A U.S. Geological Survey report and a Maui News story on loss of sandy beaches to coastal erosion hinted at factors that are beyond the control of Hawaii planners and lawmakers - rising sea levels.
The May 10 news story ("Maui has lost more than four miles of sandy beach in past century," www.mauinews.com) noted that erosion and sea level rise inevitably will reduce Hawaii's high islands to low atolls over millions of years - as evidenced by the geology of the Northwestern Hawaiian Islands. But the story said not all of the erosion is the result of natural processes, citing effects of shoreline hardening - seawalls - that interferes with coastal processes and promotes loss of sand beach.
As lead investigator Charles "Chip" Fletcher says, "If you have a beefy seawall, it will protect the land for a few decades. It will destroy the beach and the beaches adjacent to it."
Fletcher, a University of Hawaii geology professor and coastal interface specialist, expands on that point in a book-length analysis, "Living on the Shores of Hawaii," published in 2010 by the University of Hawaii Press. Written with three colleagues, Fletcher's "Shores of Hawaii" details the long-term threat of sea level rise - from both natural and human causes - and the shorter-term impacts of human activities in coastal zones that facilitates erosion of sandy beaches.
Whether the causes are natural or anthropomorphic, Hawaii's islands are subject to the same impacts of sea-level rise affecting islands worldwide, notably the atolls of Vanuatu already suffering from shoreline erosion, saltwater intrusion in groundwater and storm inundation. A United Nations (www.un.org) 2009 report prepared by Pacific Small Islands Developing States, "Views on the possible security implications of climate change," notes:
"Today, sea-level rise is occurring at rates faster than existing models can account for, particularly the accelerating loss of ice from the West Antarctic ice sheet and Greenland. If the loss continues at its current rate, it portends sea level rise of 1 meter or more by 2100."
The USGS report says Hawaii has measured 1.5 millimeters of sea level rise over the past century, a relatively small amount but one that suggests long-term coastal loss is inevitable. The only issue then is the time frame for coastal loss - and current models for global climate change suggest sea-level rise is accelerating.
"The pattern of global sea-level change is complex because sea level is affected by winds and ocean currents, which also are changing," the USGS report says.
"In Hawaii, improving our understanding of the effects of sea-level change requires attention to local variability with careful monitoring and improved model efforts. Climate change is expected to cause sea-level rise to continue, and accelerate, for several centuries; and may exceed 1 meter about the 1990 level by the end of the 21st century."
"Shores of Hawaii" expands on the issue, noting that current scientific studies support a 1-meter rise in ocean levels, which "is a reasonable planning target for local coastal zone managers that is well supported by the research community."
The list of issues for Hawaii matches the effects observed on the small Pacific islands vulnerable to small increases in ocean levels. In addition to shoreline erosion and wave inundation, rising sea levels will induce saltwater intrusion into the water table and coastal ecosystems.
Curiously, the policy plan for the Maui County General Plan raises the issue of a 1-meter rise in sea levels by 2100.
"Projected sea-level rise over the next 20 years would increase at an exponential rate and would impact all coastlines, most severely affecting Maalaea, North Kihei, Lahaina, Kaanapali, Kahului and Kaunakakai. Prudent planning will consider projected sea-level rise as a variable in planning for each island," the policy plan says.
But the issue is not addressed further in documents prepared since.
* Edwin Tanji is a former city editor of The Maui News. He can be reached at hakumoolelo@earthlink.net. "Haku Mo'olelo," "writing stories," is about stories that are being written or have been written. It appears every Friday.
