The assessment of atmospheric drought during vegetation season (according to standardized precipitation index SPI) in central-eastern Poland

The paper presents an assessment of atmospheric drought during vegetation season defined on the basis of standardized precipitation index (SPI). The data used in this paper come from nine IMWM stations from central-eastern region of Poland, and they were registered in 1971–2005. The frequency of occurrence of vegetation season’s months was determined in particular drought classes. Spatial distribution of SPI index values was shown in all of the vegetation season’s months on the area examined. The direction and significance of values changes tendency of the analyzed index during the vegetation season were also defined. It was noticed that extreme droughts appeared four times less frequently than the normal months. Very dry months were noted most frequently in September while moderately dry – in August. The analysis of the frequency of spatial distribution of particular drought classes showed that extreme dry and very dry months occurred most frequently in western part of the area examined, while the moderately dry months also in south-eastern part. On the basis of the linear trend analysis it can be said that the SPI index values were slightly decreasing year by year.