Xu Jiongxin
This paper deals with the zonal differences in river runoff and human innuence in China,based on the data from 700 river basins.Some regression equations have been established between mean annual runoff and climatic variables such as mean annual precipitation,temperature and aridity index,indicating that precipitation is the major controlling factor of runoff formation from a macroscopic point of view.Therefore,the zonality of runoff is resulted from the zonality of precipitation.Based on data from 700 and 400 river basiins respectively,two curves showing the latitudinal and longitudinal variations in runoff have been established in this study,In the monsoon-influenced eastern China,mean annual runoff decreases from south to north,and reaches the minimum in the zone 36°－40°N;going further into Northeast China,itincreases slightly,The longitudinal variation in runoff is controlled by the joint operation of the east Asian monsoon and the three-stepped macro relief of China,From southeast to northwest,mean annual runoff declines,However,when crossing the bordering zone between the first and the second great steps of macro relief,runoff increases sharply due to the rapidly increased precipitation induced by topographical uplift,and then the runoff declines again.Two sensitive zones are identified from the above two curves, where monitoring stations should be established for the study of regional hydrological response to the global climatic change.Based on 30 representative rivers from different natural zones,the human impact on runoff has been analyzed,showing that the intensity index of human influence Im increases with an increased river basin aridity index;here lm is defined as the difference between the natural and actually measured runoffs divided by the natural runoff.In semiaridzones,mainly the North China,the human impact on river runoff is the strongest,and the water-saving agricultural measures are urgently needed.
