Information Technology for Disaster Management (2001)
Herath S.
Geographical Information Systems in Disaster Reduction
Srikantha Herath
Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 158-8505, Japan
Abstract
Disaster reduction requires the integration of information from diverse sources. Geographic
Information Systems (GIS) is one new key technology often used to collect, store, analyse and
display large amount of spatially distributed information layers. The core of a GIS is a set of
spatially referenced maps, which are stored either as points, lines, polygons or raster data. GIS
makes it easy to assign attributes to these spatial quantities and combine different layers of
information.
Keywords: GIS technology; Disaster reduction
1. GIS
technology
Reduction
in
Disaster
Natural disasters are the outcome of
many
complex
geophysical
characteristics and the related social
circumstances that are subjected to a
hazard.
The
hazards
may
be
meteorological in origin such as cyclones,
severe storms, droughts and blizzards, or
may be earth processes such as
earthquake, volcanic eruptions, tsunamis,
etc., or a combination of both as in the
case of floods. All these events are
location dependent in the sense that a
hazard is aggravated by the geological,
topographical and land cover at the
location of the hazard. Similarly, natural
hazards turn into disasters when they
affect societies. The degree of damage is
dependent on the population density,
infrastructure and means available for
mitigation such as flood control dams and
evacuation facilities. In order to grasp the
impact of different disasters, it is
necessary to understand the interactions
and inter-relationships among these
diverse and complex entities subjected to
a given magnitude of the hazardous event.
The strength of GIS lies in the ability
to represent the real world situation
closely with layers of information (maps)
that can be combined in a predetermined
manner to identify the impacts of a
natural hazard through the introduction of
hazard dimension. In the case of floods,
the hazard information is represented as
water height, velocity and the flood
duration distribution over the catchment.
Combining this information with
population distribution helps identify
people at risk, with road network shows
available or passable roads for evacuation
and relief, with hospitals and emergency
facilities in planning response and relief
and with the property distribution in
estimating damage. In the case of
earthquakes, this information could be
ground shaking intensities due to an
earthquake, which again can be combined
with
population,
housing
and
infrastructure information to assess
disaster impact and plan response and
relief strategies.
GIS has developed substantially over
the past decade with the advent of large-
25
Information Technology for Disaster Management (2001)
Herath S.
volume data handling capabilities that
facilitates synthesising information from
many different data sources. It has
become an indispensable tool for
managing complex information related to
both
societal
and
environmental
functions.
Disaster reduction discipline has
benefited
largely
from
these
developments in risk map preparation,
damage assessment and modelling for
forecasting and planning.
The next section briefly describes the
current status and use of GIS in disaster
reduction.
considered to be equally distributed
regionally. This approach is adopted in
earthquake microzonation where each
location is subjected to the same type of
ground motion and vulnerability is
assessed based on the geological structure
of each location. In either approach, there
are many uncertainties in the assumptions
related to hazard scenario as well as in
the regional physical characteristics and
the forecasting models employed in the
hazard estimation. GIS is effective in
carrying out such analysis as automated
processes within the GIS, and different
outcomes resulting form changed input
parameters, assumptions and scenarios
can be easily compared with due
consideration given to uncertainties in
methodology and the input data.
In the case of flood risk map
preparation, first the flood extent estimate
is prepared, either from historical data or
through numerical simulation of selected
extreme events. If numerical simulation
is to be carried out, data other than the
meteorological input data is necessary to
supply a host of information related to the
locality depending on the type of
hydrological and flood plain model used.
At a minimum, it is necessary to have the
elevation information to determine the
surface gradients, and the land cover
information to estimate the surface
roughness of the catchment together with
the physical characteristics of the river.
The set up of a distributed hydrologic
model is schematically shown in Figure 1.
The topmost layer represents a
mathematical model in which the
catchment is divided into a large number
of grids. While the smaller grid sizes
allow higher accuracy, computational
capacity generally dictates the feasible
extent of a grid unit. The mathematical
model computes the water flow in the
2. Hazard Mapping
Identifying the risk from natural
disasters is an important requirement for
mitigation and preparedness. The
automation provided by GIS could be
directly used in microzonation, as the
basic
information
fusion
process
involving comparison, indices and
overlaying in microzonation is the same
for basic GIS operations. Depending on
the type of disaster, there are varying
approaches for preparing risk maps. For
example, in the case of floods, the
possible hazard scenarios are more
deterministic than for earthquakes or
cyclone disasters. In this case, hazard
maps
for
different
occurrence
probabilities are prepared first. This
could be, for example, flooding extent
due to rainfall intensities with different
return periods produced by scenarios
such as embankment overtopping,
embankment collapse, etc.
