Urban flooding - Risks, technologies and community response

Climate overshoot, insurance and financial-protection stress: a global subnational analysis
Climate overshoot can create a temporary period of heightened heat exposure before end-of-century conditions partially scales down. Where that peak occurs against weak financial-protection capacity matters for adaptation finance and disaster-risk finance, yet global evidence is largely national or based on composite indices that blur hazard and capacity.

We reconstruct model-specific peak-period heat exposure from 14 CMIP6 SSP5-3.4-OS models and cross-classify it with a five-component national financial-protection capacity measure across 2,280 first-order administrative regions (ADM1) in 128 countries, representing 6.83 billion people using harmonized 2020 population. Under a reference definition, the highest 20% of regional peak-period heat exposure and the lowest 25% of national capacity, 223 regions in 28 countries, containing 643.7 million present day residents, are classified as high exposure/low capacity. Across 448 prespecified

specifications, 117 regions in 16 countries containing 297.1 million people are selected in at least 90% of cases. Bangladesh contributes the largest population to this robust core (84.0 million), followed by Sudan, Ghana, Niger, Mali and Burkina Faso, with additional concentrations in Cambodia and other African and Central American countries. Each screening dimension also shows independent empirical relevance: capacity is positively associated with insured catastrophe-loss share across 29 European countries, while peak-period heat exposure is positively associated with three

observed U.S. insurance-market stress outcomes. The overshoot signal is geographically widespread: in 99.7% of ADM1 regions, the ensemble-median peak-period temperature exceeds the end-century value, and at least 10 of 14 models agree on this direction in 95.0% of regions. Models agree much less, however, on which regions experience the largest peak-to- end decline (median pairwise spatial rank correlation ρ = 0.10). Overshoot therefore provides a robust basis for identifying

the period of heightened exposure, but not for finely ranking regions by the magnitude of subsequent temperature reversal. The framework identifies where pre-arranged finance, risk-pooling and capacity-building attention may be most urgent before peak climate stress arrives; it is not a forecast of insurer withdrawal or future institutional performance

Floods Are Climate-Driven; Humanitarian Disasters Are the Result of Human Choices
Autores : Hélio Vasco Nganhane; Alexandre Oliveira Tavares; Pedro Pintos Santos and Gustavo Dge-Dge

Floods are among the most destructive climate-related hazards across Mozambique and Southern Africa. While flood events are climate-driven, their transformation into humanitarian disasters is largely determined by human choices. This study presents a multi-decadal assessment (1977–2026) to disentangle the relative roles of climate forcing and anthropogenic factors in shaping flood disaster risk. An integrated Hazard–Exposure–Vulnerability framework combines hydroclimatic records, satellite-derived flood extent, land-use change, demographic trends, and governance indicators. Results show that although extreme rainfall and river discharge have become more variable under climate change, humanitarian impacts have increased far more rapidly than the physical hazard itself. Rapid settlement in floodplains, unplanned urbanization, ecosystem degradation, inadequate land-use planning, weak governance, and limited resilient infrastructure have amplified exposure and vulnerability across the region. The transboundary nature of Southern African river basins further complicates flood risk management. The findings demonstrate that climate change increases flood hazard, but the scale of humanitarian disasters is primarily determined by societal decisions regarding territorial planning, environmental management, governance, and disaster risk reduction. Reducing future losses therefore requires integrating climate adaptation with risk-informed development, ecosystem protection, resilient infrastructure, and people-centred early warning systems. The study provides policy-relevant evidence for COP31 by highlighting that resilience depends not only on addressing climate change but also on transforming the human conditions that convert natural hazards into humanitarian disasters.

A review study on community-based flood adaptation in informal settlements in the Global South
Johannes Bhanye
African Climate and Development Initiative (ACDI), University of Cape Town, Cape Town, South Africa

Urban flooding is an escalating climate hazard in Global South cities, with disproportionate impacts on informal settlements characterised by insecure tenure, inadequate infrastructure and high social vulnerability. This published rapid review uses the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology to synthesise 15 peer-reviewed studies on the scope, effectiveness and challenges of community-based adaptation (CBA) to flooding in informal settlements. The evidence identifies complementary structural measures, including reblocking, drainage improvements and raised latrines, and non-structural measures such as early-warning systems, savings groups and community mapping. Participatory GIS, citizen science and mobile flood communication expand communities’ capacity to produce risk knowledge and coordinate action, while livelihood diversification, gender-responsive practices and Indigenous and local knowledge strengthen adaptive capacity. Effective CBA is commonly supported by partnerships among communities, NGOs and local governments; however, limited finance, weak urban governance, insecure tenure and legal exclusion restrict sustainability and scaling. The review shows that CBA can make flood adaptation more locally grounded, inclusive and responsive to lived realities, but cannot substitute for accountable public institutions and equitable investment. It recommends integrating CBA into formal disaster-risk reduction and climate-resilient urban planning, sustaining community participation, directing resources to marginalised settlements and strengthening mechanisms for evaluating long-term impacts. These findings provide actionable evidence for advancing just, participatory and scalable urban flood resilience.

Towards Water Infrastructure in the Risk Equation: Geospatial Flood-Risk Evidence for Resilient Drainage and Irrigation in Coastal States
Dr. Vairaj Arjune, National Adaptation Officer, Global Green Growth Institute.

Floods are not new to the developing world, yet they continue to overwhelm the water infrastructure (drainage and irrigation) on which low-lying coastal and island states depend. The study area is Guyana, where a narrow coastal plain sustains over 90% of the population and nearly all agricultural production behind a colonial-era, gravity-fed, tide-dependent system of canals, sluices, and pumps. Flooding accounts for roughly 98% of the country's average annual loss to infrastructure, estimated at nearly USD 89.7 million; global modelling suggests as much as 99% could be avoided through resilience-based strategies.

The study set out to build an evidence base for embedding resilience into national drainage and irrigation planning. It draws together a structured situational analysis, comprising a stakeholder workshop, thirteen semi-structured expert interviews, and a multi-agency focus group across the coastal regions, with an integrated geospatial flood-risk assessment. Following the IPCC SREX framing, eleven normalised indicators spanning Hazard, Exposure, and Vulnerability were combined from national inventories and open global datasets to map risk at national, infrastructure-point, and individual-farm scales.

What distinguishes the analysis is its treatment of the drainage and irrigation network itself as a variable within the risk equation, an element prevailing global infrastructure risk models tend to overlook. The results reveal not only where risk is greatest, but where existing infrastructure already reduces it and where investment would yield the largest marginal gain. The study thus converts diffuse climate concern into spatially explicit, financeable priorities. Grounded in globally available data, the method is low-cost and replicable, offering a transferable template for directing disaster-resilience finance across similarly exposed developing and small island states.