Assessing drought severity is an element of drought monitoring. The severity of drought may be assessed by using various indices as drought criteria. The choice of the criterion affects the result of determining the frequency of dry periods in a given severity class. An analysis of 35-year-long (1970-2004) meteorological records concerning vegetation periods (April-September) and coming from five meteorological stations located in different agro-climatic regions of Poland was used to calculate the standardised precipitation index (SPI) and standardised climatic water balance (KBWs). Within the range of the negative values of SPI and KBWs, four drought classes were distinguished: mild, moderate, severe and extreme. Then, the frequencies of months and vegetation seasons in a given class were established. Using SPI yielded a smaller number of droughts in general than employing KBWs and a smaller number of vegetation periods with drought. Based on SPI, the number of months with extreme and severe drought appeared to be greater compared to KBWs, while the latter index showed more months with moderate and mild drought. Employing an index accounting for meteorological conditions of evaporation (KBWs) softened the judgment on drought severity (periods were shifted to a lower drought class) in comparison with an index based solely on precipitation (SPI).

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