Decreasing or increasing trends? Evidence of long-term change in river discharge over the northern Korean Peninsula, 1951–2010

In this study, the trends in river discharge were investigated on different time scales for the period 1951/52–2009/10 over the northern part of the Korean peninsula based on the reliable flow datasets measured at the stations with near-natural states, and no or less anthropogenic activities. The annual mean discharge decreased by 5–11%/decade and its abrupt years appeared around 1980. On the seasonal scale, the trends in the rainy season were the most definitely observed with the decreasing rate of 6–12%/decade and could be seen to begin earlier than the annual trends. Unlike the annual and seasonal trends, the monthly trends exhibited very fluctuant variations depending on the individual months and locations. Overall, considering the detected significant trends, there is strong evidence that the river discharge remarkably decreased with the enhanced variability and the decreasing trends were a predominant part of the changes in the river discharge in the study period. With regard to the hydrological regions, the result suggested that the river discharge in the coastal hydrological regions influenced by the oceanic climate could be more sensitive to climate change than in the northern inland area with the continental climate.