Exploring the limits and gaps of flood adaptation

Flood adaptation measures, such as levees, flood-proofing structures, nature-based solutions, and flood insurance, are essential to cope with the growing flood risk caused by climate change and urban development in flood-prone areas. However, many communities in flood zones are inadequately protected because the implementation of adaptation measures is hindered by various constraints, including cost, limitations in institutional capacity, and societal inertia. When adaptation efforts fall short relative to the desired level due to a combination of constraints, it results in an ‘adaptation gap’ and eventually leads to ‘adaptation limits’—a point in time where additional adaptation is no longer feasible and the risk becomes ‘intolerable.’ While the emerging field of socio-hydrology has made progress in studying the adaptive feedbacks from society to environmental changes, a quantitative assessment of adaptation limits and gaps has not yet been conducted.

In this paper, we introduce a novel, risk-based framework to quantify how changes in risk and adaptation constraints might result in the spatial-temporal dynamics of adaptation gaps and, ultimately, adaptation limits. With hundreds of millions of people living in flood-prone areas, understanding how these constraints affect adaptation gaps and potential limits—and where and when these limits are reached—is crucial for quantitative risk assessments. This information is particularly helpful for efforts to build resilience in the most vulnerable communities, some of which may have already reached such limits. We discuss five main categories of constraints that limit adaptation efforts, ranging from technical constraints that prevent the government from implementing levees to socio-economic constraints (such as age and income) that limit flood adaptation by households.

We argue that, without overcoming these constraints, adaptation gaps will widen under climate change, exposing increasing populations to heightened flood risk. This may then require more radical actions including relocation, as risks become intolerable. We argue that quantitative flood risk assessments must consider constraints and adaptation gaps systematically, especially where they may lead to flood adaptation limits. Without assessing these dynamic relationships, flood managers may overestimate the efficacy of flood adaptation measures and underestimate the unequal distribution of flood risks.

Reference: Aerts, Jeroen C.J.H., Paul Bates, Wouter J. Botzen, Jens de Bruijn, Jim Hall, Bart van den Hurk, Heidi Kreibich, Bruno Merz, Sanne Muis, Jaroslav Mysiak, Eric Tate, and Frans Berkhout (2024) Exploring flood adaptation limits and gaps. Nature Water, doi-org.vu-nl.idm.oclc.org/10.1038/s44221-024-00274-x