Evolution and variation characteristics of the recorded runoff for the major rivers in China during 1956—2018

Surface water is a key natural resources and a restrictive element to maintain regional ecological balance and support development of social economy. River runoff is the main form of surface water resources. Variation of the both river runoff and surface water will directly influence water resources management of a basin. Based on the annual report series of water resources and the recorded runoff of 10 representative hydrometric stations on major rivers in China, the variations of the surface water resources of the ten water resources zones and recorded runoff of major rivers in China during 1956—2018 were investigated. The results show that:① The annual runoff gauged on major rivers during 1956—2018 shows a downward trend with exception of the Datong station on the Yangtze River. ② The recorded annual runoff of the Tangnaihai station on the upper Yellow River presented an insignificant decreasing trend while that gauged at the Huayuankou station on the Yellow River exhibited a significant decreasing trend. During 1980—2000 and 2001—2018, the recorded runoff at the Tangnaihai station changed by 1.8% and-5.9% as comparing to baseline in 1956—1979 while that of the Huayuankou station decreased by 26.7% and 41.0% respectively. ③ Geographically, the Yellow River could be treated as separation boundary of runoff variation trends from the north to the south of China in terms of significance level. Recorded annual runoff presented significant decreasing trends for rivers in the north to the Yellow River while that exhibited insignificant variation trends for rivers in its south. The recorded runoff in 2001—2018 decreased by more than 25% relative to the baseline of 1956—1979 for the northern China rivers, with the highest reduction of over-80% occurring in the Haihe River. ④ The average annual surface water resources of China during 1956—2018 was approximately 2 726.6 billion m³, which is 12.2 billion m³ less than that in the second water resources assessment conduced in 2004. Reduction of surface water in the Haihe River zone, Yellow River zone, and Liaohe River zone aggravated contradiction between water supply and water demand since the early 21st century.