72
Table 5.5. SRES scenario Source: United Nations – IPCC
Current sea level rise has occurred at a mean rate of 1.8 mm per year for the past century, and more recently at rates estimated near 2.8 ± 0.4 to 3.1 ± 0.7mm per year 1993-2003. Current
sea level rise is due partly to human-induced
global warming
, which will increase sea level over the coming century and longer periods. Increasing temperatures result in sea level rise
by the
thermal expansion
of water and through the addition of water to the oceans from the melting of continental
ice sheets
. Thermal expansion, which is well-quantified, is currently the primary contributor to sea level rise and is expected to be the primary contributor over the
course of the next century. Glacial contributions to sea-level rise are less important, and are more difficult to predict and quantify. Values for predicted sea level rise over the course of
the next century typically range from 90 to 880 mm, with a central value of 480 mm. Based on an analog to the deglaciation of North America at 9,000 years before present, some
scientists predict sea level rise of 1.3 meters in the next century. However, models of glacial flow in the smaller present-day ice sheets show that a probable maximum value for sea level
rise in the next century is 80 centimeters, based on limitations on how quickly ice can flow below the
equilibrium line altitude
and to the sea.
5.3.1
Future sea level rise
In 2007, the
Intergovernmental Panel on Climate Change
s
Fourth Assessment Report
predicted that by 2100,
global warming
will lead to a sea level rise of 19 to 58 cm, depending on which of six possible world scenarios comes to pass.
These sea level rises could lead to difficulties for shore-based communities in the next centuries: for example, many major cities such as London and
New Orleans
already need storm-surge defenses, and would need more if sea level rose, though they also face issues
The four SRES
scenario families of the Fourth Assessment Report vs. projected global average surface warming until 2100
more economic focus more environmental focus
Globalisation homogeneous world
A1
rapid economic growth groups: A1T; A1B; A1Fl
1.4 - 6.4 °C B1
global environmental sustainability
1.1 - 2.9 °C
Regionalisation heterogeneous world
A2
regionally oriented economic development
2.0 - 5.4 °C B2
local environmental sustainability
1.4 - 3.8 °C
73 such as sinking land. Sea level rise could also displace many shore-based populations: for
example it is estimated that a sea level rise of just 20 cm could create 740,000 homeless people in Nigeria.
Future sea level rise, like the recent rise, is not expected to be globally uniform details below. Some regions show a sea-level rise substantially more than the global average in many cases of more than
twice the average, and others a sea level fall. However, models disagree as to the likely pattern of sea level change.
5.3.2
Effects of sea level rise
Based on the projected increases stated above, the IPCC TAR WG II report notes that current and future climate change would be expected to have a number of impacts, particularly on
coastal systems. Such impacts may include increased
coastal erosion
, higher storm-surge flooding, inhibition of
primary production
processes, more extensive coastal inundation, changes in surface
water quality
and groundwater characteristics, increased loss of property and coastal
habitats
, increased flood risk and potential loss of life, loss of nonmonetary
cultural
resources and values, impacts on
agriculture
and
aquaculture
through decline in
soil
and water quality, and loss of
tourism
,
recreation
, and
transportation
functions. There is an implication that many of these impacts will be detrimental—especially for the
three-quarters of the worlds poor who depend on agriculture systems. The report does, however, note that owing to the great diversity of coastal environments; regional and local
differences in projected relative sea level and climate changes; and differences in the resilience and adaptive capacity of
ecosystems
, sectors, and countries, the impacts will be highly variable in time and space.
Statistical data on the human impact of sea level rise is scarce. A study in the April, 2007 issue of Environment and Urbanization reports that 634 million people live in coastal areas
within 30 feet 9.1 m of sea level. The study also reported that about two thirds of the worlds
cities
with over five million people are located in these low-lying coastal areas. The IPCC report of 2007 estimated that accelerated melting of the Himalayan ice caps and the
resulting rise in sea levels would likely increase the severity of flooding in the short-term during the rainy season and greatly magnify the impact of tidal storm surges during the
cyclone season. A sea-level rise of just 40 cm in the Bay of Bengal would put 11 percent of the countrys coastal land underwater, creating 7 to 10 million climate refugees.
