Tropical Cyclones

Physical Dynamics

In what follows, I'll make reference to features of Earth's global pressure and wind patterns (e.g., Trade Winds, subtropical high/Horse Latitudes)

Here is an idealized image of the global circulation that drives these prevailing surface patterns (hot air rises over the equator and cold air sinks over the poles, but the upper atmosphere flow doesn't go directly from the equator to the poles because of distortions caused by the earth's rotation. So air sinks back to the surface around 30° N and S to form the Horse Latitudes High and then diverge as the surface Trades and the Prevailing Westerlies. The Trades are very important to hurricane formation): https://web.archive.org/web/20100630204911/http://quakeinfo.ucsd.edu/~gabi/sio15/supps/prev-winds.gif

Tropical cyclones go by a variety of names in different locations: hurricanes in the Atlantic, typhoons in the Northwestern Pacific, and cyclones in the Indian Ocean, and, sometimes, chubascos along the west coast of Mexico

• These often form when the low pressure of an easterly wave deepens (the isobars would become "pointier" in their bend poleward -- as in the dashed lines on the sketch map below), as uplift is accelerated by unusual heat release during condensation.
  • Easterly waves are the ordinary storms of the Trade Wind belt (~5° - ~ 30° N or S). The convergence of air along the trough (or spine in the isobars), with poleward moving air "broadsiding" air moving west, causes uplift of air. Uplift results in air expansion and cooling, which eventually produces tall clouds and precipitation.
  • The Trade Winds are a prevailing wind pattern of air moving from the Subtropical High ("Horse Latitudes") toward the equator generally from east to west.
  • Isobars are lines on a map connecting places with the same barometric or atmospheric pressure. They're usually shown in hectopascals or (same thing) millibars.

  

• This becomes a self expanding process, because of the great amount of water vapor held in tropical maritime air over oceans. The uplift/condensation of that huge amount of water is a powerful source of heat energy to speed up the uplift and deepen the low pressure. This is because, when water condenses or freezes because of cooling, it releases latent heat into the air to enable it to make the phase shift downward to a less energetic state (from vapor to liquid or solid).

• A hurricane is seen on weather maps when the isobars keep bending until they cut themselves off into concentric circular patterns (instead of wavy zonal patterns) and when they attain hurricane force winds (118 km/h). They're called "tropical depressions" or "tropical storms" when they develop the circular isobar pattern but before their winds hit the requisite speed. Here is an interesting map from the Southern Hemisphere. An Easterly Wave is visible on the east (right) side of the map where the isobars bend toward the bottom of the map, toward the South Pole. The trough is shown as a dotted line there. To the upper left of the map, we see that a hurricane has developed its classic enclosed circular isobars off the northwest coast of Australia. There is also a peak of high pressure southwest of Australia.

  

• Description:

  • A hurricane is a circular center of very low pressure (a few have been known to plunge below 920 hPa, as did Typhoon Haiyan, which hit 895 hPa!)

  • This profound low draws in high speed winds: 120-200 km/h

  • The uplift of these swirling winds creates heavy rain (through convergent and convectional uplift).

  • The storm is usually relatively small, most commonly about 150-1000 km in diameter.

  • Hurricanes usually move about 25-30 km/h

    • They can stall, however, and just sit there, creating devastating amounts of rain and storm surge. The stalled Typhoon Nina and a cold front joined in China and produced the "2,000 year flood" in 1975, which led to the Banqiao Dam disaster, in which 62 dams failed one after the other along the Ru River in Henan Province, southeastern China

    • On the other hand, some hurricanes have been known to race along at up to 110 km/h (e.g., the "Long Island Express" of 1938)!

  • Perhaps the greatest peculiarity is the eye. This is a small area of absolutely clear weather right in the center of the storm. The eye is usually about 30-60 km across and can last an hour or so. Here is Typhoon Haiyan's:

    

  • The eye is produced by subsidence of air at the core of the spiraling storm. When air subsides or sinks, it is compressed as it descends under more and more of the overlying atmosphere. Compression concentrates the energy content of the air, and that produces warming. As air warms, it can hold more water as invisible vapor, so there's no more impetus for condensing, freezing, and precipitation, and the air clears.

