Reevaluating flood protection: disaster risk reduction for urbanized alluvial fans – Copernicus.org

Report on Geomorphic Hazards and Sustainable Development

Integrating Natural Hazard Management with Sustainable Development Goals

The management of geomorphic hazards, such as floods and debris flows, is intrinsically linked to the achievement of the United Nations Sustainable Development Goals (SDGs). An extensive body of research highlights the critical need for integrated strategies that not only mitigate disaster risk but also promote long-term resilience and sustainability. This report synthesizes key findings from scientific literature to frame hazard management within the context of the SDGs, particularly focusing on building resilient infrastructure (SDG 9), creating sustainable cities and communities (SDG 11), taking climate action (SDG 13), and protecting life on land (SDG 15).

Understanding Geomorphic Hazards: Alluvial Fans and Debris Flows

Characteristics of Alluvial Fans and Associated Risks

Alluvial fans are dynamic geomorphic features that pose significant risks to human settlements. Research has consistently demonstrated their susceptibility to unpredictable flooding and sediment deposition. The development on these landforms often overlooks their inherent hazards, leading to catastrophic consequences.

• Hazardous Environments: Studies by Bull (1977) and Harvey (2018) define the alluvial fan environment as prone to sudden channel shifts and widespread inundation, making sustainable development challenging.
• Urbanization Challenges: The urbanization of alluvial fans, as documented in cases from Israel (Grodek et al., 2000) and Italy (Santangelo et al., 2011), exacerbates flood risk, directly conflicting with the aims of SDG 11 (Sustainable Cities and Communities) to make human settlements safe and resilient.
• Risk Management Policy: Guidance from bodies like FEMA (1989, 2016) underscores the necessity of specialized risk analysis and mapping for alluvial fans to guide sustainable land-use planning.

Triggers and Dynamics of Debris Flows

Debris flows are rapid mass movements of water, sediment, and debris that represent one of the most destructive natural hazards in mountain environments. Understanding their triggers is fundamental to developing effective mitigation strategies aligned with global sustainability targets.

1. Climatic Triggers: Intense rainfall is a primary trigger, as evidenced by catastrophic events in Venezuela (Larsen et al., 2001) and the Sierra Nevada, USA (DeGraff et al., 2011). Climate change is expected to alter rainfall patterns, increasing the frequency of such events and highlighting the urgency of SDG 13 (Climate Action).
2. Land Use and Environmental Degradation: Research by Amaranthus et al. (1985) and Marden & Rowan (2015) links logging, forest roads, and other land-use changes to increased debris slide frequency. This connection emphasizes the importance of SDG 15 (Life on Land), which calls for the sustainable management of forests to maintain ecosystem stability.
3. Cascading Hazards: Major events like the Wenchuan earthquake (Tang et al., 2012; Xu et al., 2012) demonstrate how seismic activity can destabilize slopes, leading to subsequent catastrophic debris flows during rainstorms. This underscores the need for multi-hazard risk assessments in building resilient communities (SDG 11).

Aligning Hazard Mitigation with SDG 11: Sustainable Cities and Communities

Engineering Measures and Infrastructure Resilience

Structural flood protection and debris flow countermeasures are essential for protecting communities, but their design and maintenance must be considered within a life-cycle performance framework to ensure long-term sustainability and avoid unintended consequences.

• Check Dams and Mitigation Structures: The engineering of check dams and other torrent control works is a common mitigation strategy (Mizuyama, 2008; Chen et al., 2015). However, their potential for collapse or failure (Baggio & D’Agostino, 2022; Hübl et al., 2024) can exacerbate disasters, necessitating robust design and maintenance protocols to support SDG 9 (Industry, Innovation and Infrastructure).
• The Levee Effect: The work of Di Baldassarre et al. (2018) and Ding et al. (2023) warns of the “levee effect,” where structural protections can create a false sense of security and lead to more severe consequences when they fail. Sustainable floodplain management requires moving beyond reliance on hard engineering alone.
• Vulnerability of Infrastructure: Assessing the physical vulnerability of structures like check dams (Dell’Agnese et al., 2013) is crucial for life-cycle performance analysis (Ballesteros-Cánovas et al., 2016), ensuring that infrastructure remains effective over time.

