Increase in the hydrological drought risk in different geographical regions of Poland in the 20th century

The purpose of this study was to evaluate the growing threat of hydrological droughts for the territory of Poland. Using the values of the Palmer Drought Severity Index (PDSI) tendencies in the appearance of drought months were analyzed in summer months in the 20th century. An increase in the frequency of appearance of drought months was detected in last two decades. Monthly minimum values of the PDSI show statistically significant downward tendency which indicates tendency towards over drying. Mean values of the PDSI for the period 1991-2000 was significantly lower then values in the reference period 1961-1990 for the most of the territory of Poland