Managing tropical cyclones: prediction, preparation and response

Overview

How cyclones are predicted and where forecasting falls short, the engineering, building design and land use measures used to prepare, and what response involves.

What you need to know

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Questions from this subtopic

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1. 1

   Distinguish between prediction, preparation and response as approaches to managing tropical cyclones.

   Model answer

   Prediction means detecting a storm and forecasting where it will go, how strong it will be and when it will arrive, so that a warning can be issued. Preparation, sometimes called protection or mitigation, means everything done in advance of any particular storm to reduce the damage it can do, from building codes and sea walls to evacuation plans and public education. Response means the actions taken once the storm has struck, from immediate search and rescue through relief to long-term reconstruction. Prediction buys time, preparation reduces the impact, and response deals with what remains.

2. 2

   How are tropical cyclones predicted?

   Model answer

   Geostationary and polar-orbiting satellites monitor the tropical oceans continuously, spotting developing disturbances and tracking cloud patterns, cloud-top temperatures and the formation of an eye. Buoys and ships supply sea surface temperature and pressure readings, and in the Atlantic reconnaissance aircraft fly directly into the storm to measure pressure and wind inside the eye. Radar tracks the storm and its rainfall once it comes within range of the coast. All of this data is fed into computer models that generate forecast tracks and intensities several days ahead, and the results are issued as watches and warnings with a cone showing the range of likely paths.

3. 3

   How reliable is the prediction of tropical cyclones, and where does it fall short?

   Model answer

   Forecasting of the track has improved greatly and a three-day forecast is now typically accurate to within about 150 kilometres, which is usually enough to warn the right stretch of coast. Forecasting of intensity remains much weaker, because rapid intensification in the last day or two before landfall depends on small-scale processes the models handle poorly, so a storm can jump two categories with little warning. The exact point of landfall, the height of the surge and the local rainfall totals are all harder to pin down than the general path, and warning a coastline hundreds of kilometres wide means evacuating many people who will not be hit, which erodes trust in future warnings.

4. 4

   What makes a warning system effective?

   Model answer

   The forecast has to be turned into a message that reaches everyone at risk in time and that they understand and act on. That means multiple channels, including radio, television, mobile phone alerts, sirens, loudhailers and village volunteers on bicycles for remote areas, and messages in local languages that state clearly what to do rather than quoting technical categories. A colour-coded or staged system, with a watch some days out and a warning as landfall nears, allows people to prepare in stages. Above all it needs enough lead time, ideally 24 to 72 hours, for people to secure property and move, and a population that has been educated in advance about what the warning means.

5. 5

   What structural or hard engineering measures are used to prepare for tropical cyclones?

   Model answer

   Sea walls, levees, embankments and breakwaters are built to hold back the storm surge, and floodgates and pumping stations protect low-lying cities. Rivers may be embanked or channelled to carry flood water away, and purpose-built cyclone shelters on raised platforms give communities somewhere safe within walking distance. Such schemes protect concentrations of high-value property effectively, but they are very expensive to build and maintain, they can be overtopped or breached by a storm larger than the one they were designed for, and they may give a false sense of security that encourages more building in the danger zone.

6. 6

   How can building design reduce the damage done by a tropical cyclone?

   Model answer

   Buildings can be given reinforced concrete frames and deep foundations, steeply pitched roofs firmly strapped to the walls so they are not lifted off, shatter-resistant glass or fitted storm shutters, and few openings on the exposed side. In flood-prone areas houses are raised on stilts or built with a solid ground floor used only for storage, and critical services such as generators are placed above expected flood levels. These measures work only if a building code exists, is designed for the storms the region actually gets, and is enforced by inspection, which is where the approach most often fails in poorer regions where people build their own homes from whatever they can afford.

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