Water, Water, Everywhere: Sea Level Rise in Miami

Like many low-lying coastal cities around the world, Miami is threatened by rising seas.  Whether the majority of the cause is anthropogenic or natural, the end result is indisputable: sea level is rising and it is due to climate change.  It is not a political issue, nor does it matter if someone believes in it or not.

Tidal flooding on the corner of Dade Blvd and Purdy Ave in Miami Beach in 2010. (Steve Rothaus, Miami Herald)

The mean sea level has risen noticeably in the Miami and Miami Beach areas just in the past decade.  Flooding events are getting more frequent, and some areas flood during particularly high tides now: no rain or storm surge necessary.  Perhaps most alarming is that the rate of sea level rise is accelerating.

Diving Into Data

Certified measurements of sea level have been taken at the University of Miami’s Rosenstiel School on Virginia Key since 1996 (Virginia Key is a small island just south of Miami Beach and east of downtown Miami).  Simple linear trends drawn through annual averages of all high tides, low tides, and the mean sea level are shown below, and all three lines are about 4.5″ higher in 2013 than they were in 1996.

vk_annualZooming in to daily data, let’s look at two representative months (nothing unique about them): January 1996 and January 2014.  Tidal predictions are calculated to high accuracy using dozens of known astronomical factors, but do not account for non-astronomical factors such as weather or sea level rise.  In 1996, the observed water levels were typically close to the predicted values… sometimes slightly higher, sometimes slightly lower due to meteorological influences.  In January 2014, however, there was still variability, but the tides were always higher than predicted.

Verified hourly water heights at Virginia Key, Jan1-Jan 31.  (NOAA/NOS)

Predicted (blue) and observed (green) hourly water heights at Virginia Key, Jan1-Jan 31. (NOAA/NOS)

As eluded to in the introduction, sea level is not just rising here, the rate of the rise is accelerating.  For the following chart, only the daily high water mark (highest of the two high tides) for every day for 18+ years is plotted.  The water levels at high tides are the most relevant because that is when flooding events are prone to occur.  The data are color-coded by 5-year periods (pink is 2009-2014, green is 2004-2009, blue is 1999-2004, and purple is the remainder: 1996-1999).  There is plenty of daily and intra-annual variability of course, but what stands out is the increasing slopes of the linear trends.  Over the past 15 years, the average high tide has increased by 0.19″/year, but over just the past 5 years, the average high tide has increased at a rate of 0.67″/year. tide_data

Exposure

The Miami metropolitan region has the greatest amount of exposed financial assets and 4th-largest population vulnerable to sea level rise in the world.  The only other cities with a higher combined (financial assets and population) risk are Hong Kong and Calcutta [1].

Using a sea level rise projection of 3 feet by 2100 from the 5th IPCC Report [2] and elevation/inundation data, a map showing the resulting inundation is shown below.  The areas shaded in blue would be flooded during routine high tides, and very easily flooded by rain during lower tides.  Perhaps the forecast is too aggressive, but maybe not... we simply do not know with high confidence what sea level will do in the coming century.  But we do know that it is rising and showing no sign of slowing down.

Map showing areas of inundation by three feet of sea level rise, which is projected to occur by 2100. (NOAA)

Map showing areas of inundation by three feet of sea level rise, which is projected to occur by 2100. (NOAA)

An Attack from Below

In addition to surface flooding, there is trouble brewing below the surface too.  That trouble is called saltwater intrusion, and it is already taking place along coastal communities in south Florida. Saltwater intrusion occurs when saltwater from the ocean or bay advances further into the porous limestone aquifer.  That aquifer also happens to supply about 90% of south Florida's drinking water.  Municipal wells pump fresh water up from the aquifer for residential and agricultural use, but some cities have already had to shut down some wells because the water being pumped up was brackish (for example, Hallandale Beach has already closed 6 of its 8 wells due to saltwater contamination).

Schematic drawing of saltwater intrusion.  Sea level rise, water use, and rainfall all control the severity of the intrusion. (floridaswater.com)

Schematic drawing of saltwater intrusion. Sea level rise, water use, and rainfall all control the severity of the intrusion. (floridaswater.com)

The wedge of salt water advances and retreats naturally during the dry and rainy seasons, but the combination of fresh water extraction and sea level rise is drawing that wedge closer to land laterally and vertically.