IPCC assessments suggest that deltas and small
island
states are particularly vulnerable to sea level rise caused by both thermal expansion and ocean volume. Relative sea level rise mostly
caused by
subsidence
is currently causing substantial loss of lands in some deltas. Sea level changes have not yet been conclusively proven to have directly resulted in environmental,
humanitarian, or economic losses to small island states, but the IPCC and other bodies have found this a serious risk scenario in coming decades.
Coastal wetland ecosystems, such as salt marshes and mangroves are particularly vulnerable to rising sea level because they are generally within a few feet of sea level
IPCC, 2007
.
Wetlands
provide habitat for many species, play a key role in nutrient uptake, serve as the
74 basis for many communities’ economic livelihoods, provide recreational opportunities, and
protect local areas from flooding.
As the sea rises, the outer boundary of these wetlands will erode, and new wetlands will form inland as previously dry areas are flooded by the higher water levels. The amount of newly
created wetlands, however, could be much smaller than the lost area of wetlands - especially in developed areas protected with bulkheads, dikes, and other structures that keep new
wetlands from forming inland. The IPCC suggests that by 2080, sea level rise could convert as much as 33 percent of the world’s coastal wetlands to open water.
IPCC, 2007
. Tidal wetlands are generally found between sea level and the highest tide over the monthly lunar
cycle. As a result, areas with small tide ranges are the most vulnerable. An EPA Report to Congress estimated that a two foot rise in sea level could eliminate 17-43 percent of U.S.
wetlands, with more than half the loss taking place in Louisiana
EPA, 1989
.
75
6 Disaster impacts and extreme natural hazard events
Urban environment is subjected to a variety of extreme events that could be a result of climate change although it is difficult to prove. In order to establish a correlation between the
disaster events and long term climate variability, it is useful to study past events and prioritize the types of extreme weather events in terms of resultant impact due to occurrence, degree of
intensities observed, frequency etc. This will give an indication of the prevailing vulnerabilities of the Urban areacity to long term climate change impact and subsequently
helpful in selecting appropriate adaptation options and course of actions to reduce such impacts. Flood has been identified as one of the most pressing issues in Thailand, with which
every year each and every pre-selected city has to cope up with. Subsequently inundation, water logging within urban areas, saline intrusion in coastal areas, landslides in hill slopes etc
trigger high and costly damages to the built environment. Moreover, erosion directly linked with water flow can lead to the total or partial destruction of buildings, infrastructure, utility
services etc. If the buildings do not get collapsed, the foundations will be weakened to such an extent that a failure may occur to such constructions in future even due to minor flood
events. The human losses and the resulting costs are thus substantial as seen in Table 6.1, and the time for a city to recover from the interruption to its infrastructure facilities, utility
systems, commercial and business establishments induce an even heavier burden and further economic losses. The other indirect consequences also are considerable which are not easy to
quantify and value in monetary terms such as inconvenience to urban population, destructions to social fabric, impacts to environment and natural resources etc.
The erosion process enhanced by sea level rise, on the coastal lines especially over the low- elevation coastal zones, induces the same risk. Thailand has 2,880 kilometers of coastline,
thus it is extremely vulnerable to sea level rises induced by climate change. A one meter rise will not only sink Bangkok and low-lying areas but also cause land subsidence and coastal
erosion; resulting in destruction of infrastructure, loss of beaches and irreversible damage to coastal ecosystems. The associated issue of saline intrusion within water bodies would be
also substantial. The map from the Center for International Earth Science Information Network at Columbia University Figure 6.1 highlights the 10 meters Low Elevation Coastal
Zone in Thailand with high rate of human settlements. The two pre selected coastal cities; Samut Sakhon and Phuket, both combine high population density with low elevation coastal
zone, leading thereby to high exposure to sea level rise. Adaptation measures can be planned to reduce the coastline exposure if the level of vulnerability can be estimated properly.
76
Figure 6.1. Map of LECZ of Thailand Source: CIESIN, Columbia University
77
6.1 Natural disaster events and impacts within the target provinces.