  • Air races towards the center of a hurricane, spiraling around the column of sinking air to form a large vortex in the center, made up of rapidly uplifted air (and cooling, condensation, and precipitation). This forms the eyewall, the wall of immense cumulo-nimbus clouds around the eye. Here are NOAA images of Katrina's eyewall taken by their team of hurricane hunters who fly into these storms:

    

  • The wind at the top of the storm spirals outward for the most part, but some, trying to diverge, manages to head inward where it converges and most of it sinks. The subsiding air, of course, brings dry clear weather at the heart of the storm. Here is a diagram by NOAA:

    

  • Another distinctive feature is the spiral rainbands that swirl outward from the eyewall, rather like the arms of a spiral galaxy. These are made of cumulo-nimbus clouds formed from eddies or individual updrafts in the general inward rush of winds toward the center of the storm. The bands themselves spiral (counterclockwise in the Northern Hemisphere) slowly about the eyewall. They can stretch out anywhere from 75 to 750 km from the eye. They converge toward the eyewall, actually causing it to weaken sporadically, until the weakened eyewall is replaced by a converging rainband that then becomes the eyewall. This cycle of eyewall replacement may go on several times in a given storm.

  • Another feature of a hurricane is wind reversal after the eye passes. If you are in the direct path of a hurricane in the Northern Hemisphere, which is moving from east to west, the wind will first come at you from the north and you'll really get pounded, the winds accelerating as the eyewall approaches. Then, the eye passes over you, and things are sunny and tranquil for half an hour or an hour or so. Just when you start to relax, you'll be smashed by really fast winds, this time coming from the south. If the storm is coming up from the south to the north in the Northern Hemisphere, then the wind reversal would be easterly winds before the eye and westerly after. The opposite is true in the Southern Hemisphere.

  • Another feature of direct relevance to disaster planning is the notion of the (more) dangerous side. The winds spiral into the storm at some high rate of speed but you have to remember the storm itself is moving. You have to add and subtract the storm's speed to get the effective speed of winds in any part of the hurricane. In the Northern Hemisphere, the dangerous side is the right side; in the Southern, it's the left side. So, if the storm were moving, say, 25 km/hr westbound in the Northern Hemisphere and the winds were coming in at, say, 150 km/h, the winds to the right would effectively be moving at 175 km/hr, while those on the left side would effectively be moving at 125 km/hr.

    

  • Direction of travel: generally westward at first, driven by the easterly Trades and the circulation around the oceanic subtropical high cell. That said, hurricanes pretty much go where they "want" to, driven by quirks in their own internal circulation and interactions with the regional circulation. The regional circulation is itself affected by the position of the world pressure and wind belts (i.e., the Equatorial Low, Subtropical High, Subpolar Low, and the Polar High), seasonal movements in these (the whole system shifts north and south with the direct ray of the sun), and the land and sea pressure differential that is so prominent in the summer. Hurricanes will often initially start out westbound and then curve poleward along the isobars defining the Bermudas or Hawai'ian High (concentrated summer peaks of air pressure in the Subtropical High belt, which develop in the Atlantic and Pacific oceans, respecively). If there is a marked low on land produced by unusually hot weather, hurricanes will head for land. Here is a remarkable map by a Wikimedia Commons contributor, Nilfanion:

    

    • If they manage their poleward turn out at sea, notice how long their tracks can be. By staying out over water, they stay in contact with their power source: warm tropical water. By power source, I mean they pick up enormous amounts of evaporated water and the latent heat it carries, the air rises, cooling adiabatically enough to create condensation (clouds and rain) and this releases the latent heat, which accelerates the original uplift. Hurricanes can ride the Gulf Stream or similar warm currents pretty far poleward and can eventually head east along the current, moving along those summer isobar patterns into the Westerlies belt. Sooner or later, they degrade into lower power tropical or extratropical storms because they are slowly moving into ever cooler waters, which cuts them slowly off from their power source.

