The small, intense depressions of tropical latitudes are called tropical cyclones (or typhoons or hurricanes, depending on the region in which they occur). A tropical cyclone forms over the open sea and usually moves towards land on reaching which it either moves into the interior or travels along the coastline. A large area, perhaps several countries, may be affected by a tropical cyclone during its active existence of several weeks, and the toll in terms of loss of life, material damage and economic losses may be extremely heavy, even to the extent of cancelling economic growth over a period of years*. In the North West Pacific more than 30 tropical cyclones may be expected to develop each year. In other regions the frequency is usually lower. The fundamental characteristics of tropical cyclones are: (i) Frequency of occurrence, intensity, speed and direction of movement, etc.; (ii) Wind and rainfall distribution; {iii) Storm surges - frequency/height distribution, and relationship to meteorological parameters. The hydrological component of tropical cyclones is concerned mainly with the following subjects: (i) Hydrometeorological aspects of tropical cyclone rainfall - depth/duration/frequency relationships; (ii) Use of hydrological models for estimating probabilities of flood river discharges associ- ated with rainfall of given characteristics. *Techniques for the assessment of natural hazard are described in some detail in Special Environmental Report No. 8: The Quantitative Evaluation of the Risk of Disaster from Tropical Cyclones, 1976. Secretariat of the World Meteorological Organization, Geneva, Sales No. 455, English/French/Spanish, 143 pages, Price SO SFr. ISBN 92 - 63 - 10455 -7. 5.2 Tornadoes A number of dangerous meteorological phenomena - tornadoes, thunderstorms, lightning and hail - are conveniently classified within the description “severe local storms”. These storms have a relatively short life cycle and affect small areas rather than large regions. Although any 
**Analysis**
The text discusses natural disasters, specifically tropical cyclones, and their impact on the environment, human life, and economy. It seems to be more focused on the scientific aspects of tropical cyclones, their characteristics, and the effects they have on the environment and human activities.

**Category**
Natural resources and environment, Science and technology