当自然变异对人类生存及其环境和物质财富带来严重危害时就构成了灾害。人口的高速膨胀和经济的集中发展也同样衍生了灾害。过去的二十年里,突发性灾害已在世界范围内造成280万人死亡,直接经济损失达250—1000亿美元。我国近40年来,平均每年因自然灾害造成数万人死亡,直接经济损失高达 Natural disasters create disasters when they cause serious harm to human existence and its environment and material wealth. The rapid expansion of the population and the concentrated development of the economy have also brought about a disaster. In the past two decades, a sudden disaster has killed 2.8 million people worldwide and has a direct economic loss of 25-100 billion U.S. dollars. In the recent 40 years of our country, tens of thousands of people have died as a result of natural disasters every year on average, up to the direct economic losses