Investigation of drought propagation in South Korea using drought index and conditional probability

Meteorological drought commonly originates from precipitation deficit and is then propagated to agricultural and hydrological droughts. Since drought impacts are more directly related to agricultural and hydrological systems of human society, it is important to understand the drought propagation process for reducing drought impacts. This study investigated the propagation of meteorological droughts through the hydrological system in South Korea. We performed comparative analyses between a meteorological drought indicator [Standardized Precipitation Index (SPI) at various timescales] and a hydrological drought indicator [Palmer Hydrological Drought Index (PHDI)], and pooled the mutually dependent drought events from the indicators. The results indicated that most hydrological droughts occurred following meteorological droughts, and drought events became fewer and longer when moving from 3- and 6-month SPI to PHDI. In addition, when we investigated the meteorological conditions, about 70 - 80% of 3- and 6-month SPI corresponding to the onset of hydrological drought (PHDI <= -2) were less than -1.0. We also calculated the propagation probability using the conditional probability theory with 33% (3-month SPI) and 48% (6-month SPI) of meteorological droughts propagated to hydrological drought. We concluded that even though the frequency of hydrological drought in South Korea was less than that of meteorological drought, the severity of hydrological drought was greater than that of meteorological drought.