Natural disasters - risk assessment and response

Context

In 1990 the United Nations launched in the International Decade for Natural Disaster Reduction to "reduce through concerted international action, especially in developing countries, the loss of life, property damage, and social and economic disruption caused by natural disasters".

Globally, damage inflicted by natural disasters kills an estimated one million people each decade and leaves millions more homeless. Events such as floods, tropical storms and droughts account for most of the damage. The economic effects of these natural disasters has tripled in the last thirty years; during the decade 1980 to 1989, the cost was 94 billion ECU, of which only 0.8 billion ECU was incurred before 1987.

Contents

There are many different types and levels of severity of natural disasters, many of which can be detected and monitored from satellites, including ERS. The particular applications covered here are:

• Surface movement monitoring: Earthquakes and landslides
• Monitoring and response to floods
• Volcano monitoring

Many hazards exist in the marine environment, such as that danger presented to shipping in ice-infested seas, or the threats posed by high waves and winds to a variety of marine activities. More information can be found in Hazards & Risks in the Marine Environment. Monitoring of oil spills is discussed in Coastal Zone Monitoring & Management.

Surface movement monitoring

Surface rupture of Highway 247 caused by the Landers Earthquake

The ability of differential SAR interferometry to detect and quantify extremely small surface height variations or topographical surface movements, such as those that occur before an earthquake has been demonstrated over the past few years by numerous studies carried out within the framework of natural hazards research programs.This technique can also be used to monitor subsidence associated with mining or water/hydrocarbon extraction. To make such information useful to decision makers with no knowledge of the technique, the information can be incorporated into Geographic Information Systems (GIS), along with other complementary data sources. These systems can then be placed into earthquake prone regions, for example, to assist in the management of associated risks.

Flood Monitoring

Extensive flooding near Oxford, UK. (Courtesy Institute of Hydrology, UK)

In the five years between 1988 and 1992, there were twenty-three flood events that caused damage in excess of 1% of the Gross National Product in the country in question, and fifty-one events in which more than one hundred people died. Prevention and preparedness measures can make a difference.

ERS SAR products can be used in the event of flooding to permit immediate assessments of the areas at risk and aid decision-making on relief and clean-up operations. Products derived from archived SAR data may provide accurate spatial information on the extent of previous flood events. This is being used for management planning for preventative measures in areas where flooding occurs regularly. ERS SAR can serve as up-to-date information in the absence of conventional optical satellite or other data. This is often the case in bad weather conditions which accompany flooding events.

Volcano monitoring

Lahar depositing

About ten percent of the world's population live near an active volcano, and that figure is expected to rise. In the next four years more than 100 of the world's cities will have populations of more than two million and half of those will be close to tectonic plates. It is widely believed that a huge volcanic eruption, of which only two occur every 100000 years, is long overdue. During the UN-sponsored International Decade for Disaster Reduction, 18 volcanoes have been selected for special study, but there are at least 600 more which are or may become active.

In this context, monitoring and response initiatives are of paramount importance. Experts in volcanology are calling for more volcanoes to be monitored - at present only one in five is. Through the use of SAR imagery it is possible to detect both the small surface movements which may herald a volcanic eruption, and to monitor the aftermath, lahar depositing being the example shown in the figure. A recent example is the application of multitemporal SAR analysis and SAR interferometry to the Vatnajokull volcano, which erupted in October 1996.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry