For Miami, Sea Level Rise Has Already Gone Exponential

(AP story showing the effects of 9 inches of sea level rise over the last 100 years. What the story doesn’t mention is that half of this sea level rise has occurred within the past 16 years and fully a third of it has occurred within the past 5 years. Video source: Associated Press.)

This week, Miami is scrambling to deal with a flooding emergency.

But the cause is not the looming approach of a major hurricane or even a powerful tropical storm. The flood emergency for the coming three days is simply a seasonal astronomical high tide. Something they are now calling a King Tide. A condition that arises due to solar and lunar alignment a few times every year. A gravitational flux that pushes high tides another foot or so above the normal range.

Decades or even years ago, astronomical high tide wasn’t so much of a problem for Miami. Now, it means flooded roads and runways. It means salt water backing up through city drainage and municipal water systems. It means sea walls over-topped. It means lawns, properties and businesses covered in water.

The crisis is so serious that the city has already allocated more than 400 million dollars to deal with the problem. And this week, crews and flood prevention planners are scrambling to face the rising seas.

Rapidly Rising Waters

 

Miami Sea Level Trend

(Peak high tide trend from 1998 through 2014 shows sea levels rose by 4.3 inches over the past 16 years with most of the rise occurring since 2008. Image source: Dr. Zhaohua Wu, FSU)

At issue is the fact that Miami is facing a climate change driven sea level rise that is in the process of going exponential. A ramping rate of water rise that is being driven by a combination of glacial melt, ocean expansion due to warming, a backing up of the Gulf Stream which is raising waters all along the Eastern Seaboard, and a continuation of land subsistence in South Florida due to a variety of factors.

From 1914 through 1998, sea levels rose by an average of 0.06 inches per year — a rate that was barely noticeable to residents and city planners alike. But from 1998 to 2009 the pace increased to a more troubling 0.14 inches per year. And from 2009 to the present year the pace again jumped to a terrifying 0.67 inches per year.

An exponential rate of sea level rise that, in the past year alone, raised Miami’s surrounding ocean waters by 0.86 inches. Should the observed sea level rise over recent years continue, Miami will be facing 6-9 feet of additional water by the end of this century and not the 3-4 feet currently predicted.

Vulnerable Miami, South Florida

Miami is particularly vulnerable to such rapid rates of sea level rise for a couple of reasons. First, most of Miami is less than four feet above 20th Century sea levels. So even moderate rates of sea level rise put major portions of the city under water. Second, the city sits on porous limestone. The rock, riddled with holes, leaks like a sieve. So building sea walls won’t help Miami much as water will simply rise up through the rocks themselves.

Because Miami is so low-lying and surrounded on almost all sides by water, it is often seen as one of the most vulnerable cities to human-driven climate change. However, the geological conditions are not unique to Miami and remain a problem for almost all Florida cities. The porous limestone is a feature of the entire Florida Peninsula. So the problems Miami is facing now will become problems for hundreds of cities and communities up the coast and in more central regions of the state as well.

At most immediate risk is all of South Flordia. Miami-Dade and Broward Counties have about half of their residents living below the 4 foot above sea level line. Collier and Monroe counties also boast very large populations within just 4 feet of already rapidly rising seas. Such a rise would generate inland water upwelling throughout much of south Florida and the Everglades even as many coastal regions faced inundation. Small, low-lying islands and barrier zones would be swallowed by the sea or broken by incursions through weak points. The mangroves, already in retreat, would be swiftly beaten back. Inland lakes, invaded by higher pressure salt water from below, would also rise.

FinalUnifiedSLRProjection

(Sea level rise observations and projections through 2060 for Key West. Note that observations end at 2009 and that the tidal gauges have recorded a 3 inch sea level rise from 2009 through 2014 for Miami — already hitting the bottom range of expected sea level rise by 2030. Image source: Southeast Florida Regional Climate Change Compact Page.)

As an example, seasonal high tides are already having an effect on the Delray Beach region that is starkly similar to problems now plainly visible in Miami. In the historic Marina neighborhood, water bubbles up from storm drains and spills over the banks of the Intracoastal Waterway into streets.

Charle Dortch, a resident for 17 years said in a recent interview with the Sun Sentinel:

“It’s progressively getting worse. The water is coming up the roadway right into people’s front yards. It’s flooding the parking area. It’s coming up higher and higher every year.”

Links:

Water, Water Everywhere: Sea Level Rise in Miami

Southeast Florida Regional Climate Change Compact Page

Southwest Florida Governments Not Planning For Sea Level Rise

The Ocean is Already Higher

In Miami, The King Tide is Coming

Associated Press

Sea Level Rise: Everglades

Florida and Rising Seas

Dr. Zhaohua Wu, FSU

(Hat Tip to TodaysGuestIs)

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