ASSESSMENT OF ACCURACY OF PRECIPITATION INDEX (SPI) DETERMI-NED BY DIFFERENT PROBABILITY DISTRIBUTIONS
 
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1
Katedra Matematyki, Uniwersytet Przyrodniczy we Wrocławiu, ul. Grunwaldzka 53, 50-357 Wrocław
2
Instytut Kształtowania i Ochrony Środowiska, Uniwersytet Przyrodniczy we Wrocławiu
Publication date: 2014-11-04
 
Inż. Ekolog. 2014; 40:92–99
 
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ABSTRACT
The use of different calculating methods to compute the standardized precipitation index (SPI) results in various approximations. Methods based on normal distribution and its transformations, as well as on gamma distribution, give similar results and may be used equally, whereas the lognormal distribution fitting method is significantly discrepant, especially for extreme values of SPI. Therefore, it is problematic which method gives the distribution optimally fitted to empirical data. The aim of this study is to categorize the above mentioned methods according to the degree of approximation to empirical data from the Observatory of Agro- and Hydrometeorology in Wrocław-Swojec from 1964–2009 years.