the comparison of standardized precipitation index (spi), standardized reference evapotranspiration index (sei) and standardized climatic water balance (scwb)

The standardized precipitation index (SPI), standardized reference evapotranspiration index (SEI) and standardized climatic water balance (SCWB) were used to analyze the humidity conditions in the vegetation period of years 1964–2006 in Wrocław-Swojec Observatory. SPI and SEI were calculated on the assumption that empirical monthly precipitation sums and monthly sums of reference evapotraspiration, obtained from Wrocław-Swojec data, are gamma distributed. Since monthly sums of climatic water balance for analogous data are normally distributed, CWB required standardization to SCWB. The aim of study was to compare those three indexes: standardized precipitation index (SPI), standardized reference evapotranspiration index (SEI) and standardized climatic water balance (SCWB).