Climatological characteristics and long-term variation of rainy season and torrential rain over DPR Korea

Abstract Understanding extreme precipitation variability in Democratic People's Republic of Korea (DPRK) is important for monitoring and predicting droughts and floods, which is crucial for agricultural activities and water resources management in the country. Observed daily (hourly) precipitation data from 181 stations in DPR Korea during 1960–2007 (1969–2007) was used to analyze the onset, retreat and length of the rainy season (called Jangma in DPRK, Changma in South Korea, and Meiyu in the Yangtze basin of China), and to examine the climatological features and long-term change of torrential rains. The results showed: (1) The Onset, Retreat and Length of Rainy Season (O-RS, R-RS and L-RS) experienced an obvious inter annual and decadalvariability, and they also had a good correlation with El Nino ( La Nina), with some differences from those found in South Korea; (2) The linear trend of O-RS was 1.9day/ decadeduring 1960–2007, indicating a gradually delayed O-RS, and the R-RS were getting earlier with a rate of −2.7day/ decade, leading to a shortening L-RS at a rate of −4.7day/ decade; (3) Regional differences of the numbers of Torrential Rain(TR) were obvious, which was related to the orographic effect, with the south and northwest of the study area registering the most frequent TR events; We also found that the frequency, intensity and amount of annual TR events generallyincreased during the last 4 decades; (4) The annual number of TR events with amount of precipitation more than 100 mm/6 h increased from 4.2 times (1974–1983) to 7.4 times (2003–2012), and the annual number of extremely intense TR more than 200mm/12 h also increased from 0.6 times to 1.2 times over the same two time periods.