Environmental Engineering Reference
In-Depth Information
simulating current hydrological events, and with
further development it should be able to provide
a more accurate representation of regional
hydrology following global warming than is
currently possible. Beyond such studies, the
general lack of attention to the hydrologic cycle
following global warming is an important gap
in current research.
One aspect of global hydrology which has
been considered in some detail is the impact of
higher world temperatures on sea level. Warming
would cause sea level to rise as a result of the
thermal expansion of sea water and the return
of additional water to the oceans from melting
temperate glaciers. Global mean sea level has
already been rising by about 1.5 cm per decade
over the past century, and with global warming
that rate is likely to accelerate to between 3-10
cm per decade (Hengeveld 1991). The IPCC has
estimated that by 2030 sea level will be 18 cm
higher than at present, and by 2070 the rise will
be 44 cm (Warrick and Oerlemans 1990). Earlier
studies indicated that mean sea level might rise
by as much as a metre as early as 2050 (Titus
1986), but the IPCC assessment does not foresee
a rise of that amount during the next century
(Warrick and Oerlemans 1990).
Although such increases are relatively minor
compared to past changes in sea level, they
would be sufficient to cause serious flooding
and erosion in coastal areas. In low lying
regions such as the Netherlands already
dependent upon major protective works, even a
sea level rise of half that postulated would have
major consequences (Hekstra 1986). Land close
to sea level in Britain—around the Wash, for
example—would be similarly vulnerable, and
structures like the Thames Flood Barrier might
be needed on other British rivers. Environment
Canada has commissioned studies of the impact
of sea level rises in the Maritime Provinces,
which show that flooding events or storm
surges would become more frequent and severe,
presenting serious problems for sewage and
industrial waste facilities, road and rail systems
and harbour activities (Martex Ltd. 1987;
Stokoe 1988).
A sea level rise of little more than 20 cm
would place some 1.1 m hectares in jeopardy
along the east coast of China, from the Pearl
River in the south to Bohai Bay in the north
(NCGCC 1990). In Bangladesh, more than
100,000 hectares would be inundated by a 50
cm rise in sea level (Mackay and Hengeveld
1990), causing the loss of good agricultural
land and displacing tens of thousands of people.
Some of the island nations in the Pacific and
Indian Oceans would face even more serious
problems. The highest point on the Maldive
Islands in the Indian Ocean, for example, is
only 6 m above present sea level (Hengeveld
1991), and the average elevation of the
Marshall Islands in the west central Pacific is
less than 3 m (Climate Institute 1992a). Both
areas are already being threatened by flooding
and increased coastal erosion, and if sea level
continues to rise they will become
uninhabitable.
The impact of even small rises in sea level is
increased during high tides or storms, and when
the two combine the results can be disastrous.
In 1953, for example, high tides and a storm
surge in the North Sea led to major flooding in
eastern England, Belgium and the Netherlands.
Over 2,000 people drowned. At that time, such
an event was to be expected no more than once
in 150 years. Since then, with rising sea levels,
the odds have shortened to once in 35 years,
despite the development of better coastal
defences (Simons 1992).
Whether storminess would increase or
decrease in a warmer world remains a matter of
controversy. In mid-latitudes, the storms that
develop in the North Atlantic and Pacific and
across the southern oceans, are driven by a strong
latitudinal temperature gradient. With the rising
temperatures projected for higher latitudes, that
gradient would be reduced, and mid-latitude
storminess might therefore be expected to decline
(Houghton
et al.
1990). It is possible, however,
that those storms that do develop will be more
intense, fuelled by greater evaporation rates over
a warmer ocean, and the consequent increase in
the energy flux between ocean and atmosphere.