This
information is then combined with
population and infrastructure distribution
to prepare risk maps.
Another approach is the vulnerability
analysis, where the hazard potential is
26
Information Technology for Disaster Management (2001)
Herath S.
catchment resulting from rainfall using
equations that govern the water flow in
and out of each grid, and routes the flow
along slopes, to rivers and then along the
rivers. In order to use the water flow
equations, the properties of the location
such as slope, roughness, infiltration
capacity, etc., are required. These
properties are assumed to be uniform
within each grid and are estimated from
GIS layers of elevation, land cover and
soil property. Figure 2 shows the results
of such a simulation where flooding
occurs due to over-topping of the
embankments during a heavy rainfall.
Once the flood extent for a given
frequency has been established, the risk
can be estimated by overlaying the
population distribution and infrastructure
information on the inundation map. By
considering rainfall corresponding to
different return periods, flood extent
frequency maps are prepared and the risk
to people and assets subjected to flooding
can be established.
in case of floods or ground shaking
intensity in case of earthquakes. By
overlaying the map of hazard level onto
the property distribution map, the damage
estimation can be carried out either in an
external program or within the GIS
depending on the complexity of fragility
functions and the damage estimation
model.
Figure 3 schematically shows the
procedure to estimate the potential flood
damage
by the
above-mentioned
procedure. At first, a hydrological model
is used to estimate the inundation depth
and duration at each grid for the expected
scenario. If the damage due to a past
flood is to be estimated, then the
observed flood extent maps are converted
to a GIS layer so that floodwater height
and flood duration at each grid point is
known. Once this hazard information is
available, the damage in various
categories are estimated. For example,
one may distinguish between damage to
business and industry, damage to
residential housing, damage to crops and
farmhouses, etc. For each of these
categories, it is necessary to have what
are called fragility functions or damage
functions that relate the flood height and
duration information into economic loss.
These curves are prepared from the past
flood data for different residential
building categories as wooden, concrete,
industrial building types, etc. In order to
utilize all the information contained in
the fragility functions, information layers
that describe such property distribution in
each grid are required. As most of these
data are not readily available, GIS
analysis is used for creating them from
auxiliary data. As an example, if one
knows the number of food industry
complexes located in an administrative
3. Damage Assessment
Damage estimation for a potential
hazard is a key parameter in designing
mitigation measures. While it is difficult
to estimate intangible damage such as
injuries, or anxiety in a purely
deterministic manner, there are GIS
systems that are currently available or are
being developed to estimate both primary
and secondary tangible damage. The
methodology widely followed is to
establish fragility functions for different
types of property, such as residential and
non-residential buildings, infrastructure,
crops, farms, etc., which express the
potential damage as a percentage of cost
under a particular type of hazard, given
by the depth and duration of water height
27
Information Technology for Disaster Management (2001)
Herath S.
area, their distribution can be precisely
made in appropriate grids, if the locations
28
Information Technology for Disaster Management (2001)
Herath S.
29
Information Technology for Disaster Management (2001)
Herath S.
30
Information Technology for Disaster Management (2001)
Herath S.
are known. However, if locations are
not available, then land cover information
and road network data may be used to
distribute the industries within the
administrative units by considering only
highly urbanized land cover areas located
within a certain distance to the roads.
Once the hazard dimension, i.e. flood
height and the property distribution, is
prepared, then the total damage in each
grid is estimated using a fragility function
for each property type identified within
each grid subjected to the water level in
that grid. Integrating this information
over the inundated area provides the total
loss resulting from the event. Figure 4
shows the economic loss distribution
estimated following such a procedure.
reconstruction are reported. In more
specific examples of usage, GIS is a tool
in securing lifelines such as gas, water
and electricity. Up-to-date GIS systems
specifying the state of lifelines is a must
for identifying and isolating network
components that have been rendered
inoperable during disasters. GIS has been
heavily used in the recovery process in
the aftermath of a disaster. GIS had been
used to identify locations for evacuation
and resettling soon after the disaster.
