With the impact of climate change and increasing the intensity of human activities,the hydrological regime has changed,including annual runoff distribution,which is relating with water resources management and ecological construction.In this paper,the index of unevenness,concentration,and variation have been defined and calculated according to gauge records of runoff in the 1956-2000.Then the change of annual runoff distribution in the headwaters of the Yangtze River is discussed.It is revealed that: 1) the...