In other words, the water table rises as sea level rises, so with higher sea level, the saltwater exerts more pressure on the fresh water in the aquifer, shoving the fresh water further away from the coast and upward toward the surface.

Map of the Miami area, where colors indicate the depth to the water table.  A lot of area is covered by 0-4 feet, including all of Miami Beach. (Dr. Keren Bolter)

Map of the Miami area, where colors indicate the depth to the water table. A lot of area is covered by 0-4 feet, including all of Miami Beach. (Keren Bolter, FAU)

An Ever-Changing Climate

To gain perspective on the distant future, we should examine the distant past.  Sea level has been rising for about 20,000 years, since the last glacial maximum.  There were periods of gradual rise, and periods of rapid rise (likely due to catastrophic collapse of ice sheets and massive interior lakes emptying into the ocean). During a brief period about 14,000 years ago, "Meltwater Pulse 1A", sea level rose over 20 times faster than the present rate. Globally, sea level has already risen about 400 feet, and is still rising.

Observed global sea level over the past 20,000 years... since the last glacial maximum. (Robert Rohde, Berkeley Earth).

Observed global sea level over the past 20,000 years... since the last glacial maximum. (Robert Rohde, Berkeley Earth).

With that sea level rise came drastically-changing coastlines.  Coastlines advance and retreat by dozens and even hundreds of miles as ice ages come and go (think of it like really slow, extreme tides).  If history is a guide, we could still have up to 100 feet of sea level rise to go... eventually.  During interglacial eras, the ocean has covered areas that are quite far from the coastline today.

Florida's coastline through the ages.  (Florida Geological Survey)

Florida's coastline through the ages. (Florida Geological Survey)

As environmental author Rachel Carson stated, "to understand the living present, and promise of the future, it is necessary to remember the past".

What Comes Next?

In the next 20 years, what should we reasonably expect in southeast Florida?  The median value of sea level from various observed trends in 2034 is around 6", with a realistic range of 3-12".

Year by year, flooding due to heavy rain, storm surge, and high tides will become more frequent and more severe.  Water tables will continue to rise, and saltwater intrusion will continue to contaminate fresh water supplies.

This is not an issue that will simply go away.  Even without any anthropogenic contributions, sea level will continue to rise, perhaps for thousands of years.  But anthropogenic contributions are speeding up the process, giving us less time to react and plan.

The entire region is already considered high-risk by insurance companies because of the hurricane threat, so at some point, this additional gradual threat will likely lead to extreme-risk properties being uninsurable.

Coastal cities were built relatively recently, without any knowledge of or regard for rising seas and evolving coastlines.  As sea level rises, coastlines will retreat inward. Sea level rise is a very serious issue for civilization, but getting everyone to take it seriously is a challenge.  As Dutch urban planner Steven Slabbers said, "Sea level rise is a ... storm surge in slow motion that never creates a sense of crisis".  It will take some creative, expensive, and aggressive planning to be able to adapt in the coming decades and centuries.

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Special thanks to Keren Bolter at Florida Atlantic University and Dr. Shimon Wdowinski at University of Miami for their inspiration and assistance.

1. http://www.businessinsider.com/cities-exposed-to-rising-sea-levels-2014-4

2. http://www.climatechange2013.org/images/report/WG1AR5_Chapter13_FINAL.pdf

 

The Moore Tornado, and Common Tornado-Hurricane Misperceptions

On May 20, approximately two dozen tornado reports were scattered from Texas into Oklahoma, Kansas, Missouri, and Indiana.  Among them, one in particular combined two deadly ingredients: very intense winds and a populated urban area.  A tornado that struck Moore, OK (a southern suburb of Oklahoma City) was rated an EF5 tornado, with peak winds of 200-210mph.  An EF5 tornado contains the most violent winds on the planet — such winds are capable of leveling virtually any man-made building.

