities with fewer assets to protect, retreating would be a more affordable option for local governments than investing in protection.

“Nobody will give up New York City or the Netherlands, at least not in the 21st century, so we wanted to take this into account to get a more realistic picture of coastal migration due to sea-level rise,” said Daniel Lincke, a coastal researcher at the Global Climate Forum, an independent research institute focused on climate change research.

People have kept out the sea with dikes and other barriers for hundreds of years. The Netherlands, for example, began building dikes at least as far back as the 1200s. As sea levels continue to rise due to climate change, many countries will likely construct seawalls and other defenses to protect densely populated areas.

From a technical standpoint, Lincke expects that all coastal megacities potentially could be protected, at least up to the 2 meters (6.56 feet) of sea-level rise predicted by 2100 under the worst climate change scenarios. But building and maintaining coastal protection infrastructure comes at a high cost that could add up to several trillions (US$) globally through the 21st century.

Most studies have not considered coastal protection in their estimates of the impacts of sea-level rise, Lincke said, potentially leading scientists to overestimate the number of potential migrants from coastal areas.

“There have been global studies of cost-benefits of flood protection, and global studies on migration, but in this paper, they nicely combined them,” said Hans de Moel, a natural hazard risk researcher at Vrije Universiteit Amsterdam who was not involved in the study. “It’s important because you don’t want to look at adaptation measures in isolation.”

Lincke and his co-author Jochen Hinkel of the Global Climate Forum developed a model that splits the global coastline into about 12,000 pieces based on local elevation, population and socioeconomic data. For each piece of coastline, they used the model to estimate the local costs of constructing and maintaining protection, retreating from the land and losing its assets or repairing flood damage. They considered 250 potential future scenarios with differing amounts of sea-level rise and global wealth. Then they estimated the number of migrants, assuming that local governments would make protection decisions based purely on this cost-benefit analysis.

The researchers emphasize that their analysis focuses on economic factors, but that social and political factors also play powerful roles in how individuals and societies react to the threat of rising sea-levels.

For 3.4% of the world’s coastline, all of the scenarios agreed that coastal protection was a less costly option for the country than migration or repairing flood damage. These regions include coastal urban areas in China, Japan and Europe, and cities in the U.S., Australia, Indonesia and the Nile delta.

“You cannot protect everywhere—that will not be possible,” Lincke said. The analysis also takes into account the wealth level of each country and the local cost of constructing dikes. For regions with fewer people or less valuable property along the coasts, retreat and the likely migration of coastal residents is predicted to cost a country less than protection, which may guide decision-making. As a result, “it is very probable that the locations where people have to retreat are mainly in poor and developing countries,” Lincke said.

Densely populated countries in South Asia and Southeast Asia are predicted to have the highest numbers of migrants. Small island states, such as the Pitcairn Islands, the Marshall Islands and Kiribati, will also suffer high relative migration rates, with more than half the population of some islands likely being forced to move.

Depending on the scenario, sea-level rise is predicted to claim about 60,000 to 415,000 square kilometers (about 23,000 to 160,000 square miles) worldwide. The U.S., Russia and Canada are expected to lose the most land, as they have long and mainly sparsely populated coastlines.

de Moel suggests that the next step would be to look at models of how people decide when to migrate in the face of sea-level rise. These would include factors like a person’s risk perception, sense of place and the effects of previous extreme flooding events, like Hurricane Katrina in the U.S. and Cyclone Xynthia in France. He said that these events can trigger people to migrate well before their land becomes inundated. His group at Vrije Universiteit Amsterdam is working on such a model. “This is a very nice foundational piece on which we can move forward.”

Earth’s Future is an open access journal. The paper can be accessed under https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020EF001965

New GCF Working Paper (02/21): The Decision Theatre Triangle for societal challenges

The Decision Theatre Triangle for societal challenges

To support discussions about the challenge of a sustainable mobility transition between researchers and stakeholders, such as practice experts, decision makers, and citizens, we have developed and tested an agent-based model and a mobile Decision Theatre set-up. Due to the combination of three elements: a) mathematical modelling and simulation, b) socio-ecological, including socio-economic, data and understanding, and c) a dialogue format based on the former two elements for bringing together researchers and stakeholders — we refer to the method as the Decision Theatre Triangle. This paper presents insights gained with the sustainable mobility case and, based on these, outlines research needs for turning this method into an easy-to-set-up instrument of science communication, decision support, and co-production of research for societal challenges more generally.

Access the paper HERE or through the link in the title above.

