International SWOT mission can improve flood prediction

The satellite, a partnership between NASA and the French space agency, is set to help improve forecasts of where and when flooding will occur in Earth’s rivers, lakes and reservoirs.

Rivers, lakes and reservoirs are like the arteries of our planet: they transport life-sustaining water in interconnected networks. When Earth’s water cycle runs too fast, flooding can occur that threatens lives and property. That risk increases as climate change alters precipitation patterns and more people live in flood-prone areas around the world.

Scientists and water managers use many types of data to predict floods. This year they have a new tool at their disposal: freshwater data from the Surface Water and Ocean Topography (SWOT) satellite. The observatory, a collaboration between NASA and the French space agency, CNES (Centre National d’Études Spatiales), measures the height of almost all water surfaces on Earth. SWOT was designed to measure all major rivers wider than about 300 feet (100 meters), and preliminary results suggest it could look at much smaller rivers.

Stream meters can accurately measure water levels in rivers, but only at individual, often widely spaced, locations. Many rivers do not have any flow meters, particularly in countries without the resources to maintain and monitor them. Gauges can also be rendered useless by flooding and are unreliable when water overflows the riverbank and flows into areas they cannot measure.

SWOT provides a more complete 3D view of floods, measuring their height, width and slope. Scientists can use this data to better track how flood waters pulse across a landscape, improving predictions of where floods will occur and how often.

J. Toby Minear of the Cooperative Institute for Research in Environmental Sciences (CIRES) in Boulder, Colorado, is leading an effort to incorporate SWOT data into flood models. Minear is investigating how to incorporate SWOT data into the National Oceanic and Atmospheric Administration’s National Water Model, which predicts flood potential and timing along U.S. rivers. Freshwater SWOT data will fill in the gaps between gauges and will help scientists like Minear determine the water levels (heights) at which flooding occurs at specific locations along rivers.

He expects SWOT to improve the National Water Model data in multiple ways. For example, it will provide more accurate estimates of river slopes and how they change with flow. Generally speaking, the steeper the slope of a river, the faster its water flows. Hydrological modelers use slope data to predict the speed at which water moves through a river and out of a landscape.

The SWOT will also help scientists and water managers quantify how much water lakes and reservoirs can store. While there are about 90,000 relatively large reservoirs in the United States, only a few thousand of them have water level data incorporated into the National Water Model. This limits scientists’ ability to know how reservoir levels relate to surrounding land elevations and potential flooding. SWOT is measuring tens of thousands of American reservoirs, along with nearly all American natural lakes larger than two football fields combined.

Some countries, including the United States, have made significant investments in river gauging networks and detailed local flood models. But in Africa, southern Asia, parts of South America and the Arctic, there is little data on lakes and rivers. In such places, flood risk assessments are often based on rough estimates. Part of the potential of SWOT is that it will allow hydrologists to fill these gaps, providing information about where water is stored in landscapes and how much flows through rivers.

Tamlin Pavelsky, NASA’s SWOT freshwater scientist lead and researcher at the University of North Carolina at Chapel Hill, says SWOT can help address the growing threat of flooding caused by extreme storms fueled by climate change. “Think about Houston and Hurricane Harvey in 2017,” he said. “It is highly unlikely that we would have seen 60 inches of rain in one storm without climate change. Societies will need to update engineering design standards and floodplain maps as heavy rainfall events become more common.”

Pavelsky says these changes to the Earth’s water cycle are altering society’s assumptions about flooding and what a floodplain is. “Hundreds of millions of people around the world will be at greater risk of flooding in the future as rainfall becomes increasingly intense and population growth occurs in flood-prone areas,” he added.

SWOT flood data will have other practical applications. For example, insurers can use models based on SWOT data to improve flood hazard maps and better estimate an area’s potential risks of damage and loss. A major reinsurance company, FM Global, is among the current top 40 users of SWOT – a global community of organizations working to incorporate SWOT data into their decision-making activities.

“Companies like FM Global and government agencies like the U.S. Federal Emergency Management Agency can adjust their flood models by comparing them to SWOT data,” Pavelsky said. “Those better models will give us a more accurate picture of where and how often flooding is likely to occur.”

Launched on December 16, 2022 from Vandenberg Space Force Base in central California, SWOT is now in its operations phase, collecting data that will be used for research and other purposes.

SWOT was developed jointly by NASA and CNES, with contributions from the Canadian Space Agency (CSA) and the United Kingdom Space Agency. NASA’s Jet Propulsion Laboratory, managed for the agency by Caltech in Pasadena, California, is leading the U.S. component of the project. For the flight system payload, NASA provided the KaRIn instrument, a GPS scientific receiver, a laser retroreflector, a two-beam microwave radiometer, and NASA instrument operations. CNES provided the Doppler Orbitography and Integrated Radioposition Satellite System (DORIS), the dual-frequency Poseidon altimeter (developed by Thales Alenia Space), the KaRIn radio frequency subsystem (together with Thales Alenia Space and with the support of the Space Agency of the United Kingdom), 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, and managed associated launch services.

For more information on SWOT, visit:

https://swot.jpl.nasa.gov/.

Jane J. Lee / Andrew Wang
Jet Propulsion Laboratory, Pasadena, California.
818-354-0307 / 626-379-6874
[email protected] / [email protected]

Written by Alan Buis

2024-060