    • If they do their poleward swing onshore, they die suddenly. Notice how generally short the tracks are that come ashore and how quickly they degrade into the yellow tracks of an ordinary tropical storm or the green tracks of a tropical depression. This sudden flameout (if that's the right metaphor) is a result of the hurricane suddenly being cut off from access to its power source: warm tropical waters.

  • Global and yearly distribution. From the foregoing, we can generally predict where and when hurricanes are going to occur globally.

    • They are largely summer phenomena, given the influence of the oceanic cells into which the Subtropical High breaks during the summer: Hurricanes flow more or less along the curving isobars that encircle those oceanic peaks of high pressure. Hurricane season in the North Atlantic and North Pacific, then, is largely July to October; in the North Indian Ocean, there are two peaks, one in May and another in November. In the South Pacific and the South Indian oceans, it's more like late October to May.

    • Hurricanes are tropical but not equatorial. Why don't they form right along the equator, where, presumably, the ocean water is warmest? Because Coriolis Effect is non-existent. Coriolis Effect is the seeming deflection of a moving object (e.g.., wind) to the right (Northern Hemisphere) or to the left (Southern Hemisphere) produced by the rotation of the earth under it. There has to be some Coriolis Effect to induce the inspiraling so characteristic of these storms, and there is none along the equator. Hurricanes, then, generally originate somewhere between 8 and 15 degrees north or south of the equator.

    • They mainly afflict east coasts of continents (and islands en route) because of their dependence on a warm current, such as the Gulf Stream. We in California are protected from full-blown hurricanes by the cold California current. These systems sometimes generate some squall-line cloudiness and rain in California and western Mexico, occasionally called "chubascos." We sometimes get the tropical moisture from a chubasco, usually in August or September, receiving thunderstorms in the summer which, otherwise, is pretty rare for us.

    • An interesting gap is present on this map of typical hurricane storm tracks: the South Atlantic is free of them. Current debates focus on ocean temperatures in the South Atlantic just south of the equator (they may not break the 26° C threshhold that seems necessary to trigger hurricanes) and on vertical wind shear in the troposphere (lowermost atmospheric zone) there (too strong to support the vertical uplift of the eyewall).

  • There are several separate sources of hazard in a hurricane:

    • Extreme winds (Typhoon Haiyan's transiently reached 315 km/hr!)

    • Torrential rain and the resulting freshwater flooding and mudslides (which is what killed most of the more than 10,000 people who died in Hurricane Mitch in 1998).

    • Saltwater flooding from the storm surge and high winds.

      • The extreme low pressure of a hurricane actually pulls up the ocean surface in the area under it! This lump is further bunched by the winds. When this surge strikes the coast, waves can penetrate farther inland than they would otherwise, sort of the mother of all high tides in effect (and watch out if landfall coïncides with high tide!). In many ways, this resembles a tsunami. Here is a striking video by an eyewitness to the Typhoon Haiyan storm surge, showing that tsunami-like quality: https://www.youtube.com/watch?v=rS0gv4Xbw7w

      • Interestingly, sometimes the combination of surge and wind can make coastal rivers run upstream! This happened to the mighty Mississippi River during Hurricane Isaac in 2012! http://www.bbc.com/news/science-environment-19435026

      • Waves in water are a function of wind speed, duration, and fetch (the distance of open water in the direction the wind is blowing): Hurricanes generate really high wind speeds for a sustained period of time and the waves that come at a coast may have had a long stretch of open water.

      • So, you have really big waves and an elevated ocean surface and that translates into serious saltwater flooding along coastal lowlands.

      • Human life is endangered both by the possibility of drowning and by the debris carried by these waves that causes blunt-force trauma or wounds that can kill someone ... or knock them out so they drown. Again, this very much resembles how tsunami kill people.

    • The dangerous side of hurricanes also often spawns tornadoes to make the misery complete. This happened in Katrina.