The large-scale setup for a severe weather outbreak was forecast at least a week in advance.  A 2-3 day period of all the necessary ingredients coming together at the same time was anticipated, and the peak threat was expected on May 20.  Indeed, on May 20, a tornado watch was issued for central and eastern Oklahoma at 1:10pm CDT.  Thunderstorms formed about 20 minutes later, and rapidly became severe, rotating supercells.  At 2:40pm, a tornado warning was issued for Moore, then at 3:01pm, a rare tornado emergency was issued.  From approximately 3:15-3:25pm, the massive tornado cut a path of destruction through the city, demolishing everything in its way and killing at least 24 people.

Radar image of the parent supercell that spawned the tornado. This image is from 3:21pm, just as the tornado was tracking through Moore. The magenta-purple blob is called a “debris ball”… rather than the radar beam reflecting off of just hail and rain, it’s also hitting a concentrated airborne ball of debris from houses and other structures. The radar itself is located at the center of the black circle east of Moore.

The tornado that passed directly over Moore was on the ground for 50 minutes and for 17 miles, and was at times about 1.3 miles wide.  This suburban town has been hit by significant tornadoes five times in 15 years: the October 4, 1998 F2, the May 3, 1999 F5, the May 8, 2003 F4, the May 10, 2010 EF4, and now the May 20, 2013 EF5.  (The original Fujita Scale from 1971 was replaced by the more accurate Enhanced Fujita Scale in 2007, and as such, the shorthand tornado rankings switched from F5 to EF5, for example.)  Not surprisingly, the odds of being hit by a significant tornado are climatologically quite high in central Oklahoma in May as seen in this map.

How Do Tornadoes and Hurricanes Compare?

Sometimes people erroneously interchange these two types of storms.  The only thing they have in common is strong winds; outside of that, they are entirely different phenomena.

1) Geography

In the U.S., tornadoes are most commonly found in the Great Plains states, but have been known to occur in almost every state.  They require a parent severe thunderstorm, and a list of atmospheric conditions that is fairly well-known.  If a tornado forms or passes over water, it’s called a waterspout, but for the most part, tornadoes “prefer” land.  Hurricanes, on the other hand, require a warm ocean to form and strengthen.  Once over land, hurricanes quickly weaken.  Only certain islands and coastal areas can be hit by a hurricane, though sometimes side effects can extend further inland (strong winds, flash flooding, tornadoes).

2) Intensity

While both types of storms are capable of producing destructive winds, tornadoes can become stronger than hurricanes.  The most intense winds in a tornado can exceed 300mph, while the strongest known Atlantic hurricane contained winds of 190mph.  The scales used to categorize the two are also different, as shown below.  Tornadoes are ranked on the Enhanced Fujita Scale, while hurricanes are ranked on the Saffir-Simpson Scale.  Beyond about 120mph, winds are powerful enough to significantly damage or destroy structures.

A visual comparison of the scales used for tornadoes and for hurricanes. On the top, the Enhanced Fujita Scale uses three-second wind gusts to define its thresholds. On the bottom, the Saffir-Simpson Hurricane Wind Scale’s thresholds are defined by one-minute sustained winds.

3) Size

While a very large tornado might reach 2 miles across, typically they are much less than a half mile across.  Hurricanes, on the other hand, are several hundred miles in diameter.  Even the eyewall (the inner ring of the most intense winds) is typically about 25 miles across.  Rainbands in the outer circulation of a hurricane can spawn multiple tornadoes simultaneously, while there is no way for the opposite to occur.  Tornadoes are completely dwarfed when it comes to a size comparison.

4) Predictability & Warning

There is also a huge difference in the timescales involved between tornadoes and hurricanes.  While the large-scale environment that is favorable for tornado development can be predicted several days in advance, there is presently no way of predicting individual tornadoes even HOURS in advance.  Once a rotating thunderstorm forms, there is still no way of knowing whether or not it will spawn a tornado, or how strong that tornado will become.  A tornado warning is issued an average of 13 minutes prior to impact, giving people a very limited amount of time to take shelter.  Sometimes that lead time is longer, sometimes shorter.  Conditions that are favorable for hurricane development can also be predicted several days in advance.  But since they usually form over the open ocean, they don’t immediately affect people.  There can be anywhere from a day to well over a week before the storm hits land… if it ever does at all.  Hurricane warnings are issued up to 36 hours before strong winds are expected to affect land, giving people time to prepare themselves and their houses as best they can.  Also due to the difference in time scales, people can evacuate an area prior to a hurricane landfall, but there is no time to evacuate an area before a tornado strikes.

