STANDARDIZED PRECIPITATION INDEX (SPI) CALCULATED WITH THE USE OF LOG-NORMAL DISTRIBUTION
 
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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: 2014-10-17
 
Inż. Ekolog. 2014; 39:62–73
 
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ABSTRACT
The problem analyzed in this paper is the continuation of research conducted on data from Wrocław-Swojec agro- and hydrometeorology observatory in 1964–2009 period and published in “Infrastruktura i Ekologia Terenów Wiejskich” nr 3/III/2012, pp. 197–208. The paper concerns two methods of calculation of standardized precipitation index (SPI). The first one extracts SPI directly from gamma distribution, since monthly precipitation sums in the 1964–2009 period in Wrocław are gamma distributed. The second method is based on the transformations of data leading to normal distribution. The authors calculate SPI with the use of log-normal distribution and confront it with values obtained by gamma and normal distributions. The aim of this paper is to comparatively assess the SPI values obtained with those three different methods.