  • Like the Fujita Scale with tornadoes, there is a hurricane intensity scale, which is called the Saffir-Simpson Scale. It has five hurricane levels, 1-5, covering damage levels from minimal to catastrophic:

          
    
                          Saffir-Simpson Scale
                          Type     Damage       Press: hPa  Wind: km/h  Surge: m
                                                                            
                          Depression (easterly wave develops circular isobars) 
                          Tropical storm (many hurricane traits,                                
    but not strong enough yet)
                          Hurr. 1  minimal         >980    <118        1.25-1.75       
                          Hurr. 2  moderate      965-980   118-154     1.75-2.75      
                          Hurr. 3  extensive     945-965   154-178     2.75-4.00      
                          Hurr. 4  extreme       920-965   178-210     4.00-5.50      
                          Hurr. 5  catastrophic   <920      >210         >5.50
    
    

Social Dynamics

For a hurricane to become a disaster, it needs people and property in the way. Mars develops hurricane-like storms around its north pole, complete with eyes, but these are not (yet) a natural hazard, because there are no people or assets at risk to it. Over the course of this century, hurricanes have become costlier and costlier as the human population grows and as it concentrates on hurricane coasts.

• A hurricane (called a "cyclone" locally) hit Bangladesh in 1970 and destroyed over 500,000 human beings.

• Hurricane Andrew did over $20 billion dollars of damage in 1992, because there are now so many people and economic activities and assets in South Florida. Deaths, however, were confined to 26-65 (depending on how you define hurricane-related death).

• Hurricane Katrina killed over 1,800 in the US and cost $108 billion.

• And the freak combination of Hurricane Sandy, an Arctic cold front, and an earlier contribution of hurricane moisture from southwest of Mexico (remnants of Hurricane Paul) that intensified a normal midlatitude wave cyclone, led to "Superstorm Sandy" in the American Northeast in 2012, with losses estimated at $75 billion and 233 lives.

• More recently, Typhoon Haiyan hit the Philippines in November 2013, the highest category storm ever to make landfall and the strongest wind speeds ever recorded at that time (315 km/hr sustained winds), with a central pressure of 895 hPa. It killed over 6,000 people in the Philippines and did nearly $3 billion in damage.

• Almost like a competition among hurricanes, 2015 saw Hurricane Patricia form in the eastern Pacific, off the west coast of Mexico, and it went from tropical storm to Category 5 monster in 24 hours, something of a record. It set the new record for the worst hurricane ever recorded (sustained winds at 215 mph or 345 km/hr) and central pressure of 872 hPa. It weakened before landfall and, luckily, hit a less-populated part of the coast, rather than the densely populated ports, and 8-13 people lost their lives. The storm did not quite half a billion in damage. This was a spctacular near-miss for Mexico.

Trends in Mortality

In the United States, at least, mortality in hurricanes has declined over the last century, from the staggering loss of over 8,000 people in the Galveston hurricane of 1900 and the deaths of over 2,800 people in the US and Puerto Rico in Hurricane San Felipe in 1928. With the exception of Hurricane Katrina in 2005, which killed over 1,800 people, in the US, hurricane mortality has declined to the tens to dozens range. So, in that sense, social vulnerability to hurricanes has decreased in the United States.

Globally, hurricanes remain major killers, with risk concentrated in much of Asia, Central America, and southeast Africa, as mapped by NASA's Socioeconomic Data and Applications Center (you need to set up a free account to access their data): here. The toll from individual events can be monstrous:

• Bhola Cyclone of 1970 struck India and Bangladesh (then known as East Pakistan), particularly the low-lying Ganges Delta area, costing anywhere from 300,000 to 500,000 deaths.
• Typhoon Nina in 1975 stalled over China and the massive flooding it caused triggered the failure of 62 dams, with estimated mortality at 171,000.
• Cyclone Nargis of 2008 devastated Southeast Asia, particularly the dictatorship of Burma (Myanmar), where it may have killed over 100,000 people.

