Journal of Natural Disaster Science, Volume 26, Number 1, 2004, pp1-14

Assessment of flood risk in Hat Yai Municipality, Southern Thailand, using GISCharlchai TANAVUD1, Chao YONGCHALERMCHAI2,
Abdollah BENNUI3 and Omthip DENSREESEREKUL2
Disaster Studies Center, Prince of Songkla University
Faculty of Natural Resources, Prince of Songkla University
3
Research and Development Office, Prince of Songkla University
1

2(Received for 5. Apr., 2004 and in revised from 1 Sep., 2004)

ABSTRACTThis article assesses the risk of flooding and identifies efficient measures to reduce flood risk in Hat Yai
Municipality, southern Thailand using GIS and satellite imagery. The center of commercial trade and administration in southern Thailand, Hat Yai is located in the downstream area of the Khlong U-Taphao Basin. From 1982
to 2002, forest resources in the basin’s upstream were decreased from 48,281 to 26,781 hectares, equivalent to a
reduction of 44.5 %. This was largely attributable to the expansion of rubber cultivation. Further analysis
revealed that 17,116 ha, 42.7 % of the forest resources in the basin’s headwater source areas mainly had been
replaced by rubber plantations. As a consequence of extensive deforestation, particularly in headwater sourceareas, the municipality has become vulnerable to natural disasters; primarily floods.
Hat Yai Municipality experienced two flood events of catastrophic magnitudes in 1988 and 2000. These
destructive floods were detrimental to its vulnerable social and economic development due to the loss of life anddestruction of property. Since the 2000 flood, considerable structural mitigation measures have been undertaken
to prevent and alleviate future flooding of the municipality. Recent flooding on 10 December 2003, caused by astorm like that experienced in 2000, indicates that structural mitigation efforts undertaken so far are inadequate towithstand natural threats. Hat Yai Municipality will continue to be extremely vulnerable to future flood disasters.
This shows the compelling need to increase the municipality’s resilience against flooding through adoption in the
coming year of non-structural disaster reduction schemes to supplement existing efforts. Risk assessment based on
hazard and vulnerability analysis is needed to identify and implement adequate and successful non-structural alternatives.
Analyses showed that 99.0, 400.0, 1110.0, 346.0, and 100.0 ha of the municipality’s total land areas were subjected respectively to very low, low, moderate, high, and very high flood hazards. Further analysis revealed that
39.6, 654.6, 152.7, 664.5, and 543.6 ha of the land areas respectively faced very low, low, moderate, high, andvery high flood risks. Analyses also showed that all the residential, commercial, industrial, and the public utilities
and facilities areas, equivalent to 1,188.0 ha (57.8 %) of the municipality’s total land area, faced high and very
high flood risks. Measures to reduce the risk of flooding in Hat Yai Municipality are discussed.

1. INTRODUCTION
Hat Yai Municipality, comprising 33 communities, covers an
area of 20.1 km2 and has a population of 157,876 people. The
municipality, located in the downstream area of the Khong UTaphao Basin, is the center of commercial trade and administration
in southern Thailand. Its ideal geographical location also makes it
a gateway to the major neighbouring countries of Malaysia andSingapore, and is thus a city with high tourism potential fordomestic and foreign tourists who visit year-round. Due to its geographical characteristics and to unplanned urbanization and deforestation in upstream areas, Hat Yai Municipality has become
extremely vulnerable to flood disasters. With its population density and as a commercial center, the municipality has characteristics
that can magnify the impact of flooding to which it is prone. The
unprecedented flooding of 21 to 24 November 2000, triggered bytorrential rains, has been described as one of the worst natural disasters in the history of urban Thailand. It claimed 30 lives andseverely damaged public utilities, critical facilities, and commercial and industrial establishments. Estimated total economic losses
exceeded US $ 220 million. Indirect losses in terms of lost production and the cost of economic recovery make the estimationeven higher. The losses caused by this adverse natural phenomenon have deprived the municipality of resources which could be
used for social and economic development, thus impeding development. Future recurrences of flooding on the scale of the year
2000 disaster are anticipated because the municipality continues toengage in activities that increase the hazard potential, as well as
economic and personal vulnerability to flood damage.
In recognizing the high likelihood of future flood disasters andthe increased severity of flooding, Hat Yai Municipality has madeconsiderable investment in flood mitigation schemes. Extensive
works, including the construction of levees, drainage canals, water
diversion channels and pumping stations, have been undertaken toprevent and alleviate flooding since the November 2000 catastrophe. In spite of these considerable structural mitigation activities,

KEY WORDS: flood disaster, risk assessment, risk reduction measures, Geographic Information Systems, satellite imagery

