Natural Hazards: Causes and Effects - Disaster Management Center ...
Share Embed Flag
Download ePaper

Natural Hazards: Causes and Effects - Disaster Management Center ...

Natural Hazards: Causes and Effects - Disaster Management Center ... Natural Hazards: Causes and Effects - Disaster Management Center ...

dmc.engr.wisc.edu
from dmc.engr.wisc.edu More from this publisher
05.01.2013 Views

center is about 175 kilometers (110 miles). The probable error appears to be directly related to the forecast period; for example, the average error of a 48-hour forecast is about twice that of a 24-hour forecast. Errors in forecasting the position of the center of a tropical cyclone are, of course, of immense practical importance. It is therefore encouraging that the verification statistics show an improving trend, a sign that additional data and intensive research are beginning to yield dividends. Forecasting Flooding In the forecasting and warning aspects of flood risk, there must be close coordination between the meteorological forecasters and the hydrologists who will be working with the water authorities and local officials. The meteorologist, besides forecasting the intensity, movement and evolution of the tropical cyclone, will also prepare forecasts of rainfall, its time of onset, duration and the amounts expected. Rainfall is nearly always heavy in a tropical cyclone and may amount to a total between 75 and 300 millimeters during a period lasting from 12 to 48 hours. The rainfall varies considerably from one storm to another and is strongly influenced by the time required for the cyclone to pass. In mountainous countries the rainfall can be extremely heavy. For example, Japanese and Chinese weather records frequently show more than 600 millimeters of rain falling during the passage of a typhoon over large areas in the mountains. The assessment of flood risks is based primarily on rainfall forecasts in those areas where the time interval between heavy rain and a flood is apt to be short. Examples of such areas are a city that is within the vicinity of a watershed and a small island that has mountains in the interior. In other areas where the water flows downstream for many hours or several days before doing any damage, flood forecasting is based mainly on an analysis of successive measurements of stream flow at various points along a river. Other important factors include the accumulated total of rain that has already fallen and the actual state of the rivers in relation to flood levels. Forecasting Storm Surges The forecasting of storm surges is at present largely based on empirical methods. Much promising research is now in progress in several countries. The object is to develop dynamic models that will provide numerical predictions to supplement those based on empirical formulae. One important preparatory step in the forecasting of storm surges consists of having available a considerable amount of background information. Among the items required are frequency charts of strong winds, the range of the diurnal tide for the months of the storm season, and the results of surveys of the topography of the continental shelf and of bays along the coast. 11 Warning Systems Warning systems should be viewed as a combination of technical and social arrangements that allow individuals and groups affected by a storm to respond in ways most beneficial to them. On the technical side there needs to be a complex evaluation of meteorological data plus knowledge of coastal factors and engineering works that may modify the effects of the storm. On the social side the conditions for effective operation include organization for action to take place when the warning is received, issuance of the warning, directions for action transmitted as part of the warning, and evacuation where required. Assumptions often made about warning systems are that the message is not changed in transmission, that the recipients will understand it as intended by those who issued it, and that

Storm Surge Source: Cuny, Disasters and Development, Oxford University Press, New York, 1983, page 33 Figure 5.3

Storm Surge<br />

Source: Cuny, <strong>Disaster</strong>s <strong>and</strong> Development, Oxford University Press, New York, 1983, page 33<br />

Figure 5.3

logo

products

Resources

Company

Terms of service
Privacy policy
Cookie policy
Cookie settings
Imprint
Change language
Made with love in Switzerland
© 2024 Yumpu.com all rights reserved

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!