'Groundwater inundation' doubles previous predictions of flooding with future sea level rise

November 11, 2012

Scientists from the University of Hawaii at Manoa (UHM) published a study today 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 UHM Water Resources Research Center and Charles Fletcher, UHM Associate Dean, found that the flooded area in urban Honolulu, Hawaii, including groundwater inundation, is more than twice the area of marine inundation alone. Specifically, a 1-meter rise in sea level would inundate 10% of a 1-km wide heavily urbanized area along the shoreline of southern Oahu and 58% of the total flooded area is due to groundwater inundation.

"With groundwater tables near the ground surface, excluding groundwater inundation may underestimate the true threat to coastal communities," said Rotzoll, lead author of the study.

"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, Principle Investigator on the grant that funded the research.

Groundwater inundation is localized coastal-plain flooding due to a simultaneous rise of the groundwater table with sea level. Groundwater inundation is an additional risk faced by coastal communities and environments before marine flooding occurs because the groundwater table in unconfined aquifers typically moves with the ocean surface and lies above mean sea level at some distance from the shoreline.

Rotzoll and Fletcher combined measurements of the coastal groundwater elevation and tidal influence in urban Honolulu with a high-resolution digital elevation model. With this, they were able to assess vulnerability to groundwater inundation from SLR.

"We used the digital elevation model with our improved understanding of groundwater processes to identify areas vulnerable to marine inundation and groundwater inundation," Rotzoll explained. "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."

Strong evidence on climate change underscores the need for actions to reduce the impacts of SLR. Groundwater inundation has consequences for decision-makers, resource managers, and urban planners and may be applicable to many low-lying coastal areas, especially where the groundwater table is near the ground surface and groundwater withdrawal is not substantial. However, groundwater withdrawals can be used to mitigate effects of a rising water table, even if it means pumping brackish water to avoid inundation.

The authors will present the findings from this paper at two international meetings: the Geological Society of America Annual Meeting (Charlotte, NC) and the American Geophysical Union Fall Meeting (San Francisco, CA).

The study's authors plan to substantiate their assessment of the groundwater table with further measurements throughout the coastal Honolulu caprock aquifer and improve understanding of the dynamics of the water table.
-end-
Rotzoll, K. and Fletcher, C.H. Assessment of groundwater inundation as a consequence of sea-level rise. Nature Climate Change, DOI: 10.1038/NCLIMATE1725

University of Hawaii ‑ SOEST

Related Sea Level Articles from Brightsurf:

Sea-level rise will have complex consequences
Rising sea levels will affect coasts and human societies in complex and unpredictable ways, according to a new study that examined 12,000 years in which a large island became a cluster of smaller ones.

From sea to shining sea: new survey reveals state-level opinions on climate change
A new report analyzing state-level opinions on climate change finds the majority of Americans believe in and want action on climate change--but factors like state politics and local climate play important roles.

UM researcher proposes sea-level rise global observing system
University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science researcher Shane Elipot proposes a new approach to monitoring global sea-level rise.

How much will polar ice sheets add to sea level rise?
Over 99% of terrestrial ice is bound up in the ice sheets covering Antarctic and Greenland.

Larger variability in sea level expected as Earth warms
A team of researchers from the University of Hawai'i (UH) at Mānoa School of Ocean and Earth Science and Technology (SOEST) identified a global tendency for future sea levels to become more variable as oceans warm this century due to increasing greenhouse gas emissions.

Sea-level rise could make rivers more likely to jump course
A new study shows that sea level rise will cause rivers to change course more frequently.

UCF study: Sea level rise impacts to Canaveral sea turtle nests will be substantial
The study examined loggerhead and green sea turtle nests to predict beach habitat loss at four national seashores by the year 2100.

Wetlands will keep up with sea level rise to offset climate change
Sediment accrual rates in coastal wetlands will outpace sea level rise, enabling wetlands to increase their capacity to sequester carbon, a study from the Marine Biological Laboratory, Woods Hole, shows.

How sea level rise affects birds in coastal forests
Saltwater intrusion changes coastal vegetation that provides bird habitat. Researchers found that the transition from forests to marshes along the North Carolina coast due to climate change could benefit some bird species of concern for conservation.

As sea level rises, wetlands crank up their carbon storage
Some wetlands perform better under pressure. A new Nature study revealed that when faced with sea-level rise, coastal wetlands respond by burying even more carbon in their soils.

Read More: Sea Level News and Sea Level Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.