Abstract: From the view of water cycling, runoff coefficients are important index of water resoureces in a particular catchment. The changes of runoff coefficents in the five rivers of Poyang Lake basins during 1955-2002 were analysed. And the corresponding relationship between the changes of climate factors and runoff coefficients is the emphasis question discussed. Results show that runoff coefficients of the Poyang River basin increased significantly and changed abruptly in the late 1960s and the early 1990s. The trends and abrupt changes of runoff coefficients are in accordance with that of precipitation,evapotranspiration and temprature, respectively, especially with the precipitation. As for seasonal changes, runoff coefficients corresponded well to the climate change from July to September in 1955-2002. This suggests that climate factors significantly influenced the changes of runoff coefficients. Although the runoff coefficients would also be impacted by soil erosion and topographic condition, climate factors are still the main factors to the changes of runoff coefficients.

Key words: runoff coefficient, climate change, abrupt change, Poyang Lake basin