Newsletter

02 | 2006


Natural hazards more common than currently estimated

Interpretation methods of statistics distort conclusions

According to a VTT study, natural hazards, such as hurricanes, floods, earthquakes and snow storms, actually occur more often than the statistics indicate. The underestimation of the risks related to extraordinary phenomena makes it difficult for society to prepare for natural hazards.

Senior Research Scientist Docent Lasse Makkonen's analysis regarding the frequency of uncommon phenomena was published in the latest issue of the Journal of Applied Meteorology and Climatology, published by the American Meteorological Society.

The frequency of very unusual natural phenomena has for some 50 years been evaluated by means of the statistical analysis of extreme phenomena, the so-called extreme value analysis. For this, it is necessary to evaluate the probability of the most serious case that has ever been observed. In his article, Makkonen shows that in the commonly used extreme value analysis methods the probabilities are incorrectly linked to the perceptions.

As an example, a phenomenon that occurs once in every 50 years on average is estimated by the current methods to occur more rarely, only once in every 100 years.

The errors are reflected in the building codes as well, as the dimensioning of the structures is based on the evaluation of the probability of phenomena causing damage. 

According to Makkonen, incorrect methods of describing the risks related to uncommon phenomena appear in numerous books, commercial software and engineering handbooks, which makes it difficult for societies to prepare for natural hazards.

 


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