Closing data gaps can help Pacific Islands adapt to sea level rise
In July 2022, residents and visitors along southern Rarotonga in the Cook Islands were warned to evacuate due to imminent powerful swells . As forecasts predicted waves approaching five meters , businesses closed, while residents and tourists evacuated homes and hotels. When the high seas hit, they washed out roads and damaged coastal infrastructure .
As climate change continues to drive sea level rise, this event offers a sobering picture of the risks that coastal communities face. Sea level in much of the western tropical Pacific has risen 10–15 centimeters since 1993—close to or nearly twice the global rate—leading to a marked increase in the frequency of coastal flooding.
When world leaders meet at the UN General Assembly on 24 September to address the existential threats posed by sea level rise , they must consider how global commitments can translate into practical support for countries on the frontlines. The intergovernmentally agreed declaration to be adopted at the meeting puts knowledge, data and science first among its four pillars, calling for sustained, accessible and interoperable data systems. Among these, topographic and bathymetric data is crucial because nothing can be done without knowing the height of the land and the depth of the water beside it.
Closing data gaps is crucial for coastal adaptation
Understanding coastal risk requires two connected views. Topographic data maps land elevation. Bathymetric data maps the shallow seabed, reefs, lagoons and intertidal areas between the open ocean and shore. Both are essential because reefs influence how waves break and how much energy reaches land.
Unfortunately, for most of the Pacific, those maps do not exist. Many governments lack data detailed enough to show where water will travel during a storm surge, how deep flooding could become or which assets will be exposed under different scenarios. Without it, adaptation measures may be designed for the wrong level of risk or placed where they will not provide the greatest protection. Getting these decisions wrong can leave communities more exposed and make future adaptation more difficult and costly.
Light Detection and Ranging technology, or LiDAR, is the most effective way to close this data gap at scale. Aircraft-mounted lasers can map the ground beneath dense tropical vegetation rather than the tops of trees and buildings that satellite elevation data captures. Moreover, green-wavelength lasers reach through shallow water to map reefs and lagoons that boats cannot survey safely or efficiently. A single survey, flown to international hydrographic standards, produces a seamless picture from the reef edge to inland and becomes the evidence base for flood modelling, land-use planning, infrastructure design, emergency management and maritime navigation.
LiDAR has been used in the Pacific for more than a decade, including in the Cook Islands, Kiribati, the Marshall Islands, Samoa, Tonga, Tuvalu and Vanuatu. But coverage remains deeply uneven. A UNDP review of every LiDAR survey flown in the region between 2012 and 2025 finds that, of the Pacific people living in the low-lying coastal areas most vulnerable to sea level rise, only about three in ten live on ground that has been measured. Furthermore, fewer than one in ten square kilometers of nearshore reef and seabed has been surveyed at all.
The inequity is starkest among the atoll nations facing the greatest threat. Across Kiribati, the Marshall Islands, Tokelau and Tuvalu, only 15.6 percent of their combined land area has LiDAR coverage. Among these four, Tuvalu alone has complete national coverage; Tokelau has none. At historical rates, closing the regional gap could take many decades, and potentially more than a century. Pacific countries do not have that long.
Three steps to achieve LiDAR coverage
To close the Pacific’s LiDAR gap, three actions are needed:
- evelopment partners and climate funds should provide dedicated, sustained financing for systematic topographic and bathymetric surveys, prioritizing the most exposed and least-mapped communities.
- Regional organizations, technical partners and governments should agree common standards so that data collected under different programmes is consistent, interoperable and fit for climate-risk modeling and infrastructure planning.
- Countries should own and centrally manage their data, with systems and capacity to make it accessible across government agencies and, wherever appropriate, freely available for public-interest use. Coordination can prevent duplication and ensure one survey serves many sectors.
We know this works because Tuvalu has already done it. In 2019, the Government of Tuvalu, with UNDP support and funding from the Green Climate Fund, commissioned an integrated LiDAR survey of the land and nearshore waters of all nine islands. The entire country—roughly 500 square kilometers of land, reefs and lagoons—was captured in about 37 hours of flying.
For the first time, officials were able to model which areas would flood and to what depth under specific conditions. They could identify where storm surge and wave overtopping pose the greatest danger, assess safer sites for development and explain risks to communities using clear maps. The data has since informed road design, environmental assessments, shoreline monitoring and development planning , as well as the design of coastal protection works.
The survey was a fraction of the cost of the US$36 million project it informed, and it now underpins that project’s coastal adaptation works. It shows how a modest investment in foundational data can improve the targeting and durability of every investment that follows.
LiDAR cannot hold back the sea. But it can show, with precision, where the water is likely to go and what lies in its path. That is the difference between adapting on evidence and adapting on assumption.
Mapping a safer course for the future
The Pacific has already said what it needs. In April this year, the heads of the region’s national geospatial and surveying agencies met as the Pacific Geospatial and Surveying Council, convened by the Pacific Community (SPC). They called on development partners to invest in LiDAR and back a coordinated regional approach to acquiring it, rather than one survey at a time.
In the coming weeks, UNDP will publish a country-by-country assessment of LiDAR coverage across the Pacific, analyzing what closing the gap would take. When leaders adopt the declaration on sea level rise in New York on 24 September, they must also commit to acting on the best available data and find the finance to close the data gaps.