Urban flood protection strategies have historically relied on structural defenses such as levees, dams, and embankments to shield cities from rising water levels during extreme weather events. In recent years, as urban centers across the globe grapple with increasing flood hazards intensified by climate change and rapid urbanization, many have turned towards partial flood defense systems—protective structures that do not envelop an entire city but instead safeguard select, critical areas. A groundbreaking study focusing on Surat, India, a rapidly growing metropolis prone to flooding, reveals not only the benefits of such partial levee installations but also their unintended socio-spatial consequences, including the amplification of inequality and the reshaping of flood risk dynamics across time.
The research applied a state-of-the-art hydrodynamic modeling technique simulating a 100-year return period flood event, a statistical estimate of a once-in-a-century extreme flood discharge. Utilizing this model, the study meticulously mapped floodwater propagation throughout the urban and suburban landscape of Surat, paying close attention to how a partial levee system modifies the volume, depth, and timing of flooding in different neighborhoods. The choice of a 100-year flood event provides a stringent test of levee effectiveness, highlighting how cities might fare during severe but plausible flood catastrophes exacerbated by changing climate patterns.
One fundamental finding from this research underscores that the introduction of partial levee coverage yields substantial reductions in economic damages across core urban wards, which represent the city’s densely populated and economically vital areas. In financial terms, the study estimates that levee implementation diminishes aggregate flood losses by approximately ₹31.24 billion (around US$380 million) in the central urban wards. Simultaneously, suburban neighborhoods, often less protected and characterised by different land-use patterns, also benefit from damage reductions, albeit to a smaller extent estimated at ₹10.34 billion (US$125 million). These figures demonstrate that even partial flood defenses can generate significant cost-saving benefits by limiting the inundation and destruction of critical urban infrastructure and properties.
However, the research team faced an alarming twist: the benefits accrued by certain geographic pockets of the city come at the cost of amplified exposure and damage inequality in the broader urban fabric. By harnessing social and demographic datasets alongside flooding data, the study considered how flood damage and exposure—defined as the population or assets endangered by flooding—vary across different communities. The results revealed a sharp increase in inequality metrics, particularly the Gini index, a widely used measure of inequality. Here, the Gini index for flood damage escalated by about 20%, from 0.55 to 0.66, signaling that losses became more unevenly distributed post-levee construction. Similarly, flood exposure inequality leapt by roughly 26%, rising from 0.31 to 0.39, indicating that while some populations experienced reduced risk, others confronted disproportionately higher hazards.
What causes this distorted risk landscape? The study introduces novel concepts such as “flood stripes” and a “protection-induced time shift” to explain the spatial and temporal modifications of the flooding regime imposed by partial levees. The flood stripes represent newly drawn spatial patterns of flood intensity and timing across the city, illuminating how waters no longer rise uniformly after structural defenses are in place. Instead, these defenses provide effective protection to near-river wards, allowing them to remain flood-free for significantly longer periods—up to 12 hours—during an extreme flood event. This temporal buffer can translate to critical response and evacuation advantages that preserve lives and assets in these neighborhoods.
Conversely, the tradeoff for these near-river wards is a more precarious reality downstream and in peripheral urban areas, where some locations start to experience flooding up to 7 hours earlier than before the levees. This acceleration of flood exposure shifts the risk frontlines and forces vulnerable populations in these areas to confront an altered hazard timeline, often without the infrastructure or resources to adapt effectively. These downstream communities suffer increasing flood depths and durations as floodwaters diverted or delayed elsewhere eventually inundate them. The implication is clear: flood defenses are not uniform risk mitigators but risk redistributors, sculpting temporal and spatial contours of vulnerability in ways that can exacerbate existing socio-economic divides.
The phenomenon presents a challenge for urban planners and policymakers aiming to balance efficient flood risk reduction with social equity. While partial levee systems may accomplish the laudable goal of preserving economic hubs and dense urban sectors, they inadvertently concentrate risk on historically peripheral neighborhoods—often inhabited by lower-income populations with limited capacity for resilience or recovery. This dynamic entrenches vulnerability in already marginalized communities, deepening the core-periphery divide that characterizes many Global South cities. Hence, flood risk management must transcend pure engineering solutions by integrating social justice considerations and inclusive planning frameworks.
