The next big question in sea level science: projecting regional changes (August, 2017)
Tuesday, August 22, 2017
“Sea level scientists have a pretty good grasp on global mean sea level,” said Steve Nerem, a professor in the Aerospace Engineering Sciences Department at the University of Colorado and the team leader for NASA’s Sea Level Change Team (N-SLCT). “It’s the regional sea level change that’s the next big question, the next big step for sea level science,” he added.
Regional sea level change is more variable, over both space and time, than global sea level change and can diverge by up to 20 centimeters (7 inches) or more from the global mean. Additionally, making regional projections about future sea level differs from making global mean sea level projections. This is due to the fact that different processes contribute to sea level change in coastal regions.
Global sea level rise is caused by thermal expansion of warmer water plus contributions from ice sheets and glaciers. Regional sea level change, especially along coastlines, is influenced by additional factors, including vertical land movements, waves and tides, and winds and storms. So in order to estimate sea level inundation and flood risk, scientists have to understand all the factors that contribute to extreme water levels such as local sea level rise, land subsidence, tides, waves and storm surge.
Stakeholders and decision makers are the ones driving the demand for improved regional sea level projections, Hamlington continued. “They’re the ones driving the discussion toward regional projections and that’s what’s needed for planning efforts.” These stakeholders include state and local public works officers responsible for infrastructure such as stadiums, roads, seawalls, and dykes plus pumps, water utilities, other utilities, businesses, and coastal inhabitants.
Scientists are responsible for helping society. This is why decision makers and scientists have come together to co-produce actionable science, to discuss how to communicate and collaborate, and to ensure that sea level science is being understood by the adaptation community.
“This is one of the biggest sea level conferences that we’ve had, when everybody who is working in different areas of the field comes together,” said Nerem. There were presentations on a variety of techniques to measure sea level change: tide gauges, measurements in marshes, paleo-sea level, corals, but from the perspective of the N-SLCT, “We’re really focused on how to use remote sensing, satellite altimetry from Jason-1, 2 and 3 and Gravity Recovery and Climate Experiment (GRACE) combined with GPS measurements to improve regional sea level measurements and projections.”
Nerem’s project targets regions around the globe that are susceptible to inundation but don’t have much measurement infrastructure, such as Bangladesh. Many of these regions do not have detailed digital elevation models or 50 years of tide gauge measurements like we do in the United States. “If we use our satellite techniques and test them in a place we understand, then we can go out where we don’t have that infrastructure and assess future sea level change in those regions.”
The N-SLCT hopes to leverage the satellite observations as much as possible to try to better understand future regional sea level change. This will help decision makers, coastal managers and stakeholders better adapt and prepare for the impacts of sea level rise.
According to Nerem, “We would like to produce a new assessment of future regional sea level change that benefits from the extensive record of satellite measurements collected by NASA.”