Abstract
The world’s large rivers are under stress and experiencing unprecedented changes in hydrology, ecosystems, and fluvial sediment loads. Many of these rivers terminate at the great deltas of the world (home to 500 million people), which depend on fluvial sediments for their very existence. While fluvial sediment loads of large rivers have already been greatly modified by human activities, climate change is expected to further exacerbate the situation. But how does the effect of climate change on fluvial sediment loads compare with that of human impacts? Here, we address this question by combining historical observations and 21st century projections for one of the world’s largest 25 rivers containing two mega dams; Pearl River, China. Our analysis shows that variations in fluvial sediment supply to the coast from the Pearl river over a ~150 year study period are dominated by human activities. Projected climate change driven 21st century increases in riverflow will only compensate for about 1% of the human induced deficit in sediment load, leading to the coastal zone being starved of about 6000 Mt of sediment over the remainder of this century. A similar dominance of human impacts on fluvial sediment supply is likely at other heavily engineered rivers.
Highlights
The flood plains and the deltaic coastal zones of the world’s large rivers, inhabited by some 2.7 billion people, have historically been the cornerstone of human civilization[1,2,3,4,5,6]
We take a step towards addressing this knowledge gap by combining historical observations and 21st century projections to quantify the relative contributions from both human impacts and climate change to the fluvial sediment supplied to the coast by the Pearl River, China over a ~150 year period
Any significant departure from the natural fluvial sediment supply is very likely to result in sustained erosion leading to large scale coastal zone land losses
Summary
With the strategic use of historical data and future projections, this study derived quantitative insights into the relative impacts of human activities and climate change on variations in fluvial sediment supply to the coast at the globally relevant Pearl River, China, over a ~150 year period (1954–2100). This analysis showed that the fluvial sediment supply to the coast from the Pearl river has decreased (from its natural state) by 71% from 1954–2013 due to human activities, and that projected increases in riverflow due to climate change will compensate for just 1% of this deficit by the end of the 21st century (if the impact of human activities is maintained at current levels) Based on these projections, the coastal zone of the Pearl River will be starved of approximately 6,000 Mt of fluvial sediment during the remainder of the 21st century. Large human induced deficit in fluvial sediment supply to the coast, such as that projected here for the Pearl River, when considering the coastal zone sediment budget could lead to sub-optimal designs and decisions, which may, under some circumstances, place coastal settlements and communities at risk
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