Climate Resilience in Asia’s Mega Deltas: A Spatial Approach to Adaptation Planning

A study, Spatial Analysis and Cost-Benefit Assessment of Climate Change Adaptation in Rice-Based Agrifood Systems of Select Asian Mega Deltas, conducted by the International Rice Research Institute, Alliance of Bioversity International, and International Center for Tropical Agriculture (CIAT), supported by the Asian Development Bank, offers a comprehensive analysis of agricultural production systems across three countries and two of Asia's mega-deltas. It offers insights into delta planning and the cross-border climate challenges that require collaborative action.

The research, part of the CGIAR’s program “Securing the Food Systems of Asian Mega-Deltas,” aims to “climate-proof” agriculture in the Ganges Delta in Bangladesh and the Mekong Delta in Viet Nam and Cambodia and ensure food security and sustainable development for the millions who depend on these deltas.

Employing a food systems approach, the study reviewed different production models to explore more holistic adaptation options across agriculture subsectors (staple crops, horticulture, and aquaculture). It adopted a comprehensive analytical framework, including six interactive methods (Figure 1).

Figure 1. Analytical Framework of the Food Systems Approach to Adaptation Planning

Source: K. Nelson et al. Forthcoming. Spatial Analysis and Cost-Benefit Assessment of Climate Change Adaptation in Rice-Based Agrifood Systems of Select Asian Mega Deltas. IRRI and ADB.

First, a policy review was conducted to understand existing national adaptation strategies and priorities. Next, a spatial analysis of climate risks was conducted to identify the areas most vulnerable to hazards such as floods, droughts, and heat.

With a clear picture of the risks, the study turned to crop suitability analysis to map bio-physically suitable areas for selected crops. This analysis is linked to adaptive capacity and vulnerability assessments that considered socioeconomic, natural, institutional, and technological factors concerning rural communities.

A cost-benefit analysis evaluated the financial viability of different farming practices and adaptation strategies. Global and local market trends were also studied to understand the economic importance and potential for future trade of key commodities.

Mekong Delta
The Mekong Delta in Viet Nam has high agriculture productivity. The area is highly suitable for year-round rice cultivation, moderate to high suitability for watermelon, and seasonal suitability for maize. While its climatic and geographical conditions support year-round cropping, it faces considerable climate vulnerability.

Adaptive capacity also varies significantly in the area due to social and economic challenges (Figure 2). Regions, such as Can Tho and Kien Giang, have relatively high capacity due to good literacy rates, infrastructure, market access, and low poverty. In contrast, much of the Mekong Delta exhibits low to medium capacity due to physical, human, and economic limitations and high exposure to climate risks. This combination creates vulnerability hotspots in northern Long An, coastal Bac Lieu, and large parts of Kien Giang and Ca Mau.

Figure 2. Vulnerability Map of Mekong River Delta, Viet Nam

Integration of adaptive capacity, climate hazard, and sensitivity analysis of rice for wet and dry seasons.
Source: K. Nelson et al. Forthcoming. Spatial Analysis and Cost-Benefit Assessment of Climate Change Adaptation in Rice-Based Agrifood Systems of Select Asian Mega Deltas. IRRI and ADB.

Crop diversification can improve income and nutrition. For example, combining rice with cash crops like watermelon generates one to two times the annual net income of double or triple rice cropping. In coastal zones, rice-shrimp integration yields nearly 50% more profit than traditional rice models, while rice-vegetable systems outperform triple rice. However, weak value chains, underinvestment in technology and logistics, climate-induced threats like pests and diseases, and competition for water resources between agriculture and aquaculture hinder the development and sustainability of mixed systems. The growing global shrimp market presents a significant opportunity to expand the shrimp sector.

