The direct influence of sea-level rise on water resources This is due to natural subsidence from compaction of
comes principally from: sediment under its own weight and human-induced
new or accelerated erosion of coastal wetlands; subsidence from water extraction and drainage.
more extensive coastal inundation and higher-levels
of sea flooding (see box on the magnitude of impacts Bangladesh consists almost entirely of the densely pop-
from sea-level rise); ulated deltaic plains of the Ganges, Brahmaputra, and
increases in the landward reach of sea waves and Meghna rivers. Here accelerated relative sea-level rise
storm-surges; will likely be further compounded by increasing extreme
seawater intrusion into surface waters and coastal aq- water levels associated with more intense storm surges
uifers (contaminating fresh water); and and monsoon rains. These are in turn related to rising
further encroachment of tidal waters into estuaries water temperatures in the Bay of Bengal. The vulner-
and coastal river systems. ability of Bangladesh is exacerbated by the expansion
of aquaculture, involving the conversion of mangroves
Sea-level rise, on its own, will not result in seawater con- which provide natural coastal defences
53
. Thus sea-level
taminating a fresh groundwater lens – it merely raises rise poses a particular threat to deltaic environments, es-
the height of the interface between the saline and fresh pecially with the synergistic effects of other climate and
water. But frequently, when one or more of the other human pressures
70
.
direct impacts occurs, seawater will penetrate further
into coastal aquifers, including those of small islands. Vulnerability of human settlements and
Higher sea levels will, in most cases, result in a local rise activities
in the water table.
Human settlements and activities are preferentially con-
The distance inland that a water table will be affected centrated close to the coasts of both small islands and
by sea-level rise depends on a range of factors, includ- low-lying areas
71
(Figure 6C.13). This places them at risk
ing elevation and subsurface permeability. In some lo- from high sea levels, be they associated with extreme
cations, particularly in deltas such as those in Bangla- events such as storm surges, or increases over the long-
desh, rising water tables can occur as far as several tens er term
72
. A few examples:
of kilometres inland. Thus, for small islands and even The sustainability of island tourism resorts in Malay-
for depressions that are some distance from the coast, sia is expected to be compromised by rising sea level
sea-level rise may lead to an expansion of the standing causing both beach erosion and saline contamination
body of fresh and brackish water. Drainage and produc- of the coastal wells that are a major source of water
tive use of these and adjacent low-lying areas will often supply for the resorts
73
.
be impeded. The number of annual rice crops possible in the Me-
kong delta will decline dramatically with a relative sea-
Vulnerability of deltas level rise of 20 to 40 cm
74
.
In Hawaii numerous electrical power plants and sub-
Rates of relative sea-level rise can greatly exceed the glo- stations, petroleum and gas storage facilities and life-
bal average in many heavily populated deltaic areas
39
. line infrastructure such as communications, telephone
172 GLOBAL OUTLOOK FOR ICE AND SNOW
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