STANDARDIZED PRECIPITATION INDEX (SPI) CALCULATED WITH THE USE OF LOG-NORMAL DISTRIBUTION

• Main Authors: Edward Gąsiorek, Elżbieta Musiał, Marian Rojek
• Format: Article
• Language: Polish
• Published: Polish Society of Ecological Engineering (PTIE) 2014-10-01
• Series: Inżynieria Ekologiczna
• Subjects: standardized precipitation index; gamma distribution; normal distribution; log-normal distribution
• Online Access: http://www.journalssystem.com/ie/Wskaznik-standaryzowanego-opadu-spi-wyznaczony-z-zastosowaniem-rozkladu-log-normalnego,244,0,2.html

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.