Trends in Economic Losses

In the US, economic losses to hurricanes, calibrated for inflation, show an increase throughout the last century. Very disturbingly, however, there has been a substantial increase in the truly great hurricane losses, with the ten billion dollar plus hurricane débuting in 1965 (Betsy), followed by twelve more since then, of which nine came after 2000. Hurricane losses, then, seem to be mounting at an increasing rate in the US.

A sobering study by a company that does catastrophe modelling for insurers suggested that 28 hurricanes from 1900 to 2012, if repeated today, would each generate losses of at least $10 billion, with five of these topping $50 billion. So, the same hurricanes, recurring today, would cost an awful lot more as population and development have added to the vulnerability of the Hurricane Coast.

• Daraskevich, Glen. 2012. Historical Hurricaes that Would Cause $10 Billion or More of Insured Loses Today. Boston, MA: Karen Clark & Company.

There is a contrast in losses between developed and developing countries. Life loss in rich countries is low but economic losses are very high; life loss in poor countries can be very high, but the economic losses appear superficially to be small.

• Though the life loss in a hurricane can be staggering in Asia, Central America, and Africa, economic loss appears "trivial" in statistical reports because the capital lost (e.g., smallholder farmers' equipment and livestock, small business assets) adds to the millions of dollars, rather than the billions seen in many American hurricane disasters.

• To those suffering monetarily "trivial" losses, however, the losses are a huge proportion of their assets, meaning they cannot get back on their feet again, sometimes permanently.

• In the US, the monetary loss is staggering but it's a relatively small percentage of gross domestic product, so most people can recover at least partially, depending on their own particular vulnerabilities.

Trends in Social Vulnerability

Social vulnerability is different for people having different social positionalities. Social vulnerability is deepened by poverty, economic or social marginalization (class, ethnicity, caste, gender, age, religion, illness), living in great density on productive but flat and low-lying coasts and valleys that do not offer much possibility of evacuation, poor public risk communications systems, and may be worsened even more by a particularly dysfunctional government (such as Myanmar's).

An attempt to use geographical information systems (GIS) to analyze vulnerability to hurricanes, bringing together the geography of physical risks with the social and economic axes of vulnerability was done by a team at the National Center for Atmospheric Research, Purdue University, and the University of Iowa. This integrated Earth system science approach brought out the heightened vulnerability of populations quite far inland from the Hurricane Coast, poorer and more marginalized people living in foothill areas subject to the freshwater flooding of hurricanes. Some 63% of all hurricane fatalities in the US are inland, the result of flooding, mudslides, and tornadoes.

• Carroll, Dereka; Done, James; Ahijevych; and Villarini, Gabriele. 2012. Mapping social vulnerability to landfalling hurricanes in the Atlantic Basin. Poster presentation to unknown symposium.

• The map below uses light yellow to highlight those most vulnerable, from a combination of physical risk and socio-economic circumstances; the darkest reds are those least vulnerable.

  

Complicating variations in vulnerability, whether in the developing world or in the US or similar countries, are shifts in the risks of hurricane exposure. These shifts include:

• Changes in global climate: Physical risks increasing

  • Increasing buildup of carbon dioxide, methane, nitrous oxide, and other greenhouse gasses as a side effect of human economic activity. These let shortwave solar radiation in but absorb longwave radiation emitted by human activities, which delays its exit to space, effectively raising Earth's thermostat.

  • As temperatures rise, sea levels rise:

    • Glaciers are melting back in most places on Earth faster than ice can accumulate. and that new freshwater winds up in the oceans contributing to increasing sea levels. Nearly a third of current sea level rise results from glaciers melting and less than a fifth from melting of polar ice sheets
      • (Garner, Alex S.; Moholdt, Geir; Cogley, J. Graham; Wouters, Bert; Arendt, Anthony A.; Wahr, John, Berthier, Etienne; Hock, Regine; Pfeffer, W. Tad; Kaser, Georg; Ligtenberg, Stefan R.M.;Bolch, Tobias; Sharp, Martin J.; Hagen, Jon Ove; van den Broeke, Michiel R; and Paul, Frank. 2013. A reconciled estimate of glacier contributions to sea level rise: 2003-2009. Science 340 (17 May): 852-857. doi: 10.1026/science.1234532.

