Influence of Three Gorges Dam construction on runoff distribution in the upper reaches of the Yangtze River

Monthly runoff data at Cuntan, Wulong and Yichang stations in the upper reaches of the Yangtze River from 1951-2016, and Copula function were used to analyze quantitatively impact of Three Gorges Reservoir on joint distribution of runoff from multiple stations in the upper reaches of the Yangtze River before and after impoundments. It was found that after construction of the Three Gorges Reservoir, joint distribution of runoff changed at some stations. Joint distribution at Cuntan and Yichang stations did not change, but the parameters of distribution function decreased slightly. Joint distribution at Wulong and Yichang changed from Gaussian Copula to Gumble Copula type. Joint distribution at Cuntan, Wulong and Yichang changed from Gumble Copula to Gaussian Copula type. After construction of the reservoir, runoff at these three stations was significantly reduced at similar probability level. Corresponding runoff at these three stations also decreased significantly in the same return period. Yichang station showed the largest runoff reduction rate, with Cuntan following, with Wulong the smallest. Three Gorges Reservoir therefore impacts runoff at downstream Yichang station higher than upstream Cuntan and Wulong stations.