Demolition and reconstruction have been
greatly assisted by GIS technology in the
aftermath of the Northridge and Kobe
earthquakes. GIS has also been used in
selecting locations for resettlement after a
disaster.
4. Support
Modelling
4.2. GIS in Response
for
Simulation
and
For disaster response, it is necessary to
identify passable roads, locations of
emergency services, refugee camps,
feasible transportation routes and a host
of other information which can only be
derived by combining the most recent
disaster area status information with other
static information related to the
infrastructure.
In the past, GIS-based response
systems have been successful in the
firefighting industry, where the spread of
fires and fire conditions can be
generalised and the systems are used
continuously. During major disasters, the
chaos and the rapidly changing situations
have prevented the use of GIS in
response, although many response
systems have been developed or are
under development. The recent rapid
advancement and easy access to GPS and
mobile communication are now leading
the development of real-time innovative
response systems. As a typical example
Mathematical
simulation
and
modelling disaster processes is the main
procedure in forecasting or warning, as
well
as
in
impact
assessment.
Unfortunately, present day GIS cannot
handle time-varying information or
dynamic updates of information required
in the modelling of disasters. However,
GIS is widely used to prepare the input
information to mathematical models as a
pre-processor. The ability of GIS to
process complex spatial information as
input data has in turn helped to produce
more complex models capable of
representing the disaster scenarios in
more detail.
4.1. GIS in Planning
GIS has become a prominent tool for
city and infrastructure planning in general.
In the disaster mitigation field, several
uses in land management, response and
31
Information Technology for Disaster Management (2001)
Herath S.
32
Information Technology for Disaster Management (2001)
Herath S.
to illustrate the methodologies,
consider an accident where a chemical is
released into the air from an industrial
complex. With the information on the
quantity and time of the chemical release,
the diffusion process can be modelled
using the most recent information on
wind velocities in the area coupled with
the information on buildings and other
infrastructure in the vicinity. Once the
spread and timing is known from the
modelling study, disaster managers are
alerted to the situation with information
on expected risk and occurrence time.
Their response can be made more
effective by supplying information on
people at risk in the target area such as
homes for elderly, schools, etc. In order
to make such systems operational, it is
necessary to have easily accessible
infrastructure and demographic databases
in GIS available to a range of responsible
organizations. Ideally, the development
of such systems should aim at integrating
diverse information from more than one
source, with a forecasting system to
arrive at possible consequences. Then
this information has to be disseminated to
persons responsible for responding to the
situation. Hence, the coupling of GIS
with communication and modelling tools
are a necessity in using GIS for disaster
response.
though hardware prices have been
steadily declining. On the other hand,
software as well as training requires a
significant amount of resources. Before
the benefits of GIS become available, a
considerable investment in time and
resources is required in system
development, data preparation and
training.
At the global level
It is important to realize that GIS is only
a tool for overlaying maps, though it
makes such overlay and integration easy.
The results of GIS processing are
determined by the analyses carried out
and the quality of data. The most
expensive part of the GIS use lies in the
data preparation. It is important to note
that more and more regional and global
data of topography, land cover, soil
characteristics, etc., prepared under
various international and regional
collaborative programs are becoming
freely available. This makes it possible to
start on GIS programs with base data sets
that can be upgraded with more detailed
data if the need arises.
At the national level
In preparing data for GIS, it is extremely
important that data--especially the static
data that does not change often--are
produced as collaborative efforts between
various
governmental
and
other
interested organisations. Experience
shows that unnecessary duplication of
this expensive endeavour is delaying the
widespread use of GIS in many countries.
It is important for governments to have a
national policy on the development and
sharing of digital data related to disaster
mitigation efforts.
4.3. Overview of GIS Utilisation
GIS technology is helpful in
integrating data from various sources in
all phases of a disaster cycle. GIS
information, especially, can be easily
combined with detailed land cover
information obtainable from remote
sensing, thereby updating the dynamic
component
of
information.
GIS
technology is not inexpensive, even
33