世界银行-孟加拉国红树林海岸恢复力_潜在地点的识别_三重红利的评估和成本估算（英）-2025.7_52页_2mb

Summary of "Mangroves for Coastal Resilience in Bangladesh"

Core Content

This paper explores the potential of integrating mangroves into Bangladesh's coastal embankment system to enhance coastal resilience. It focuses on the triple dividends of mangroves: flood risk reduction, livelihood enhancement, and carbon sequestration. The study identifies suitable locations for mangrove restoration, quantifies their benefits, and estimates the associated costs to guide future policy and investment decisions.

Main Points

1. Bangladesh's Vulnerability and Coastal Protection Efforts

• Bangladesh is highly vulnerable to extreme weather events due to frequent flooding and low-lying geography.
• Climate change is expected to increase coastal flood risks.
• The Government of Bangladesh has upgraded its coastal embankment system, incorporating nature-based solutions like mangrove planting.
• Mangroves act as natural flood barriers by decelerating waves and reducing storm-surge heights.
• Existing mangroves are not currently integrated into embankment designs, which limits their potential benefits.

2. Potential Mangrove Locations

• The study uses a remote sensing approach to identify potential mangrove sites along Bangladesh's coastal zone.
• Identified sites include:
  • A belt south of Polder 45 (Amtali) with an average width of 1.77 km.
  • A belt around the Kukri-Mukri polder with an average width of 1.82 km.
  • Other notable areas include Sandwip and Mirersarai.
• These sites are located on the water side of embankments to maximize their protective role.
• Most identified sites have relatively narrow widths, with only 32 sites exceeding 500 m in width.

3. Triple Dividends of Mangroves

a. Flood Protection Benefits

• Mangroves can reduce wave loads and wave run-up, which in turn can lower the required embankment height and slope protection block size.
• In some areas, mangroves can reduce slope protection block size by up to 46% and shear stress by up to 55%.
• A mangrove belt of 500 m width can mitigate wave velocities by up to 90%.

b. Livelihood Benefits

• Mangroves provide provisioning services such as fisheries, timber, and recreational opportunities.
• 90% of commercial fish species in Bangladesh breed in the Sundarbans mangroves, contributing $158,360 in fishing revenue annually.
• Mangroves also support tourism, with 96,949 domestic tourists and 3,868 international tourists visiting the Sundarbans in 2014–2015.
• Livelihood benefits are estimated at over $22,000 per hectare.

c. Carbon Sequestration Benefits

• Mangroves can sequester up to 14 tCO₂ per hectare per year.
• Carbon service benefits are estimated at $13,120 per hectare over the period 2022–2050 at a 6% discount rate.
• The social cost of carbon (SCC) is used to estimate the value of avoided emissions, ranging from $89–$129 per tonne CO₂ between 2022 and 2050.

4. Methodology Overview

• Potential locations are identified based on existing mangrove presence, hydrodynamic conditions, and intertidal areas.
• Triple dividends are assessed using:
  • Hydrodynamic modeling to estimate flood protection benefits.
  • Meta-analytic value function transfer to estimate livelihood benefits.
  • Carbon sequestration models to estimate the economic value of carbon storage.
• Cost estimation is based on a meta-regression model that incorporates factors such as site area, GDP per capita, PPP, and the type of restoration intervention.

5. Key Findings

• Mangroves can reduce embankment design requirements significantly, with some sites offering up to 80% reduction in slope protection thickness.
• Carbon sequestration and livelihood benefits are substantial, indicating the potential for multi-benefit coastal protection strategies.
• Restoration costs vary with factors like site size, PPP, and the type of intervention (e.g., hydrological restoration + planting), with higher costs for combined interventions.
• The study highlights the need for comprehensive coastal assessments and site-specific feasibility studies to effectively integrate mangroves into embankment systems.

Key Information

• Mangrove belts with widths over 500 m are most effective for flood risk reduction and slope protection.
• Carbon sequestration is a significant co-benefit, with potential to support climate change mitigation.
• Livelihood benefits include fisheries, timber, and tourism.
• The estimated annual value of mangrove services is $22,000 per hectare, while carbon benefits are $13,120 per hectare.
• The study emphasizes the need for integrating mangroves into embankment designs for a triple dividend approach to coastal resilience.

Conclusion

The integration of mangroves into Bangladesh's coastal embankment system offers substantial benefits in terms of flood protection, livelihood enhancement, and carbon sequestration. The study provides a comprehensive assessment of these benefits, along with cost estimates, to guide future investments and policy decisions. It also identifies key research gaps and the importance of site-specific feasibility studies for successful implementation.