New publication: The European Green Deal – More Than Climate Neutrality

The European Green Deal – More Than Climate Neutrality

The European Green Deal aims at climate neutrality for Europe by 2050, implying a signifi cant acceleration of emission reductions. To gain the necessary support, it needs to reduce regional and social inequalities in Europe. We present objectives in terms of jobs, growth and price stability to complement the emission reduction targets and sketch a proof-of-concept investment profi le for reaching these goals. Substantial additional annual public investments, of about 1.8% of pre-COVID-19 GDP, are proposed for the next decade. Their allocation includes retrofi tting the European building stock, consciously fostering a renewal of the European innovation system as well as complementary measures in the fields of education and health. The scenario outlined in this article is meant as an input to the urgently needed discussion on how the European Green Deal can shift the EU economy to a new development path that realises a carbon-neutral Europe by 2050 while strengthening European cohesion.

Jaeger, C., J. Mielke, F. Schuetze, J. Teitge, S. Wolf. 2021. The European Green Deal – More Than Climate Neutrality. Intereconomics. Volume 56, March/April 2021, Number 2. DOI: 10.1007/s10272-021-0963-z.


Integrating new sea‐level scenarios into coastal risk and adaptation assessments: An ongoing process

The release of new and updated sea‐level rise (SLR) information, such as from the Intergovernmental Panel on Climate Change (IPCC) Assessment Reports, needs to be better anticipated in coastal risk and adaptation assessments. This requires risk and adaptation assessments to be regularly reviewed and updated as needed, reflecting the new information but retaining useful information from earlier assessments. In this paper, updated guidance on the types of SLR information available is presented, including for sea‐level extremes. An intercomparison of the evolution of the headline projected ranges across all the IPCC reports show an increase from the fourth and fifth assessments to the most recent “Special Report on the Ocean and Cryosphere in a Changing Climate” assessment. IPCC reports have begun to highlight the importance of potential high‐end sea‐level response, mainly reflecting uncertainties in the Greenland/Antarctic ice sheet components, and how this might be considered in scenarios. The methods that are developed here are practical and consider coastal risk assessment, adaptation planning, and long‐term decision‐making to be an ongoing process and ensure that despite the large uncertainties, pragmatic adaptation decisions can be made. It is concluded that new sea‐level information should not be seen as an automatic reason for abandoning existing assessments, but as an opportunity to review (i) the assessment’s robustness in the light of new science and (ii) the utility of proactive adaptation and planning strategies, especially over the more uncertain longer term.

Nicholls, R.J., Hanson, S.E., Lowe, J.A., Slangen, A., Wahl, T., Hinkel, J. and Long, A.J., 2020. Integrating new sea-level scenarios into coastal risk and adaptation assessments: An on-going process. WIREs Climate Change. https://doi.org/10.1002/wcc.706

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Unravelling the Importance of Uncertainties in Global-Scale Coastal Flood Risk Assessments under Sea Level Rise

Global scale assessments of coastal flood damage and adaptation costs under 21st century sea-level rise are associated with a wide range of uncertainties, including those in future projections of socioeconomic development (shared socioeconomic pathways (SSP) scenarios), of greenhouse gas concentrations (RCP scenarios), and of sea-level rise at regional scale (RSLR), as well as structural uncertainties related to the modelling of extreme sea levels, data on exposed population and assets, and the costs of flood damages, etc. This raises the following questions: which sources of uncertainty need to be considered in such assessments and what is the relative importance of each source of uncertainty in the final results? Using the coastal flood module of the Dynamic Interactive Vulnerability Assessment modelling framework, we extensively explore the impact of scenario, data and model uncertainties in a global manner, i.e., by considering a large number (>2000) of simulation results. The influence of the uncertainties on the two risk metrics of expected annual damage (EAD), and adaptation costs (AC) related to coastal protection is assessed at global scale by combining variance-based sensitivity indices with a regression-based machine learning technique. On this basis, we show that the research priorities in terms of future data/knowledge acquisition to reduce uncertainty on EAD and ACdiffer depending on the considered time horizon. In the short term (before 2040), EAD uncertainty could be significantly decreased by 25 and 75% if the uncertainty of the translation of physical damage into costs and of the modelling of extreme sea levels could respectively be reduced. For AC, it is RSLR that primarily drives short-term uncertainty (with a contribution ~50%). In the longer term (>2050), uncertainty in EAD could be largely reduced by 75% if the SSP scenario could be unambiguously identified. For AC, it is the RCP selection that helps reducing uncertainty (up to 90% by the end of the century). Altogether, the uncertainty in future human activities (SSP and RCP) are the dominant source of the uncertainty in future coastal flood risk.

The online version of the paper is accessible here

Rohmer, J.; Lincke, D.; Hinkel, J.; Le Cozannet, G.; Lambert, E.; Vafeidis, A.T. Unravelling the Importance of Uncertainties in Global-Scale Coastal Flood Risk Assessments under Sea Level Rise. Water 2021, 13, 774. https://doi.org/10.3390/w13060774

Sea level rise up to four times global average for coastal communities

Coastal populations are experiencing relative sea-level rise up to four times faster than the global average – according to new research from an international research team that includes Global Climate Forum.

