Drought in the Lower Danube

Bulgaria is situated on the Balkan Peninsula. Its northern frontier is the lower part of the Danube. The Balkan range, with its zonal situation, is part of a natural climatic frontier, dividing Bulgaria into two parts—north and south. One of the main features of the climate in the Danube Plain (northern Bulgaria) is insufficient precipitation—a tendency toward dryness and frequent droughts. The annual amount of precipitation is 500–600 mm. The highest monthly values are measured in June (in some places in May), with 55–75 mm. February (in some places, March) is the driest month. Absence of precipitation can occur in any month, but the probability of this happening in May and June is very low. At the same time, monthly precipitation can exceed 100 mm in any month; in the summer it can even exceed 250–300 mm. The radiation balance is about 50 Kkal.sm-2. In this study, Budyko’s dryness ratio (1985) is used to define land moistening