The recently launched Surface Water and Ocean Topography (SWOT) mission collected data on sea levels around two of the inhabited islands of Tuvalu, a nation in the South Pacific Ocean that has been threatened with sea level rise that substantially exceeds the global average.
The image shows two areas of red that indicate higher than normal sea levels around two of Tuvalu's inhabited islands, Nanumanga and Nanumea. The higher sea levels were likely caused by internal tides or circular currents called eddies. The SWOT data illuminates for the first time these small ocean features that, when they occur on top of rising sea levels, can lead to episodic flooding along coastlines. The Tuvalu data was collected March 21, 2023.
Rising seas are a direct consequence of climate change. On a global scale, the combination of warming ocean waters and ice melt from glaciers and ice sheets is leading to sea level rise that is occurring at an ever-increasing rate. The current rate of rise is more than 0.15 inches (4 millimeters) per year, an increase from 0.08 inches (2 millimeters) per year in 1993.
This seemingly small increase holds great significance for coastal communities that have seen more than a century of persistent sea level rise. The gap between the average high tide and flooding conditions has narrowed, and coastal impacts driven by sea level rise have increased in frequency and severity in recent years.
This is particularly true for low-lying island nations like Tuvalu, located about 620 miles (1,000 kilometers) north of Fiji. Sea level rise does not occur at the same rate everywhere across the globe, and can be exacerbated by natural ocean fluctuations that occur over time periods from years to decades. For Tuvalu, the amount of sea level rise has been substantially higher than the global average over the past three decades. The amount of rise, when coupled with Tuvalu's low land elevations, places the country increasingly under threat. In the near term, sea level rise will combine with naturally occurring ocean variability and storms to exacerbate events like coastal flooding. Monitoring and understanding sea level change is critical for Tuvalu and other low-lying island nations.
Launched on Dec. 16, 2022, from Vandenberg Space Force Base in central California, SWOT collected the Tuvalu sea level data during a period of commissioning, calibration, and validation. Engineers are checking out the performance of the satellite's systems and science instruments before the planned start of science operations in summer 2023.
SWOT was jointly developed by NASA and the French space agency Centre National d'Études Spatiales (CNES), with contributions from the Canadian Space Agency (CSA) and the UK Space Agency. NASA's Jet Propulsion Laboratory, which is managed for the agency by Caltech in Pasadena, California, leads the U.S. component of the project. For the flight system payload, NASA provided the KaRIn instrument, a GPS science receiver, a laser retroreflector, a two-beam microwave radiometer, and NASA instrument operations. CNES provided the Doppler Orbitography and Radioposition Integrated by Satellite (DORIS) system, the dual frequency Poseidon altimeter (developed by Thales Alenia Space), the KaRIn radio-frequency subsystem (together with Thales Alenia Space and with support from the UK Space Agency), the satellite platform, and ground operations. CSA provided the KaRIn high-power transmitter assembly. NASA provided the launch vehicle and the agency's Launch Services Program, based at Kennedy Space Center, managed the associated launch services.