Decline of Yangtze River water and sediment discharge: Impact from natural and anthropogenic changes.

S L Yang,K H Xu,J D Milliman,H F Yang,C S Wu

doi:10.1038/srep12581

Abstract

The increasing impact of both climatic change and human activities on global river systems necessitates an increasing need to identify and quantify the various drivers and their impacts on fluvial water and sediment discharge. Here we show that mean Yangtze River water discharge of the first decade after the closing of the Three Gorges Dam (TGD) (2003–2012) was 67 km3/yr (7%) lower than that of the previous 50 years (1950–2002), and 126 km3/yr less compared to the relatively wet period of pre-TGD decade (1993–2002). Most (60–70%) of the decline can be attributed to decreased precipitation, the remainder resulting from construction of reservoirs, improved water-soil conservation and increased water consumption. Mean sediment flux decreased by 71% between 1950–1968 and the post-TGD decade, about half of which occurred prior to the pre-TGD decade. Approximately 30% of the total decline and 65% of the decline since 2003 can be attributed to the TGD, 5% and 14% of these declines to precipitation change, and the remaining to other dams and soil conservation within the drainage basin. These findings highlight the degree to which changes in riverine water and sediment discharge can be related with multiple environmental and anthropogenic factors.

Highlights

The increasing impact of both climatic change and human activities on global river systems necessitates an increasing need to identify and quantify the various drivers and their impacts on fluvial water and sediment discharge
Over the first decade following the construction of the Three Gorges Dam (TGD) in 2003, the mean annual water discharge from the Yangtze River to the sea was 7% lower than that during the period 1950–2002; the mean sediment flux decreased by 71% relative to 1950–1968 and decreased by 55% compared with 1993–2002
Other reservoirs constructed over the post-TGD decade have a combined storage capacity of 1.5 times larger than the Three Gorges Reservoir (TGR) and were more important in the water discharge decrease

Summary

VIMS Articles

Decline of Yangtze River water and sediment discharge: Impact from natural and anthropogenic changes. Considering the impacts of various aspects, ca.1% of the sediment flux decrease at Datong in the post-TGD decade can be attributed to higher temperature. Within the Minjiang basin, precipitation increased by 3% but water discharge decreased by 2% from the pre- to post-TGD decades. Compared with the period 1950–1968, the mean sediment flux at Datong over the post-TGD decade decreased by 362 Mt/yr (Supplementary Tab. S3, online), 31% of which was attributable to the TGD impact (Fig. 4B). 9% and 5% of the post-TGD decreased water discharges at Datong (relative to 1950–2002 and 1993–2002) to water impoundment and increased evaporation in reservoirs other than the TGR (Fig. 4A). From the pre- to post-TGD decades, sediment flux from the Wujiang River (Fig. 1B) decreased by 14 Mt/yr, which was mainly attributable to several large reservoirs (with a total storage capacity of ca.[13] km). In view of the basin scale of the Yangtze River, these factors are limited to small regional scales, and their comprehensive impacts on the annual water and sediment discharges are probably very minor compared with the impacts of the aforementioned factors

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Additional Information