Climate Action and Ecosystem Management (SDG 13 & SDG 15)

The Role of Climate Change in Hazard Intensification

Climate change directly impacts the frequency and magnitude of hydro-meteorological hazards. Addressing this link is central to achieving SDG 13 (Climate Action).

• Increased Wildfire and Debris Flow Risk: Climate change-induced declines in fuel moisture, as studied in the Pyrenees (Resco de Dios et al., 2021), can increase wildfire risk. Post-fire landscapes are highly susceptible to erosion and debris flows (Inbar et al., 1998; Rengers et al., 2024), creating a dangerous feedback loop.
• Effects on Debris Flow Patterns: Stoffel et al. (2024) provide a comprehensive overview of how climate change effects, such as altered precipitation regimes and glacier retreat, are modifying debris flow hazards globally.

Ecosystem-Based Disaster Risk Reduction (Eco-DRR)

Sustainable land management and the restoration of ecosystems offer a powerful, nature-based solution for disaster risk reduction, directly contributing to SDG 15 (Life on Land).

1. Forests as Protective Barriers: The historical use of afforestation for torrent control, such as in Canfranc, Spain (Rodríguez et al., 2022), demonstrates the long-term effectiveness of Eco-DRR in stabilizing slopes and mitigating hazards.
2. Integrated Water Management: The need to integrate flood and drought disaster risk reduction strategies (Ward et al., 2020) aligns with a holistic, ecosystem-based approach to water resource management, supporting SDG 6 (Clean Water and Sanitation).

A Framework for Sustainable and Resilient Hazard Management

Integrated Risk Assessment and Management

Achieving sustainable and resilient communities requires a shift towards integrated risk management frameworks that combine scientific analysis, engineering, and policy in alignment with the SDGs.

• Stochastic Life-Cycle Performance: Analyzing the performance of mitigation measures over their entire life cycle, considering various hazard scenarios, is essential for sustainable investment (Ballesteros-Cánovas et al., 2016).
• Holistic Floodplain Management: Reversing the levee effect and adopting more sustainable floodplain management practices are critical for long-term resilience (Ding et al., 2023).
• Decision-Support Tools: The use of cost-benefit analysis and other decision-support tools can help ensure that disaster risk reduction measures are both effective and economically viable (Mechler et al., 2014).

Analysis of Sustainable Development Goals in the Article

1. Which SDGs are addressed or connected to the issues highlighted in the article?

1. SDG 11: Sustainable Cities and Communities
   • The article’s references extensively cover topics like flash floods, debris flows, and their impact on urbanized areas and human settlements (e.g., Santangelo et al., 2011; Schick et al., 1999). The focus on hazard management, risk analysis, and protecting infrastructure within communities directly aligns with making cities and human settlements inclusive, safe, resilient, and sustainable.
2. SDG 13: Climate Action
   • Several references address the link between climate change and the frequency or intensity of natural disasters. For instance, Stoffel et al. (2024) explicitly discuss “Climate change effects on debris flows,” and Resco de Dios et al. (2021) mention how climate change may increase fire risk in mountain forests, a known trigger for erosion and debris flows. This connects directly to taking urgent action to combat climate change and its impacts by strengthening resilience.
3. SDG 15: Life on Land
   • The article includes studies on the effects of land use, such as logging and forest fires, on slope stability and sediment generation (Amaranthus et al., 1985; Marden and Rowan, 2015; Inbar et al., 1998). This highlights the connection between the management of terrestrial ecosystems (particularly mountain forests) and the prevention of land degradation and disasters like debris slides, aligning with the goal of protecting and restoring life on land.
4. SDG 9: Industry, Innovation and Infrastructure
   • A significant portion of the references deals with engineering measures for disaster mitigation, such as check dams, levees, and other protective structures (Chen et al., 2015; Mizuyama, 2008). The analysis of their effectiveness, failure, and life-cycle performance (Hüble et al., 2024; Sánchez-Silva et al., 2011) relates to the goal of building resilient infrastructure.

