Spatial and temporal variation of runoff in the Yangtze River basin during the past 40 years

Frequent floods occur in the Yangtze River basin, where the Three Gorges reservoir has been constructed. However, in recent years, it has been found that droughts have also occurred frequently. For a better understanding of the spatial and temporal variations in runoff in the Yangtze River basin, especially in the upper Three Gorges reservoir area during the past 40 years, a hydro-climate data analysis was carried out together with rainfall-runoff modeling. The trends in precipitation and river discharge were analyzed for the whole Yangtze River basin, offering a comparison upstream and downstream of the Three Gorges Dam. The results showed that both precipitation and discharge along the downstream of the dam had statistically significant increasing trends in summer. However, the upstream area had significant decreasing trends for both precipitation and discharge in autumn. To analyze the spatial-temporal variation of runoff in the upper Yangtze River, a geomorphology-based distributed hydrological model (GBHM) was used for simulating the natural runoff during 1961–2000. It was confirmed that the natural runoff increased in summer and decreased greatly in autumn. This natural change in runoff in the upper Yangtze River basin implies an increasing flood risk in summer and water shortage in autumn.