5) Preparation

In both cases, having a plan in place before a storm comes is very important.  When the time comes, putting that plan into action will be stressful enough.  For a tornado, the most critical part of a plan is knowing where you and your family will take shelter; it might be an interior closet or bathroom, a basement, or a storm shelter.  Tornadoes are such short-fuse violent events that you may not have time for much else than protecting life.  Hurricanes are much easier to prepare for and allow for more elaborate planning.  You will have time to protect your house with window coverings, buy supplies, organize important documents, and evacuate if necessary.  If you don’t evacuate, then it’s very similar to a tornado: find the safest location you can to stay for the duration of the storm.  While a tornado will pass over in a matter of seconds or minutes, a hurricane will take several hours to pass over.  In both cases, no shelter is perfect — the most severe tornado or hurricane is capable of such destruction that even the best plan and best shelter may prove insufficient.  But clearly, there are ways to minimize your exposure to danger, and FEMA has some valuable information and resources available at http://www.ready.gov/tornadoes and http://www.ready.gov/hurricanes.

Author: Brian McNoldy,Senior Research Associate in Meteorology and Physical Oceanography at the University of Miami

Hurricane Researcher Brian McNoldy on the Science Behind Sandy

The following interview is featured in Outside Online in a series of interviews about Hurricane Sandy. To read the interview in full, click here.

A video showing Sandy’s life from October 23 to October 31: As Hurricane Sandy moved up the East Coast, a ridge of high pressure north of New Foundland blocked her from moving north and generated clockwise winds that pushed her into the East Coast, where she morphed with a cold front that had been moving east across the Eastern U.S. “The big picture of what made Sandy move north and then curve back northwest was really not having anywhere else to go,” says Brian McNoldy.

It was as a nine-year-old kid in Reading, Pennsylvania, that University of Miami scientist Brian McNoldy developed a fascination with hurricanes. “I think most of us have a storm,” he says. “Mine was Hurricane Gloria, in 1985.”

TV newscasters warned about the impending winds and rain. Local officials cancelled school for a few days. When the storm hit, it knocked out power. McNoldy went outside. “I can still remember how strong the winds were,” he says. “We didn’t get hit by the eyewall—just by the rainbands, but even that was pretty impressive.”

After earning undergraduate degrees in physics and astronomy at Lycoming College, a graduate degree in atmospheric science at Colorado State University, and picking up research experience at Colorado State University, he landed at the University of Miami in January of 2012. “This is an up-and-coming school in hurricane research, and there’s a lot of momentum going here,” he says. “I’m happy to have the opportunity to be part of it.”

For his job, he works on something called “vortex initialization code” for a joint project with the Navy. It’s a series of sophisticated computer programs that allow scientists to take a crudely-represented hurricane out of a model analysis, replace it with a more realistic hurricane that has tuneable factors (such as intensity, size of the storm, etc.), and see how changes affect the forecast.

When he’s not working on the vortex code, he writes about hurricanes. “I started what, at the time, wasn’t called a blog, because they weren’t really there yet, in 1996,” he says. “For any storm—not even a storm, for any wave in the Atlantic, I would have my little list of people who were interested in what was going on, and I would send updates to them during hurricane season. I’ve been doing that for 16 years now.”

His audience has grown. From 2007 to 2010, he was invited to blog about hurricanes for The New York Times. In 2012, he started blogging for the Washington Post and the Rosenstiel School of Marine and Atmospheric Science. On October 22, when Sandy was still Tropical Depression 18, he was one of the first to report on the likelihood of it turning into the Northeast U.S. with possibly devastating consequences. We caught up with him to learn a bit more about the science behind Sandy.

When did you start watching Sandy?
I think some of the models were picking up on something forming in the Western Caribbean probably by about October 12 or 13. Some models picked up, run after run, something that would form in the Western Caribbean, and then would move north toward Cuba. That persisted and they ended up being right. The National Hurricane Center issued the first advisory on Tropical Depression 18 on October 22, then upgraded it to Tropical Storm Sandy later the same day. It eventually headed north over Jamaica and Cuba. I thought, Wow, that’s extremely impressive for those models.
[Editor’s Note: Models are computer programs used to help forecast the formation and movement of tropical storms and hurricanes.]

