In areas of similar population densities, the number of victims may be expected to be larger for disasters of geological origin, such as earthquakes and volcanic eruptions, than for those of hydro-meteorological origin, such as floods, hurricanes, cyclones and droughts (ECLAC 2002). Yet, the latter tend to affect larger geographical areas, while those of geological origin tend to have more localised effects. Earthquakes tend to cause more destruction of capital stock in physical and social infrastructure than floods and droughts, which tend to cause more production and indirect losses. When an earthquake causes floods and landslides, production and indirect losses can also be significant. Most disaster risk phenomena take place in a sudden manner (earthquakes, floods), although there are cases where occurrence may be slow, like in the case of droughts. Droughts are different because they are intrinsic to the natural variability of almost all climates.
13.1 RELSAT - A participatory early-warning system for floods
In 1999 the European Union introduced flood early-warning systems in several Central American countries. In higher areas or upper river reaches, water levels are continuously measured and monitored, and this information is then transmitted by radio or other means to a local base for evaluation. The latter assesses risk based on the data received, and can predict whether, when and where flooding may take place. In the event, the staff of the local base can then alert the local institutions in charge of carrying out specific tasks as laid out in the local disaster preparedness plan. The system requirements for running RELSAT are appropriate technical equipment, especially measuring instruments and means of communication, trained operators and test runs. Thus, relative intensive maintenance is required, as well as permanent and reliable coordination and funding.
Source: Relsat n.d.
Of all the natural hazards capable of producing a disaster, a flood is by far the most common in causing loss of life, human suffering, inconvenience and widespread damage to buildings, structures, crops and infrastructure. Importantly, natural hazards are often interrelated, and the occurrence of a given phenomenon may give way to other threatening phenomena in a series of events. For example, seismic activity can create landslides; landslides can create floods, etc.; hurricanes can bring about heavy winds and rains, floods and landslides. Important variables to consider are thus predictability and geographical circumference. Of course, close to an active volcano, for instance, it is easier to convince people to invest in disaster prevention (this has been the experience, e.g., near the Tungurahua volcano in Ecuador). While earthquakes cannot be accurately predicted, extreme weather events can. Whereas short-term flood warnings can be given using rainfall and river-level monitoring, long-term weather prediction remains an inexact art.
In the case of floods inland along rivers and watersheds, the predictability of these events has been much increased following the adoption of technological innovations such as early-warning systems. In a number of Central American countries, one such flood-specific system, RELSAT, was set up (see the Box in this Section). In Honduras, the local RELSAT committee has since promoted dyke construction and reforestation in the middle and upper valley of Masica, and widened evacuation concerns to take into account livestock and not just human beings. Although such hardware is expensive to install, it acted as an important demonstration of political will and as an incentive for setting up and participating actively in the accompanying software (the committee), which achieved much in terms of DRM.
Some other communities had already devised their own early warning system. In Guatemala, towns along the Coyolate River got together in the mid-1990s to map flood-hazard zones, build shelters and monitor river levels. An alarm, triggered by rainfall gauges in the mountains, alerts communities to check river flows and, if necessary, to evacuate. Although 300 people died in floods along other rivers during hurricane Mitch, there was no loss of life along the Coyolate River.