What happens when conditions change? Managing Mangrove Restoration through El Niño

Mangrove restoration begins with listening and learning. Practitioners work with communities and local partners to understand hydrology, elevation, sediment, ecological condition, patterns of resource use and the causes preventing natural recovery, then develop interventions around what they find. This diagnostic approach is central to Community-Based Ecological Mangrove Restoration (CBEMR) and the restoration resources developed by Mangrove Action Project.

But restoration landscapes do not remain static after that assessment is complete.

Water levels change. Channels shift. Sediment accumulates. Rainfall varies. Communities adapt how they use and manage coastal resources. Young restoration cohorts encounter conditions that may differ from those in which a project was designed. Sometimes those changes reveal vulnerabilities that were difficult to detect at the outset.

The developing 2026–27 El Niño provides an unusually clear test of this challenge. The World Meteorological Organization expects the established El Niño to strengthen into a very strong event, with a near-100% likelihood that it will persist through February 2027. For restoration practitioners, however, the important question is not simply whether El Niño will affect mangroves. It is how changing climatic conditions interact with particular landscapes and communities and whether we can recognize emerging risks early enough to make better decisions.

After more than three years of restoration through GMT’s Blue Carbon Corridor in North Sumatra, this is increasingly how we think about restoration risk: assessment should not end when implementation begins.

The same climate shock does not create the same restoration risk

A regional climate signal does not translate into the same ecological outcome everywhere.

Rainfall, freshwater availability, elevation, tidal position, sediment dynamics and hydrological connectivity all influence how much climatic stress reaches an individual mangrove system. Two sites experiencing the same weather can therefore respond very differently.

One restoration site may remain well connected to tidal channels and receive sufficient inundation to absorb a period of climatic stress. Another may occupy a higher elevation or have restricted water movement that becomes much more consequential when rainfall or water levels change.

Recent research by GMT Co-Founder and Executive Secretary Dr. Ryan Merrill describes this capacity as hydroecological buffering: the ability of local landscape and ecosystem conditions to moderate a wider climatic shock.

For restoration practitioners, this distinction matters because many of the same characteristics considered during site assessment – hydrology, elevation, hydroperiod, geomorphology, freshwater connectivity and sediment dynamics also influence how a restoration site responds when climatic conditions change. The Global Mangrove Alliance Best Practice Guidelines for Mangrove Restoration similarly emphasize understanding hydrology, hydrodynamics, sedimentation and other site processes when designing restoration.

These are therefore not only restoration design variables. They are part of the system that determines how climatic stress is experienced locally.

El Niño can put that system under unusual pressure. Conditions that appear adequate during favourable years may become limiting during an extended period of reduced rainfall, altered water levels or increased salinity. Recent ESCAP analysis of climate signals and mangrove risk highlights the importance of tracking rainfall, water levels and salinity alongside ecosystem conditions as El Niño and Indian Ocean Dipole conditions develop across Asia and the Pacific.

In this sense, an extreme climate event can act as a stress test, revealing differences between restoration sites that were previously difficult to observe.

Monitoring should help us question our assumptions

Restoration monitoring often focuses on outcomes: survival, growth, regeneration, canopy development or area under recovery.

Those indicators matter. But adaptive restoration asks something else as well:

Are the assumptions on which our intervention was based still true?

A restoration plan might assume, for example, that a site receives sufficient tidal inundation for establishment, that freshwater inputs keep salinity within an acceptable range, or that a particular elevation remains suitable for a planted cohort.

Changing environmental conditions can test those assumptions.

Increasing porewater salinity might indicate that freshwater or tidal buffering is becoming inadequate. Suppressed growth or regeneration failure may suggest that establishment conditions are changing. Canopy deterioration or localized stand mortality can provide more serious evidence that ecological stress is developing.

But these observations are not diagnoses by themselves. They are reasons to look more closely.

A struggling seedling does not tell us whether the problem is salinity, inundation, wave exposure, species–site mismatch, planting quality or something else. Nor will all important changes necessarily be captured by ecological measurements alone. Field teams and the people who live and work alongside mangroves often notice changes in water movement, fisheries, sediment, erosion or seasonal conditions long before they appear clearly in a dataset.

Monitoring becomes useful for adaptive management when these different forms of evidence help us ask better questions about what is changing and why.

The practical sequence is simple:

Observe the change. Listen to what people are seeing. Investigate the cause. Consider what can realistically be influenced. Then decide whether a response is warranted.

This makes monitoring part of an ongoing process of learning rather than simply a means of documenting success or failure.

Where do we still have room to act?

Understanding why a site is vulnerable leads to another question: is there something we can reasonably change?

Some sources of risk lie largely outside the control of a restoration programme. A project cannot change a regional rainfall deficit or prevent El Niño from altering wider climatic conditions.

But climate stress may interact with local constraints that can be influenced.

Restricted tidal exchange may be correctable. Project-controlled water infrastructure may be adjustable. Planting may be delayed or moved. Future restoration cohorts may be shifted towards elevations with more suitable inundation. Protection may be strengthened where young plants face increased physical disturbance.

Merrill’s research describes this dimension as actionability: whether there remains a realistic opportunity to influence the mechanism contributing to vulnerability.