Further complicating matters, the study’s integrated methodology—combining hydrodynamic modeling with depth-damage curves and fine-scale demographic data—is a significant advance in urban flood risk assessment. Depth-damage curves describe the relation between floodwater depth and economic loss for different types of buildings and infrastructure, enabling highly localized damage estimation that mirrors real-world heterogeneity in construction quality and property value. When linked with demographic information, such curves facilitate the identification of precise intersections between hazard exposure and social vulnerability, clarifying who benefits and who loses under different flood defense scenarios.
Moreover, the concept of the protection-induced time shift has profound implications for emergency management and disaster preparedness. Earlier flooding in downstream neighborhoods compresses the timeframe for evacuation and emergency response, increasing the risk of casualties and damage. Conversely, extended flooding-free windows for upstream wards provide a potential model for staged response strategies, where some parts of the city have more time to react while others require immediate attention. This temporal heterogeneity calls for an overhaul of traditional flood emergency protocols, urging the incorporation of real-time flood evolution modeling to optimize resource allocation and protect vulnerable populations.
The study’s focus on Surat is particularly telling, as many burgeoning cities in the Global South face similar developmental pressures and hydrological risks yet often lack comprehensive flood protection infrastructure. Unlike many Western cities with long-established full-coverage levee systems, urban centers like Surat are experimenting with partial defenses as incremental, cost-effective solutions to mounting flood threats. However, incrementalism is not without tradeoffs. These findings act as a cautionary tale for cities contemplating piecemeal structural interventions without complementary social policies or comprehensive, basin-wide flood management strategies.
Addressing these challenges requires integrated, multi-dimensional approaches that transcend engineering fixes alone. Combining partial structural defenses with nature-based solutions—such as wetland restoration, urban green spaces for water retention, and adaptive zoning regulations—could help distribute flood risk more equitably. Furthermore, investment in community engagement, disaster risk education, and robust early warning systems tailored to local socio-economic contexts is imperative to ensure that technical benefits do not inadvertently deepen social inequities.
This study marks an important milestone in rethinking urban flood protection, especially for cities with significant socio-economic diversity and rapid spatial transformation. By highlighting the hidden costs embedded within partial flood defenses, it calls for a fundamental reimagining of resilience strategies that prioritize not only economic efficiency but also fairness, inclusivity, and sustainable urban futures. Structural protection must be viewed not as a panacea but as a piece in the larger puzzle of adaptive, equitable urban water governance.
In conclusion, as climate change continues to escalate the severity of flood events worldwide, the insights gleaned from Surat’s partial levee experience offer vital lessons for policymakers and urban planners globally. While safeguarding metropolitan cores is essential for economic stability, the broader societal ramifications cannot be ignored. Flood risk reduction frameworks must evolve to incorporate spatial justice and temporal dynamics to ensure that protective measures do not inadvertently produce new forms of vulnerability. This balanced perspective can help secure truly resilient cities for all inhabitants, rather than a privileged few.
The path forward, therefore, rests on harmonizing flood defense infrastructure with socio-environmental equity, fostering knowledge exchange among scientific communities, and operationalizing these findings through inclusive governance mechanisms. As cities in the Global South strive to prepare for an uncertain hydrological future, informed research such as this will be invaluable in guiding actionable, context-sensitive solutions that safeguard lives and livelihoods across diverse urban landscapes.
Subject of Research: Urban flood risk, partial flood defenses, inequality, hydrodynamic modeling, flood damage assessment, temporal flood dynamics, spatial vulnerability distribution
Article Title: Partial flood defenses shift risks and amplify inequality in a core–periphery city
Article References:
Kumar, A.S., Majumder, R., Kapadia, V.P. et al. Partial flood defenses shift risks and amplify inequality in a core–periphery city. Nat Cities (2025). https://doi.org/10.1038/s44284-025-00299-7
Image Credits: AI Generated