A new study published today in Nature Climate Change is the first to analyse global sea-level rise combined with measurements of sinking land. Climate-induced sea-level rise is a known threat to coastal populations, but the role of land subsidence in influencing relative sea level is less recognised. Recently, sea-level rise around the world’s coasts, including subsidence, averages 2.6 mm/yr. However, coastal residents on average experience sea-level rise four times faster at 7.8-9.9 mm/yr, reflecting that people preferentially live in subsiding areas, especially on deltas and in cities on deltas. Hence, contemporary risks of relative sea-level rise are much worse than previously recognised. Urgent and feasible action is needed to control and mitigate human-induced subsidence in populated areas.

The research team assessed four components of relative sea-level change – climate induced sea-level change, the effects of glacier weight removal causing land uplift or sinking, estimates of river delta subsidence and subsidence in cities. Sea-level measurements were taken from satellite data. The team then weighted their results by population to show their importance to people. The overall analysis used the Dynamic Interactive Vulnerability Assessment (DIVA) model which is designed for understanding coastal management needs.

They found that high rates of relative sea-level rise are most urgent in South, South East and East Asia as the area has many subsiding deltas and coastal flood plains, growing coastal megacities and more than 70 per cent of the world’s coastal population. They also found that over the 20th Century, the city of Tokyo experienced net subsidence of 4m, while Shanghai, Bangkok, New Orleans, and Jakarta, have experienced between 2m and 3m subsidence. In Tokyo, Shanghai and Bangkok the subsidence has been stopped or greatly reduced by reduced groundwater extraction, while in other cities there has been little direct response to reduce subsidence.

Nicholls, R.J., Lincke, D., Hinkel, J., Brown, S. Vafeidis, A.T., Meyssignac, B., Hanson, S.E., Merkens, J.-L., Fang, J. (2021). A global analysis of subsidence, relative sea-level change and coastal flood exposure. Nature Climate Change. https://doi.org/10.1038/s41558-021-00993-z

New working paper: The European Green Deal, More than climate neutrality

The European Green Deal aims at climate neutrality of Europe by 2050, implying a significant acceleration of emission reductions. To gain the necessary support, at the same time it needs to reduce regional and social inequalities in Europe. We propose objectives in terms of jobs, growth, and price stability to complement the emission reduction targets and present a proof-of-concept investment profile for reaching these. Substantial additional public investments, of about 1.8% of last year’s GDP annually, are proposed for the next decade. Their allocation includes retrofitting the European building stock, consciously fostering a renewal of the European innovation system, and complementary measures such as education and health. The scenario thus outlined is meant as an input to the urgently needed discussion about how the European Green Deal can shift the EU economy to a new development path that realizes a carbon neutral Europe by 2050 while strengthening European cohesion much earlier.
This paper presents a new and substantially updated version of the previous GCF Working Paper no 1/2020.
Access the paper HERE or through the link in the title.


What drives relocation policies in the Maldives?

The predominant responses to rising sea levels are in situ adaptations. However, increasing rates of sea-level rise will render ex situ adaptations—in the form of relocations—inevitable in some low-lying coastal zones. Particularly small island states like the Maldives face this significant adaptation challenge. Here, government action is necessary to move vulnerable communities out of flood-prone areas. Yet, little empirical knowledge exists about the governance of relocations. While the literature often highlights risks and benefits of relocations, it remains unclear how governments organized relocations and what drove relocation policy. Therefore, we examined Maldivian relocation policies from 1968 to 2018 to explain government support of relocations. For this, we used a qualitative research design and extended the multiple streams approach with the theoretical lens of historical institutionalism. To gather data, we conducted semi-structured interviews (n = 23) with relocation policy experts and locals affected by relocations. Interview data was complemented with a desk review of relevant laws, historical records, and policy documents. We find 29 completed and 25 failed cases of relocations in the 50-year period. Key drivers of relocation policies are focusing events, socioeconomic development, and institutionalized island autonomy. We find that relocations were predominantly initiated as means to facilitate economic development, not as a response to rising seas or coastal risk. With current rapid economic development and strengthened democratic institutions, relocations are not considered as a policy option anymore. We conclude that implementing relocations proactively will face significant barriers in the future, which highlights the urgency of successful in situ adaptations in the Maldives.

The online version of the paper is accessible here

Gussmann, G., Hinkel, J. (2020). What drives relocation policies in the Maldives?. Climatic Change (2020). https://doi.org/10.1016/j.envsci.2020.09.028