    • Sea surface temperatures are rising, and that causes thermal expansion of the upper ocean waters, which causes sea level rise. It seems responsible for about half the observed rise.
      • Riefbroek, Roelof; Brunnabend, Sandra-Esther; Kusche, Jürgen; Schröter, Jens; and Dahle, Christoph. 2016. Revisiting the contemporary sea-level budget on global and regional scales. Proceedings of the National Academy of Sciences of the United States of America 113, 6: 1504-1509. doi: 10.1073/pnas.1519132113.

  • Warm ocean water is, as we've seen, the power source of hurricanes, and human activity is increasing that power source.

    • This is not expected to increase the number of hurricanes.

    • It is, however, likely to increase the average intensity of hurricanes anywhere from 2-11% over current levels by the end of the century.

    • Moreover, it may create an increase in the relative frequencies of very intense hurricanes in comparison with all hurricanes (more category 3, 4, and 5 monsters).

    • It is also likely that the amount of rainfall generated by each hurricane will be as much as 20% greater than now.

    • A good overview of global warming and hurricanes can be found at the Geophysical Fluid Dynamics Laboratory at NOAA: http://www.gfdl.noaa.gov/global-warming-and-hurricanes

  • So, we can reasonably "look forward," not so much to more hurricanes, but more intense hurricanes on average, with greater freshwater flood capacities, a greater percentage of major hurricanes, probably with higher storm surges, hitting coastlines already affected by sea level rise and the increasing concentration of human populations and economic activities on hurricane coasts.

• Changes in human society

  • Population is growing worldwide and faster in poorer countries with substantial hurricane risk.

  • Globalization of the economy and the internal and external competition for resources is intensifying socio-economic polarization, deepening the vulnerability of the poor and marginalized. This kind of competition exacerbates any underlying prejudices in a population (religious hatreds, ethnic rivalries, sexual violence, exploiting the weaknesses of children, the elderly, and disabled). Any perceived advantages will be pressed in rough economic competition -- and during the turmoil following a hurricane or other disaster.

  • Much of the world's population is agricultural and agriculture puts a premium on tilling of low-lying, flat, fertile land, such as that along the hurricane coasts of the world and river valleys feeding into them.

  • Urbanization is going on all over the world and, in poorer countries, people losing their land or simply trying to make better opportunities for themselves are congregating in megacities, often in slums in extremely dangerous physical settings (e.g., landslide-prone hillsides): Many of Hurricane Mitch's fatalities were in such risky urban settings. Many great cities are coastal, having once been founded to support sea-based trade (e.g., New Orleans).

  • Wealthier people are also moving to hurricane coasts, seeking out the amenities of coastal living and warm climates. So, in the United States, the wealthy may be at heightened risk to hurricanes, though they may be able to externalize some of their vulnerabilities.

  • In all, then, there is an increase in human population on the hurricane coasts for a great variety of reasons, some concentrating homes of the well-to-do and others concentrating economically fragile and socially vulnerable populations on the coasts.

  • And all that human activity has as its side-effect the release of greenhouse gasses and the global warming that may be increasing hurricane intensities.

Risk assessment and risk management of huuricanes in a changing climate:

• From a de minimis perspective, the science has not yet evolved to be certain about trends in hurricane hazards. There are still a lot of "plot complications."

  • Hurricanes have fluctuated in numbers and intensity patterns over multidecadal cycles. In the Atlantic basin, for example, the number of hurricanes per decade varies from 12 to 24, while the number of major hurricanes varies from 1 to 10. The percentage of hurricanes classified as major varies from as little as 6.7% to fully 50.0%.

  • These variations are affected by such things as El Niño/La Niña cycles in the Pacific and the Atlantic Multidecadal Oscillation of sea surface temperature distributions.

