Scientists from the University of Hawaiʻi at Mānoa published a study in Nature Climate Change showing that besides marine inundation (flooding), low-lying coastal areas may also be vulnerable to “groundwater inundation,” a factor largely unrecognized in earlier predictions on the effects of sea level rise (SLR). Previous research has predicted that by the end of the century, sea level may rise 1 meter.
Kolja Rotzoll, postdoctoral researcher at the Water Resources Research Center and Charles Fletcher, associate dean for academic affairs at the School of Ocean and Earth Science and Technology, found that the flooded area in urban Honolulu, Hawaiʻi, including groundwater inundation, is more than twice the area of marine inundation alone. Specifically, a 1-meter rise in sea level would inundate 10 percent of a 1-km wide heavily urbanized area along the shoreline of southern Oʻahu and 58 percent of the total flooded area is due to groundwater inundation.
“This research has implications for communities that are assessing options for adapting to SLR. Adapting to marine inundation may require a very different set of options and alternatives than adapting to groundwater inundation,” states Fletcher, principal investigator on the grant that funded the research.
“We used the digital elevation model with our improved understanding of groundwater processes to identify areas vulnerable to marine inundation and groundwater inundation,” explained Rotzoll, lead author of the study. “It turned out that groundwater inundation poses a significant threat that had not been previously recognized.”
Although effects of SLR on coastal areas have been discussed for a long time, this study is the first to explicitly assess the effects of including groundwater dynamics.
“Finding that the inundated areas double when including groundwater inundation in coastal flooding scenarios will certainly be a surprise for everyone assessing the effects of SLR without considering the local groundwater table,” said Rotzoll. “We hope other coastal communities use our research as the basis for conducting their own localized analysis.”
The authors will present the findings from this paper at two international meetings—the Geological Society of America Annual Meeting in Charlotte, N.C. and the American Geophysical Union Fall Meeting in San Francisco, Calif.
—Adated from a UH Mānoa news release