Towards the Understanding of Recent Lake Decline in the Yangtze Basin

Abstract:

In the era of Anthropocene, lakes as essential stocks of terrestrial water resources are subject to increasing vulnerability from both climatic variations and human activities. Our recent study reveals a decadal area decline among the largest cluster of freshwater lakes in East Asia, distributed across the Yangtze River Basin downstream of China’s Three Gorges Dam (TGD). The observed lake decline, a cumulative rate of 7.4% (~850 km²) from 2000 to 2011, concurred with enduring meteorological drought, continuous population growth, and extensive human water regulation (e.g., the TGD). The decreasing trend was tested significant in all seasons, leading to an evident phase drop of the average annual lake cycle before and after the TGD operation. The most substantial decline in the post-TGD period appears in fall (1.1% yr^-1), which intriguingly coincides with the TGD water storage season. Motivated by such findings, this paper provides a comprehensive diagnosis of the potential TGD impacts on the Yangtze-connected downstream lake system, in comparison to the concurrent contributions from local meteorological variations and human water consumption. Results uncover an altered inundation regime of the downstream lake system induced by TGD’s water regulation, manifested as evident lake area decrease in fall and increase in spring and winter. As the most substantial influence, reduced lake area in fall explains ~20–80% of the observed post-TGD decline. Concurrent Yangtze channel erosion slightly reinforced the area decrease in fall while counteracting ~30% of the area increase in winter. Human water consumption accumulated through the local river network led to constant discharge reduction, which equals another ~80% of the TGD-induced lake decline in fall and completely counteracts the TGD-induced lake area increase in winter. However, human water consumption only adds minor contribution (< 6%) to the post-TGD lake decline due to slow increasing rates during 2000–2011. The major proportions of seasonal post-TGD lake declines were tested to be largely triggered by the decadal climatic drought across the downstream Yangtze Basin; however, the quantified anthropogenic impacts are evident and anticipated to increase in the coming decades due to chronic Yangtze channel erosion and continuous growth of human water demand.