Drought in the Bulgarian low regions during the 20th century

In this study, the long-term variations in precipitation in the Bulgarian low regions: the Danube Plain in north Bulgaria and the Thracian Lowland in south Bulgaria, were analysed. Some quantitative criteria were also used to compare drought frequency and intensity between the two regions and between different years. Analyses of the rainy conditions in the selected regions during the 20th century were carried out. The last century can be split into several wet and dry sub-periods with duration of 10-15 years. The long-term variations of the Ped and PAI drought indices are also considered in the paper. In addition, the drought conditions in the Danube Plain and the Thracian Lowland were estimated using the de Marton aridity index. The results obtained show that the latter index can also be applied for the detection of drought periods in the regions considered.