On October 22, you blogged that there was a possibility it could hit the East Coast. How did you know that?
There are a few rather reliable global models. They’re models that run all the time, all year long, so they don’t focus on any one storm. They run for the entire globe, not just for North America. There are two types of runs these models can be configured to do. One is called a deterministic run and that’s where you get one forecast scenario. Then the other mode, and I think this is much more useful, especially at longer ranges where things become much more uncertain, is ensemble—where 20 or 40 or 50 runs can be done. They are not run at as high of a resolution as the deterministic run, otherwise it would take forever, but it’s still incredibly helpful to look at 20 runs.

Because you have variation? Do the ensemble runs include different winds, currents, and temperatures?
You can tweak all sorts of things to initialize the various ensemble members: the initial conditions, the inner-workings of the model itself, etc. The idea is to account for observational error, model error, and other sources of uncertainty. So you come up with 20-plus different ways to initialize the model and then let it run out in time. And then, given the very realistic spread of options, 15 of those ensemble members all recurve the storm back to the west when it reaches the East coast, and only five of them take it northeast. That certainly has some information content. And then, one run after the next, you can watch those. If all of the ensemble members start taking the same track, it doesn’t necessarily make them right, but it does mean it’s more likely to be right. You have much more confidence forecasting a track if the model guidance is in in good agreement. If it’s a 50/50 split, that’s a tough call.

To read the rest of the interview, click here.

Do you have any questions for Brian about Sandy or other Hurricanes? Leave them in the comments section below.

Joe Spring
Outside Magazine
Follow Joe on Twitter: @JoeSpring

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Potential Big Storm For Northeast U.S. Next Week

Just eight days after Sandy’s historic landfall near Atlantic City flooded hundreds of miles of coastline, and left nearly 8 million people without power, the Northeast U.S. could be in for another dose of Nature’s fury by the middle of next week.

Weather models are in agreement on a significant storm shaping up early in the week, then heading northeast along the coast and into New England. Unlike Sandy, this storm won’t have a name or tropical origins, but rather, fit the typical Nor’easter mold.

Two model’s depiction of the surface winds next Wednesday afternoon. The approximate track of the Low pressure from the Carolinas to its position on Wednesday is overlaid.

This storm will almost certainly *NOT* bring the same level of disastrous impacts to the region, but could easily bring unwelcome heavy rain and snow, strong winds, and of course, storm surge and coastal flooding from North Carolina all the way up to Maine -including New Jersey and New York. People in these areas are no strangers to potent Nor’easters, but they usually don’t have to face one immediately after a hurricane.

I will continue to monitor the long-range models for changes, but when the leading ones agree on something just five days away, it is a good sign that they’re onto something.

Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy

Superstorm Sandy Managed to Live Up to the Hype

For many, Sandy certainly lived up to the seemingly impossible forecasts of impacts. For starters, it made landfall with a central pressure of 946mb – the second lowest pressure ever recorded for any storm to hit the northeastern U.S. (first place was the 1938 Great New England Hurricane at ~941mb). Maximum sustained winds were 80mph, and higher gusts were reported from Rhode Island down to North Carolina.

The center came ashore near Atlantic City, NJ around 8pm EDT last night, though its effects were of course felt far from the center. This satellite image above shows Sandy at landfall on Monday evening.

In terms of a human toll, 84 lives have been taken by the storm (as of 9am Tuesday morning) across the Caribbean, the U.S., and Canada.

At least 7.5 million people in the northeast are without power. The only silver lining there is that the temperatures after the power outages aren’t sweltering or frigid, so it’s generally not as life-threatening as it could be.

