BALWOIS 2004 Ohrid, Macedonia, 25-29 May 2004   DROUGHT PERIODS DURING XXTH CENTURY   Ekaterina Koleva, Vesselin Alexandrov, Nikola Slavov National Institute of Meteorology and Hydrology Tzarigradsko shosse, 66 Sofia, BULGARIA Ekaterina.Koleva@meteo.bg The drought problem always exists somewhere in the world so that the economy of some nation or nations is always being adversely […]