This suggests four questions when monitoring identifies emerging stress:

• What appears to be changing?
• What might be driving that change?
• Which parts of that mechanism, if any, can realistically be influenced?
• Is there still enough time for a response to improve the outcome?

These questions should not be answered by project developers alone. Where decisions affect community access, livelihoods, water management or the future use of a landscape, the people who depend upon that landscape need to be part of understanding both the problem and the possible response.

The final question also matters because the options available can change over time.

An emerging hydrological constraint identified early may still be relatively straightforward to investigate and address. Once prolonged stress has resulted in widespread canopy deterioration or stand mortality, addressing the original mechanism may no longer recover what has already been lost.

This is where climate information becomes operationally useful. UNDRR’s work on El Niño and anticipatory risk management emphasizes using forecasts together with information on exposure and vulnerability to move from reactive response towards action before impacts materialise.

Early warning therefore matters not because every early signal demands action, but because it gives people more time to understand what is happening and consider their options.

Mitigation is not always intervention

There is a risk in treating adaptation as an instruction to intervene whenever vulnerability appears.

Even well-intentioned restoration interventions can create new problems when the diagnosis is wrong. Hydrological engineering can alter natural processes. Planting can be shifted into unsuitable areas. Decisions intended to protect restoration outcomes can also impose costs on people who depend on the landscape.

Sometimes the appropriate response will be to address a clear hydrological constraint or change a planting decision. Sometimes it will be to increase monitoring, protect natural regeneration or delay an intervention until conditions are better understood.

And sometimes the appropriate response will be to leave a functioning system alone.

This principle is increasingly central to restoration practice. The Global Mangrove Alliance’s recent practitioner guidance on what works—and what to avoid—in mangrove restoration stresses understanding site hydrology, elevation, salinity and sediment dynamics and addressing the causes of degradation rather than defaulting to planting.

Adaptive restoration therefore requires restraint as well as responsiveness. The objective is not to remove every risk. It is to understand which risks can reasonably be reduced, which require closer observation and which we may need to learn to live with—without shifting the costs of our decisions onto the communities least able to absorb them.

Putting this into practice during El Niño

The current El Niño gives GMT an opportunity to test and improve this approach across our restoration work in North Sumatra.

One area of particular interest is the interaction between elevation and tidal connectivity.

Higher-elevation restoration areas generally receive less frequent tidal inundation. If El Niño conditions contribute to periods of lower water availability, sites that already have relatively limited tidal access may experience greater water or salinity stress than better-connected areas closer to the coast.

GMT can explore this by combining plot-level elevation data with information on tidal connectivity, field observations of inundation, salinity, seedling performance and regeneration, and observations from the communities and field teams who know these landscapes closely.

Importantly, we do not want to assume the outcome in advance.

El Niño gives us an opportunity to test whether higher-elevation restoration areas actually become more stressed, whether particular hydrological conditions explain that difference and whether the effect is significant enough to change restoration decisions.

If monitoring suggests that some areas are drying or experiencing reduced tidal access, several responses might be considered. Existing plots may need closer monitoring. Planting could be delayed where establishment conditions are temporarily unfavourable. Future cohorts might be shifted towards elevations with more reliable tidal access. Where a correctable hydrological constraint is identified, addressing the mechanism may be more appropriate than changing planting itself.

Climate-related stress will also interact with the ordinary challenges of restoration.

GMT field teams will continue watching wave exposure, sediment conditions, barnacle pressure, species–site matching and planting quality. Experience in North Sumatra has already shown that practical responses can range from using natural materials to reduce wave exposure and protecting young seedlings from disturbance, to changing planting techniques and reconsidering where planting should occur.

Separating these causes matters. Similar symptoms can have very different mechanisms, and therefore very different responses.

In practice, we see four broad possibilities:

Adapt now where evidence is strong, the underlying mechanism is reasonably well understood and a response is likely to help.

Watch and learn where signs of stress are emerging but we do not yet understand enough to justify intervention.

Improve the next decision where current outcomes cannot readily be changed but the evidence can improve future site selection, planting or restoration design.

Leave alone where ecological processes are functioning and intervention would add risk without a clear benefit.

These are not rigid categories. They are ways of asking a more useful question of a broad climate forecast: what is happening in this particular landscape, why might it be happening, and what if anything should we do differently?

Restoration has to keep learning

El Niño will not affect every mangrove restoration site in the same way, and not every sign of stress will require intervention. That is precisely why the coming months matter.

They provide an opportunity to test whether assumptions made during restoration design continue to hold as environmental conditions change: where hydroecological buffering is strong, where vulnerabilities emerge, which early signals prove useful and where communities and restoration teams still have meaningful choices.

The lesson extends beyond El Niño.

Good restoration begins with understanding a landscape: its ecology, its history, why it has changed and how people live with and depend upon it. Adaptive restoration carries that same attention forward after implementation.

Environmental conditions will continue to change. Community priorities will evolve. Coastlines, hydrology and climate will not always behave as anticipated when a restoration plan is written. And our own understanding will sometimes prove incomplete.

The objective cannot therefore be to design a programme that predicts every problem correctly.

It is to build one capable of noticing when an important assumption may no longer hold, listening to the people closest to the landscape, investigating why, and being willing to change course when the evidence calls for it.