2. What specific targets under those SDGs can be identified based on the article’s content?

1. Target 11.5: By 2030, significantly reduce the number of deaths and the number of people affected and substantially decrease the direct economic losses relative to global gross domestic product caused by disasters, including water-related disasters, with a focus on protecting the poor and people in vulnerable situations.
   • The article is replete with case studies of catastrophic floods and debris flows that caused significant loss of life and economic damage (e.g., Alcoverro et al., 1999 on the Biescas flood; Larsen et al., 2001 on the Venezuelan disaster). The focus on “Fatalities from Debris Flows” (Prakash et al., 2024) directly addresses the core of this target.
2. Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries.
   • The entire theme of the article revolves around understanding, managing, and mitigating natural hazards like floods and debris flows. References discussing risk analysis (Ballesteros-Cánovas et al., 2016), hazard management policies (Flez and Lahousse, 2004), and ecosystem-based disaster risk reduction (Rodríguez et al., 2022) are all examples of efforts to strengthen resilience and adaptive capacity.
3. Target 15.3: By 2030, combat desertification, restore degraded land and soil, including land affected by desertification, drought and floods, and strive to achieve a land degradation-neutral world.
   • The article references studies on erosion processes after forest fires (Inbar et al., 1998) and the impact of logging on debris slides (Amaranthus et al., 1985). These studies are fundamental to understanding land degradation processes that exacerbate flood and landslide risks, thereby informing actions to combat them.
4. Target 9.1: Develop quality, reliable, sustainable and resilient infrastructure… to support economic development and human well-being.
   • References discussing the design of engineering measures (Chen et al., 2015), the simulation of check dam collapse (Baggio and D’Agostino, 2022), and the protection of critical infrastructure like the Canfranc International Railway Station (Fabregas et al., 2012) directly relate to the development and maintenance of resilient infrastructure against natural hazards.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

1. Indicator for Target 11.5: Number of deaths, missing persons, and directly affected persons attributed to disasters.
   • This is directly implied by the reference from Prakash et al. (2024), titled “Fatalities from Debris Flows: Worldwide Distribution and Trends,” which involves the collection and analysis of data on deaths caused by a specific type of disaster. Numerous other case studies of catastrophic events (e.g., Süveges and Davison, 2012 on the Venezuelan catastrophe) also inherently involve counting fatalities and affected populations.
2. Indicator for Target 13.1: Adoption and implementation of national and local disaster risk reduction (DRR) strategies.
   • The article references the UNDRR (2024) initiative and studies on “Ecosystem-Based Disaster Risk Reduction (Eco-DRR)” (Rodríguez et al., 2022) and “natural hazard management policy” (Flez and Lahousse, 2004). These titles imply the existence, analysis, and promotion of DRR strategies, which is the core of this indicator.
3. Indicator for Target 15.3: Proportion of land that is degraded over total land area.
   • While not explicitly stated as a proportion, references studying the effects of land use on slope failure and sediment generation (Marden and Rowan, 2015) and runoff and erosion processes after forest fires (Inbar et al., 1998) provide the scientific basis for assessing land degradation, a key component of this indicator.
4. Indicator for Target 9.1: Damage to critical infrastructure due to disasters.
   • The progress towards resilient infrastructure can be measured by tracking its performance during disasters. References analyzing check dam failures (Hüble et al., 2024), assessing the physical vulnerability of dams (Dell’Agnese et al., 2013), and evaluating the effectiveness of protection measures for infrastructure (Fabregas et al., 2012) imply the measurement of infrastructure damage and resilience as a key metric.

4. Summary Table of SDGs, Targets, and Indicators

Source: nhess.copernicus.org