early warnings are made
Disasters and their warning signs
Often there are warning signs well ahead of a hazard event. Weather
forecasters observe the start of hurricanes and storms and can calculate
future strength and tracks, vulcanologists can interpret telltale rumblings
below the earth, ecologists keep watch on conditions that favour locust
breeding, drought experts estimate the chances of refreshing rains,
oceanographers plumb the depths of the Pacific Ocean for signs of the
and plot the travel of ocean-crossing tsunamis caused by earthquakes.
Good early warning systems also need to consider community vulnerabilities
as well as the hazards. What are the early warning signs for vulnerability?
Key signs are growing poverty, environmental degradation, populations
crowded in risky locations, civil strife, and lack of
knowledge and preparedness.
All warning systems, however simple they may be, are based on some
idea of how the phenomenon behaves, whether it is a storm or a locust
a landslide or epidemic, a migration of people or the slow destruction
of a forest. Scientists call this idea the “model”, and
they use the model to say what is likely to happen next. In the simplest
model may amount to no more than common sense – for example the
recognition that poor people who have settled in a river valley will
lose their dwellings and all their belongings in even a small flood.
At the other extreme, models of the physics of the global weather system
are immensely complex and require large computers to do all their calculations
and produce detailed forecasts for the whole globe.
Warnings are never perfect
Predictions are never perfect or precise. There is always some uncertainty.
A hurricane may change course overnight or weaken; a tsunami may be
higher than expected; an earthquake may be likely in a broad region
location and time cannot be pinpointed. Often the warning may be expressed
statistically – for
example, as a 60% chance of an El Niño developing next year.
In addition, there is always a great deal of uncertainty about the social
components of an early warning, and about the specific human impacts
that might occur. This can make it difficult for decision makers to act.
Decision makers and those at risk must weigh up the chances and consider
the implications for their particular situation. Which option to follow – to
close down a subway and disrupt a city or let the city keep running and
risk chaos? To follow advice to evacuate or stay put and try to protect
your home? To plant drought-resistant seed knowing it will not produce
as much as the usual seed? Each person or community must make its own
judgment as appropriate to their own circumstances. In each case there
are costs of acting as well as costs of not acting.