Human intervention increases risk of delta drowning
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Human intervention increases risk of delta drowning

The world’s deltas are home to over 350
million people. They are fertile environments that support
intensive agriculture and expanding cities as well as unique ecosystems such as the Sundarbans,
the largest mangrove forest in the world. Deltas are created when rivers enter the ocean
and deposit the sediment they carry. This newly created land tends to sink as the
freshly deposited sediment settles and compacts, which means that more sediment must be deposited
for deltas to remain above sea level. Currently many of the world’s deltas are
sinking rapidly relative to sea level as climate change is causing seas to rise, and because
subsurface mining of water and fossil fuels causes rapid subsidence. In these circumstances a sustained supply
of river sediment that promotes continued deposition on delta areas is critically important
in offsetting relative sea level rise. This raises the question we explored in our
paper: how will river sediment delivery to deltas change in the future? To find answers, we used computer modelling
to project changes in fluvial sediment delivery to 47 deltas over the 21st century for a range
of scenarios, which use data on future climate and dam construction as well as population
and wealth as proxies for other human activities. We found that fluvial sediment delivery to
many deltas is expected to decrease under most scenarios due to the influence of human
activities such as dam construction, however the relative influences of different environmental
changes vary between the deltas. Climate change alone is projected to cause
a small increase in sediment delivery to most of the deltas. Anthropogenic activities such as land cover
change, erosion control measures, and river channel engineering are likely to noticeably
reduce sediment delivery to affected deltas. Dam construction in particular is likely to
have a substantial influence, as the effect of existing dams is compounded by further
construction of planned dams. If enough sediment is not retained on then
deltas then, as they sink, salt intrusion, erosion, flooding, and eventually permanent
inundation can threaten the lives and livelihoods of delta inhabitants. The consequences of reductions in fluvial
sediment delivery to deltas provide a clear rational for reducing these impacts. Our research shows that human activities occurring
within river basins are the main driver of change in future sediment delivery. Urgent action is needed to manage rivers to
minimise the disruption of fluvial sediment delivery and improve the resilience and sustainability
of deltas.

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