The situation is Cambodia is more precarious due to higher risks and lower adaptive capacity. Floods and droughts are more frequent, amplifying climate-related challenges. About half of the region, particularly in northern Kandal, Prey Veng, and Svay Rieng, has medium to high adaptive capacity, supported by stronger economic, human, and physical resources. However, areas like the southern districts of these provinces and Takeo are lagging behind. As a result, crop production in the northern and central parts of the delta is highly vulnerable due to low adaptive capacity and high-risk exposure.

Diversifying through rice-watermelon and rice-fish systems can generate approximately three times the annual net revenue per hectare compared to single or double rice cropping. Despite this potential, Cambodia’s low to medium product quality limits its export competitiveness against neighboring countries like Viet Nam and Thailand. While there is growing domestic and export demand for watermelon, realizing its potential requires investment in transport, storage, and post-processing infrastructure. The aquaculture sector, which is currently underdeveloped and mainly reliant on captured fisheries, also requires significant investment.

Ganges-Brahmaputra Delta
The Ganges-Brahmaputra Delta in Bangladesh shows significant regional disparities in adaptive capacity. Figure 3 shows how this worsens vulnerability to climate risks such as drought, flood, and heat stress.

Figure 3. Vulnerability Map of Ganges Delta, Bangladesh

Integration of adaptive capacity and climate hazard and change in the suitability of rice for Boro, Aus, and Aman.
Source: K. Nelson et al. Forthcoming. Spatial Analysis and Cost-Benefit Assessment of Climate Change Adaptation in Rice-Based Agrifood Systems of Select Asian Mega Deltas. IRRI and ADB.

The delta is highly suitable for crop production, particularly rice, with varying suitability for irrigated and rainfed varieties. Watermelon and maize also demonstrate good potential across the region.

However, the ability to adapt to the climate challenges is uneven. Areas with low adaptive capacity struggle due to physical, economic, and human capital deficits, as illustrated in Figure 3. This vulnerability is more pronounced in the eastern areas where serious climate problems and low adaptation capacity pose considerable risks. The central, northern, and southwestern areas also experience varying levels of vulnerability.

To enhance resilience, diversification is a promising strategy. Cost-benefit analyses show that combining rice with cash crops like watermelon, sunflower, and vegetables or integrating rice-fish farming can substantially increase incomes. For example, rice-based systems that include sunflower or watermelon can double annual income compared to traditional single-rice cropping. Similarly, higher-value aquaculture and vegetable production can yield more than 50% net revenue.

Despite these opportunities, Bangladesh remains a net importer of rice, hindered by outdated processing technologies that lead to low-quality output and, in some cases, negative returns for farmers. While the aquaculture sector has been expanding to meet domestic and international demand, it faces challenges such as difficult production conditions and stringent quality and safety standards in export markets. The fruit and vegetable sectors also remain underdeveloped and fall short of international standards.

Asia’s mega deltas face the dual challenges of climate change and food security for a growing global population. Tackling the climate challenges demands a comprehensive and nuanced strategy encompassing several key components, including investments in modernizing irrigation infrastructure, enhancing water management, and ensuring sustainable agricultural practices.

Developing processing facilities to create value-added opportunities for local produce and reduce losses can foster a more attractive environment for private sector investment in strengthened value chains, ultimately fostering economic resilience.

Based on the analysis, the following measures are recommended:

• Invest in capacity building to empower stakeholders at the local and national levels to effectively implement and manage adaptation strategies.
• Facilitate access to long-term financing that enables farmers and businesses in these regions to adopt innovative, climate-resilient agricultural practices without the immediate pressure of repayment.
• Explore climate-resilient agriculture options to help mitigate the adverse effects of climate change and ensure food security in the face of shifting weather patterns.
• Improve market linkages and processing capacity to facilitate better market access and the potential to improve farmers' incomes by selling higher-value products.

Adopting a holistic approach ensures that adaptation strategies are tailored to various contexts and effectively address multiple interconnected challenges in a cohesive manner.

The study also highlights the importance of inclusive and equitable climate change adaptation planning, emphasizing the needs of marginalized communities that are often disproportionately affected by climate change.

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