According to the IPCC, climate change will
contribute to coastal flooding. This may be so, but it's certainly not the main
cause. In many of the world's coastal megacities, flooding is the result of the
still ongoing land subsidence, not the sea level rise. Why didn't IPCC
mention this in their latest report on impacts?
The most important factors that contribute to land subsidence are:
·
groundwater
abstraction from aquifers, leading to compaction of overlying soft sediments;
·
surface
drainage for urban development, leading to oxidation of peat and compaction of
top soils.
Other
factors are the winning of oil, natural gas and coal, and postglacial effects.
 |
| Sea level rise (top red line) compared to land subsidence in various cities/area's (source: Deltares) |
Subsidence
occurs in most of world's coastal megacities that usually are situated on thick
clayey delta deposits. Examples of such 'sinking cities' are: Jakarta, Shanghai, Bangkok,
Tianjin, New Orleans, Tokyo, Taipei, Manila, Dhaka, Semarang, etc. In some
cases, cities have sunk by more than five meters during the last century. But
that's not all: the process is still going on, at rates up to 100-200 mm/year.
Compare that to the present sea level rise of only 3 mm/year!
 |
| Jakarta land subsidence in the period 1974-2010. The northern part of the city sinks at a rate of 150-250 mm/year. |
Moreover,
the risk of urban flooding is amplified
by the effects of other human interventions in the upstream catchment.
The
economic damage and other risks - e.g. loss of lives - from land subsidence
will increase rapidly due to population growth, urbanisation and economic
development. It's evident that these problems call for local strategies and
measures.
Without such actions, mitigation efforts to curb the sea level rise is like mopping the floor with the tap wide open.
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Voor meer informatie: zie mijn boek 'Aan de knoppen van het klimaat' Zie ook de recensies van o.a. De Volkskrant en NBD|Biblion.
Without such actions, mitigation efforts to curb the sea level rise is like mopping the floor with the tap wide open.
-------------------------------------------------
Voor meer informatie: zie mijn boek 'Aan de knoppen van het klimaat' Zie ook de recensies van o.a. De Volkskrant en NBD|Biblion.