The Battery in downtown NYC ended with a peak water level of 13.88′, which is about 2’8″ higher than the previous record (set in 1821). That, of course, resulted in a total catastrophe. By around 8pm, the subways and automobile tunnels were filling with sea water. And before that, both JFK and La Guardia airports had flood water pouring across the runways and into the terminals. The flooded areas of NYC also experienced large fires, collapsed buildings, and the power company shut off electricity to the city before the flooding got too bad and damaged the equipment. The iconic fishing pier at Ocean City, MD has been completely destroyed. The streets of Wildwood, NJ became the beach as the storm surge inundated the huge beach they used to have. The Atlantic City boardwalk is now rubble and the city flooded. The full range of impacts across all of the states are too numerous to detail here, but you will undoubtedly see and read more in the news.

A buoy at the entrance to the New York Harbor recorded a peak wave height of 32.5 feet, but I’m not yet aware of what affects such large waves had on the immediate area.

As of this morning, the Potomac River reached its highest level since 1996 due to the heavy rainfall. 5-7″ of rain fell in much of Maryland, Delaware, and northern Virginia; southern New Jersey received about 7-9″, northern New Jersey saw about 2-4″, while much of southest Pennsylvania was in the 3-5″ ballpark. Meanwhile, it’s still snowing hard West Virginia and they are expecting 2-3 feet of very wet snow.

It’s not over yet either. Heavy rain is still falling over an enormous area, and storm surge and coastal flooding continues to be a very large danger. This image shows the current radar depiction of the precipitation still affecting 17 states. I also have very long radar loops covering Sandy available: click here

Sandy will certainly be a storm for the record books, and will also end up being a retired name. Going back to 1953, the only storms so late in the alphabet to be retired were Stan (2005), Wilma (2005), and Tomas (2010).

Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy

Hurricane Sandy Expected to Make Historic Landfall Tonight

Hurricane Sandy continues to loom ominously off the U.S. east coast, bringing very heavy rain and tropical storm to hurricane force winds to many millions of people well before the worst arrives. The coastal flooding is already terrible, as expected (even as far south as Miami and Fort Lauderdale!). Locations from North Carolina to Maine will continue to see incredible coastal flooding/erosion, with the worst near and north of where the center crosses land (approximately southern NJ into NYC, Long Island, CT, RI, and MA). Inland flooding will also be a large problem in the coastal states as well as the inland states throughout the northeast. Finally, the 50-90mph winds that many places will experience can easily damage roofs, break tree limbs, and uproot trees, bringing power lines down with them.

At 8am EDT today, Sandy was a Category 1 hurricane with 85mph sustained winds, and a 946mb central pressure (it’s that very low pressure that creates the strong winds at the surface). The wind field is so large that tropical storm force winds (45mph+) extend 485 miles out from the center. The center is located approximately 300 miles south of NYC and 300 miles east of Norfolk – heading for a landfall late tonight near the Delaware Bay area. I have multiple long radar loops available at: click here.

Perhaps the trickiest part of this system from a warning perspective is that Sandy may not technically be a hurricane by the time it reaches the coastline later tonight. It is interacting with a cold front that is draped on the coastline and is losing some of its tropical characteristics. It actually has a warm front forming off to its east and a cold front to its south – a sign that it’s transitioning to an extratropical cyclone.

This absolutely does not make it any less dangerous! It has been intensifying (by both tropical AND extratropical mechanisms), and this interaction with the mid-latitude front is exactly what has been forecast to occur for days now. With or without a hurricane or a hurricane warning, this storm is extraordinary, unprecedented, and must be taken very seriously. The storms it has been compared to are the 1938 Great New England Hurricane, Hurricane Gloria in 1985, and the “Perfect Storm” of 1991. Sandy will join this crowd, and likely surpass some (if not all) of them in total impacts and damage.

This is truly a worst-case scenario that will cost many billions of dollars and claim hundreds of lives. Huge unthinkable storm surges along the entire northeast U.S. coast, mostly reaching their worst at night and during a full moon (already higher-than-normal tides), large rainfall amounts over several states, 2-3 FEET of wet snow in the mountains of WV, and widespread power outages for perhaps 10 million people.

If you’re in the affected areas, be aware of nearby streams/creeks/rivers that could quickly turn into white water rivers, large trees near your house, and be prepared to lose power for several days. Also, remember to check up on family and friends who might be at a higher risk than you.

Brian McNoldy
Senior Research Associate
& Author of Tropical Atlantic Update
Follow Brian on Twitter: @BMcNoldy