Climate Adaptation: Coastal, Flood, and Farming Systems

Climate adaptation is the process of adjusting to current and expected climate change in order to reduce harm and take advantage of opportunities; examples include coastal defenses, flood management and changes in farming, in contrast to mitigation, which reduces greenhouse gas emissions. In brief: adaptation can be protect (sea walls, flood barriers), accommodate (raised homes, flood-resistant crops), retreat (moving away from high-risk areas) or avoid (not building in danger zones). It works best when planned early, tailored to local conditions and combined with the involvement of communities, and it has to go along with emission cuts because there are limits to adaptation.

Some climate change is already unavoidable, so communities around the world are adapting. This guide explains the idea of adaptation, how coastal, flood and farming systems adapt, how adaptation is financed and where its limits lie, compares the options in a table, works through a cost-benefit example, outlines the history and corrects common mistakes.

What is adaptation?

Adaptation covers any action that reduces the vulnerability of people and ecosystems to climate impacts. It can be reactive (after an event) or planned and proactive (before it), and it includes hard engineering, nature-based solutions, changes in behavior, early warning and insurance, and policy and planning. Resilience is the ability of a system to absorb shocks and recover. Maladaptation is an action that increases risk or shifts it to others, for example a sea wall that worsens erosion nearby or air conditioning that increases emissions. Good adaptation takes account of uncertainty and avoids locking in measures that will not work if climate change turns out stronger.

How do coasts adapt?

• Protection: sea walls, dikes, storm surge barriers and beach nourishment. The Netherlands has a long tradition of dikes, and London has the Thames Barrier. Coastal cities such as Jakarta are building large sea walls.
• Nature-based defenses: restoring mangroves, salt marshes, dunes and coral reefs, which absorb wave energy and also provide habitat and fish. Bangladesh and Vietnam have planted mangroves along their coasts.
• Accommodation: raising buildings on stilts, building flood-proof structures, early warning systems and cyclone shelters. Bangladesh’s shelters and warning system have greatly cut cyclone deaths: the 1970 Bhola cyclone killed an estimated 300,000 or more people, while later cyclones with similar strength killed far fewer.
• Managed retreat: moving buildings and communities away from the most exposed areas, as in parts of Fiji and Alaska, or allowing the sea to flood farmland that is turned into marsh.
• Planning: restricting new building in flood zones and updating coastal maps and building codes.

How can floods be managed?

Heavier rainfall and higher seas increase flood risk. Responses combine several methods:

• Structural defenses: levees, flood walls, storage basins and removable barriers.
• Working with rivers: giving the water more room, as in the Dutch Room for the River program (2006–2015), which lowered floodplains, moved dikes inland and created side channels at more than 30 locations.
• Sustainable drainage in cities: green roofs, permeable paving, rain gardens, ponds and wetlands that slow and absorb runoff, an approach known as the “sponge city” in China.
• Upstream measures: planting trees and restoring wetlands and meanders to slow the flow.
• Forecasting and warning: flood forecasts, alerts, evacuation plans and community training.
• Insurance and finance: flood insurance and emergency funds, and building codes that require protective features.

How do farming systems adapt?

• Crop and variety changes: using drought-, heat- and flood-tolerant varieties (for example, submergence-tolerant rice), earlier-maturing varieties, or different crops.
• Timing and management: changing planting and harvesting dates and using forecasts and mobile phone advice.
• Water management: rainwater harvesting, small dams, drip irrigation, mulching and soil practices that retain moisture, such as the “zaï” planting pits used in the Sahel.
• Diversification: growing several crops, mixing crops and livestock and agroforestry, which spreads risk.
• Soil and land care: raising organic matter, reducing erosion and restoring degraded land. Farmer-managed natural regeneration of trees in Niger has restored millions of hectares.
• Risk transfer and information: crop and weather index insurance, early-warning systems, storage and market access.
• Livestock: shade, heat-tolerant breeds, and supplementary feed in dry periods.

In cities, heat action plans, cool roofs, urban trees and cooling centers protect people during heat waves. Ahmedabad in India introduced a heat action plan in 2013 after a deadly heat wave in 2010, and reported fewer heat-related deaths.

What are the limits and challenges?

Adaptation has limits. Some impacts, such as the loss of low-lying islands, glaciers and coral reefs, cannot be avoided if warming is high. Costs and capacity are unequal: low-income countries need money, technology and training, and the UN Environment Programme has estimated that the adaptation finance gap in developing countries is many times larger than the funds that are provided. Other challenges include uncertainty in projections, conflicts over land and resources, lack of data and weak governance. Adaptation therefore has to be accompanied by strong mitigation to limit the size of the problem, and by support for the most vulnerable.

Adaptation options compared

Worked example: costs and benefits

The values are hypothetical and illustrate how adaptation is evaluated.

1. Benefit-cost ratio: a flood defense costs 40 million to build and 1 million a year to maintain over 30 years. The total cost is 40 + 30 × 1 = 70 million. It prevents an expected damage of 4 million per year, so 30 years give 120 million. The ratio is 120 ÷ 70 = 1.7, so the benefits exceed the costs.
2. Flood probability: a flood with a 1-in-100 chance each year has a probability of 1 − 0.99³⁰ = 1 − 0.74 = 26% of occurring at least once in 30 years.
3. With climate change: if the same flood becomes a 1-in-50 event, the 30-year probability is 1 − 0.98³⁰ = 1 − 0.545 = 45%.
4. Raising a defense: if the design flood level rises by 0.3 m and the wall is 4 km long and 2 m high, adding 0.3 m of height requires an extra volume of 4,000 × 0.3 × 1.5 (average width) = 1,800 m³ (a simple estimate).
5. Crop adaptation: a drought-tolerant variety costs 5 more per hectare in seed and raises the yield in dry years by 0.4 tonnes per hectare. At a price of 250 per tonne, the extra income in a dry year is 0.4 × 250 = 100 per hectare, a net gain of 100 − 5 = 95. If dry years occur 1 year in 4, the average gain is 0.25 × 100 − 5 = 20 per hectare per year.
6. Insurance: a farmer pays a premium of 30 a year for index insurance that pays 400 in a drought. If a drought occurs 1 year in 10, the expected payout is 0.1 × 400 = 40 per year. This is more than the premium of 30, which means that the scheme is subsidized, because insurers normally charge at least the expected payout plus their costs.

How has adaptation developed?

People have always adapted to their climate, for example through irrigation, terracing and flood defenses. After the Dutch North Sea flood of 1953, the Delta Works were built. Climate adaptation became an international issue with the UN Framework Convention in 1992, which included commitments to help vulnerable countries. The Cancún Adaptation Framework (2010) and the Paris Agreement (2015) gave adaptation a place beside mitigation, with a global goal on adaptation. Many countries now have national adaptation plans. The Global Commission on Adaptation reported in 2019 that investments in early warning, resilient infrastructure, dryland farming, mangrove protection and water management could bring benefits much greater than their costs. Interest in nature-based and locally led adaptation has increased.

Which mistakes are common?

Mistake 1: Treating adaptation as an alternative to mitigation

Adaptation has limits and costs rise with warming. Without cuts in emissions, some impacts cannot be adapted to.

Mistake 2: Thinking that hard defenses are always best

Walls and barriers help, but they can fail, are costly and may transfer risk elsewhere. Nature-based and planning measures can be cheaper and have more benefits.

Mistake 3: Using one solution everywhere

Needs differ by place and community. Successful adaptation is based on local knowledge and involves the people affected.

Mistake 4: Waiting for certainty

Projections will always have uncertainty. Flexible, low-regret measures that bring benefits under many futures can be started now.