Abstract:

This paper aims to investigate the climatic and anthropogenic impacts on the Yangtze River water discharge over the last six decades. We analyzed the time series of annual temperature, precipitation, evaporation and water discharge, employing the means of MannKendall and regression methods, in combination with data of reservoir construction, water consuming, and water and soil conservation. The results are as follows. (1) From 1956 to 2011, the catchmentaveraged annual temperature significantly increased, at a rate greater than the level of global average. (2) No significant trend was found for the catchmentaveraged annual precipitation, and therefore the annual precipitation was not well related to the annual temperature. (3) No significant trend was found for the catchmentwide actual evaporation (i.e. the difference between precipitation and runoff), although a significant decreasing trend was found for the catchmentwide annual pan evaporation. (4) Interannual changes in annual precipitation and water discharge were frequent and significant. For the whole Yangtze River Basin, the maximum annual precipitation was 1.4 times greater than the minimum annual precipitation, and the maximum annual discharge was 1.9 times greater than the minimum annual discharge. The correlation between annual precipitation and water discharge was very significant (R2 = 0.78). (5) No statistically significant trend was found for the annual water discharge of the Yangtze River, although the water discharge decreased by 3% from the initial decade (1956-1965) to the recent decade (2002-2011). (6) Spatial changes in climatic and anthropogenic impacts on water discharge were found within the Yangtze River Basin. A significant decreasing trend in annual water discharge was found for the North Area (Minjiang, Jialingjiang and Hanjiang tributaries), and a significant increasing trend in annual water discharge was found for the Centre Area (the “ungauged area” along the main river below the Jinshajiang), whereas no significance was found for the other subareas. Compared with the initial decade, the water discharge of the recent decade decreased by 14% in the North Area and decreased by 4% in the West Area, whereas it increased by 7% in the Central Area. The significant decreasing trend in water discharge in the North Area was attributable mainly to human activities (e.g. watersoil conservation projects and reservoir construction). On the other hand, the significant increasing trend in water discharge in the Centre Area was most probably due to the decrease in evaporation which was presumed attributed to decreases in net solar radiation and wind speed. These two aspects of influencing factors, anthropogenic and climatic, have opposite effect on actual evaporation, and therefore offset each other in affecting the whole Yangtze River water discharge. This study suggests that anthropogenic and climatic impacts on water discharge, even though they could be separately significant, could cancel each other in some rivers and during some periods. We predict that human activities will be the dominant factor influencing the water discharge in the Yangtze River in the coming decades. Under the influences of the South to North Water Diversion, construction of new reservoirs, increasing water consuming and watersoil conservation, the decadal water discharge will probably decrease by 10% by the end of this century, compared with the present level