| The hidden vulnerability of cities to natural disasters: underground spaces
The rapid and extensive underground expansion of mega-cities - for subways, malls, parking and public utilities - takes place often with too little knowledge of associated risks and too few plans to minimise the effects of a natural disaster, United Nations University experts warn. With growing land pressures in cities (which contain about 50 percent of all people today, seen rising to 65 percent by 2030), creating new space underground becomes increasingly attractive. In many places, however, studies of potential natural disaster risks are often neglected, says Srikantha Herath, UNU senior academic programme officer. "The concentration of people and wealth in such underground spaces is expanding and merits careful examination," says Dr. Herath. "Such facilities in many areas have not been used sufficiently long to be exposed to various types of extreme hazard events of low frequencies. Modelling a variety of catastrophic events is essential for building contingencies into underground infrastructure designs, including evacuations and the emergency containment and transport of flood waters, for example." Via underground interconnections, water can travel considerable distances away from the flood source. However, there are often no subsurface maps; underground space is usually mapped in relation to a building overhead. "It is essential to plan and construct underground space based on information such as connectivity, and to design carefully all uncovered entrances to underground spaces," says Janos Bogardi, director of UNU's new Institute for Environment and Human Security (EHS) in Bonn. "At the same time, underground spaces should be designed to withstand multi-hazards. For example, fire risks require planners to also include the ability to seal off and compartmentalise underground space quickly." Underground disasters can also pose dangers to those in buildings overhead, he adds. Floor utility spaces in multi-story underground structures cannot hold large amounts of water and may collapse floors below. Ventilation ducts may also be compromised. "The frequency of underground flooding events is surprisingly high in places," says Dr. Herath. Tokyo records, for example, show 17 incidents from 1999 to 2001, some involving fatalities despite extensive precautions. Most floods occurred in the rain and typhoon months, July to September. Many such coastal mega-cities are vulnerable to flood events given a terrible combination of conditions, such as a heavy rainfall combined with tides or sea surges caused by winds or earthquake. Global warming is predicted to make extreme rain events more frequent, he added. The hidden vulnerability of mega-cities will be among topics under review by international experts at the World Conference on Disaster Reduction, being held between January 18th-22nd in Kobe, Japan to mark the 10th anniversary of that city's devastating earthquake.
•Date:
14th January 2005 • Region: World •Type:
Article •Topic:
BC facilities |