  • Given this natural variability, it will be difficult to pick out the signal of anthropogenic climate effects (themselves quite complicated) from these natural sources of variability in a statistical sense (i.e., being able to say that there's less than a 0.05 probability that these random variations could cause a given level of increased hurricane activity and that human activity is the best alternative hypothesis). With more data, we may well be able to pick out the anthropogenic signal statistically, but we may never be in a position to say that Hurricane Thus-and-Such was caused by human activity. This is known as the "attribution problem." Interestingly, some new analytical methods may be cracking the attribution nut. Here is a link to a NOAA press release describing the attribution problem and introducing NOAA scientists' contributions to the Bulletin of the American Meteorological Society report, Explaining Extreme Events from a Climate Perspective, which you get to from https://www.climate.gov/news-features/understanding-climate/extreme-event-attribution-climate-versus-weather-blame-game. You can get the AMS Bulletin on extreme events here: https://www.ametsoc.org/ams/index.cfm/publications/bulletin-of-the-american-meteorological-society-bams/explaining-extreme-events-from-a-climate-perspective/

• From the precautionary principle point of view, we are facing one of those hazards that have massive consequences as well as tremendous lags among all the linkages in the interacting physico-chemical and human systems.

  • If we wait until we have enough data to be able to discern the anthropogenic signal from the natural climate variability cycles, we may no longer have the time or the technological power to stop runaway global warming: The momentum built into the system links may be unstoppable.

  • There is some consensus emerging in the scientific community that an increase in carbon dioxide from the current 395 415 parts per million (and the 280 ppm at the start of the Industrial Revolution) up to 400-550 ppm could result in runaway warming as each driving force triggers positive feedbacks in other drivers, amplifying the original warming. For example, warming sea surface temperatures trigger melting of Arctic Ocean sea ice, which darkens the polar regions and allows more solar energy to be absorbed rather than reflected, etc.

• So, climate scientists and hurricane meteorologists are sounding a clear alarm about global warming and its potential effects on hurricanes. Risk management decision-makers, particularly elected ones, may not want to face the economic and political consequences of reining in anthropogenic climate change, preferring a de minimis approach that enables delay in decision-making.

• Given that effective national or international decision-making is going to be a long time in coming, risk management is necessarily at a more local or regional scale. What can be done at these scales?

  • Zoning to reduce coastal construction and the concentration of human populations and assets along the hurricane coasts (politically challenging even at these scales)

  • Building up of coastal wetlands, such as the mangrove swamps of the American South, to serve as the first line of defense. Again, this is challenging at the local and regional scale, since the processes leading to the loss of wetlands (damming and levéeing upstream on the Mississippi watershed, oil and water extraction along the coast, sea level rise due to anthropogenic climate change, etc.) are taken at spatial and economic scales far beyond local and regional control. As if that weren't bad enough, sea level rise is creating a situation called the coastal wetland "squeeze": Wetland species depend on a particular elevation with respect to tidal flushing and salt concentrations. They will attempt to migrate inland as sea level comes up, but they will likely hit human construction and other obstacles in their paths.

  • Building up of seawalls and breakwaters that can reduce storm surge (and tsunami) damages. That is within the reach of most coastal communities in the United States. While it can mitigate smaller hurricane damages, it is possible that a very intense hurricane could destroy them (and add them to the debris flowing onshore).

  • Improving local and state building codes from engineering "lessons learned" in each hurricane. These may not protect a structure from the most vehement hurricanes, but they can reduce the expenses created by the more frequent, smaller magnitude hurricanes. Here are a few links to construction options:

    • Hurricanes: Science and Society Current and emerging technologies of hurricane protection

    • Lstiburek, Joseph. 2006. Flood and hurricane resistant buildings. Building Science Digest (Building Science Corporation) 111.

    • Wikipedia Hurricane-proof building

  • There are things individuals or households can do to reduce their vulnerability:

    • FEMA Ready.gov suggestions: Hurricanes

    • FEMA Ready.gov Evacuating yourself and your family

    • NOAA National Weather Service National Hurricane Center Hurricane preparedness -- be ready

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