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C. TANAVUD, C. YONGCHALERMCHAI, A. BENNUI AND O. DENSREESEREKUL

large areas of the municipality were submerged during the 10
December 2003 flood caused by rain storms of November 2000
magnitudes. The 2003 flooding indicated that the structural efforts
undertaken so far are not adequate. Hat Yai Municipality therefore
remains and will continue to be extremely vulnerable to future
flooding.
It is important to recognize that there is a close relationshipbetween water source areas in the upland watershed, transportareas in the foothill and terrace, and discharge areas in the lowlands of the Khlong U-Taphao Basin. These areas are inter-connected throughout the basin by the U-Taphao River and its tributaries, hence disturbances in upstream areas can prove detrimental
downstream where Hat Yai Municipality is located (Tanavud et al.,2001a). For instance, deforestation of the mountainous upper
watershed can increase the physical magnitude of the flood hazard
and contribute to downstream flood damage (WHO, 2002). The
hazard of flooding is known to be governed by the condition of
upland ecosystems as well as those in the lowlands which increase
the hazard or vulnerability. Measures that address flooding thatposes a risk to the municipality downstream therefore need to be
adopted in the context of the watershed basis. To identify andimplement the most effective responses to flood hazards, risk
assessment based on a hazard and vulnerability analysis needs tobe made. Our study therefore aimed to assess the flood risk in Hat
Yai Municipality in order that adequate, successful risk reduction
schemes can be identified and measures taken to prevent futuredisasters.
2. MATERIALSThe data and their sources used to create a land-use map of
the Klong U-Taphao Basin, and to assess flood risk in Hat Yai
Municipality are reported below and in Table 1.
2.1 Klong U-Taphao Basin
1) Topographic maps for the areas studied on a 1 : 250,000
scale, produced by the Royal Thai Survey Department.
2) Land satellite images for the areas studied on a 1 : 250,000 as
well as a 1 : 50,000 scale, produced by the Geo-Informatics
Table 1.

and Space Technology Development Agency (GISDA).
3) Watershed classification map for the areas studied on a
1 : 50,000 scale, produced by the Office of Environmental
Policy and Planning (OEPP).
4) Government department records on soil, land use, and watershed classes.
2.2 Hat Yai Municipality
1) Aerial photo of Hat Yai Municipality on a 1 : 4,000 scale,produced by the Royal Thai Survey Department.
2) Elevation map of Hat Yai Municipality on a 1 : 4,000 scale,produced by the Department of Public Works and Town andCountry Planning.
3) Slope map of Hat Yai municipality on a 1 : 4,000 scale, produced by the Department of Public Works and Town andCountry Planning.
4) Drainage map of Hat Yai Municipality on a 1 : 4,000 scale,produced by Hat Yai Municipality.
5) Government department records of population, rainfall, landuse, and drainage systems.
2.3 Land-use changes in the Klong U-Taphao Basin.
In this study, Geographic Information Systems (GIS) wereused to develop two digitized thematic maps that included basinboundaries, as well as 1982 and 2000 land-use maps. All GIS
computations and coverage overlays were performed with PC
ArcInfo software. Basin boundaries were digitized from the1 : 50,000 topographic maps. Land-use coverage for 1982 and2000 were generated in ArcInfo format by digitizing from land-use
maps visually interpreted from the 1982 and 2000 Landsat TM
images of the areas studied.
According to the Watershed Classification System, developedby the Office of Environmental Policy and Planning (OEPP), areas
in watershed classes 1 and 2 are designated as headwater sourceareas. The data layer of these headwater areas was generated bydigitizing from the 1 : 50,000 watershed classification maps. The
resulting coverage, created by overlaying the 2000 land-use map
and the headwater source areas map, using PC ArcInfo, generated
a land use in headwater areas map.

Data and their sources.

ASSESSMENT OF FLOOD RISK IN HAT YAI MUNICIPALITY, SOUTHERN THAILAND, USING GIS

2.4

Flood catastrophes in Hat Yai Municipality in 1988 and 2000.
Data on flood water levels during the 1988 and 2000 floodcatastrophes were obtained by a questionnaire survey. The survey
was undertaken across the municipality, and twenty interviews
were made per one square kilometer. A contour map showing
variations in flood water levels at all locations across the municipality was generated from water level data obtained by use of thesurface analysis function of ArcView 3.2 software.
3. METHODS
The flood hazard and flood risk assessment was done as follows:
3.1 Database inputs.
1) Flood hazard assessment.
A disaster is comprised of three components; hazard, risk, andvulnerability. The hazard is the probability of the occurrence of apotentially damaging phenomenon within a given period of timeand space. Data layers that were selected as input data for assessing flood hazard in Hat Yai Municipality using ArcInfo GIS
included rainfall, elevation, slope, drainage density, road density
and land-use type. Selection of these factors was based on quotation frequencies in flood-related publications as well as theauthors’ knowledge of past floods in the area being investigated(Tanavud et al., 2001b). Basin boundaries were digitized from thetopographic maps using GIS ArcInfo. Because the magnitude of astorm event represented by rainfall duration-intensity is a contributing factor to the occurrence of landslides and flooding insouthern Thailand (DeGraff, 1989; Rau, 1991), a seven-day periodof rainfall prior to the 21-24 November 2000 flood was used to
produce a rainfall isohyet map. Elevation and slope maps in thescale of 1 : 4,000 in digital format were provided by the
Department of Public Works and Town and Country Planning.
The drainage map was created in Arc/Info by digitizing from apaper map produced by Hat Yai Municipality. A land-use mapthat included roads and railways was created by digitizing from a
map interpreted visually from the 1 : 4,000 aerial colour photo mapof 2002. The resulting coverage created by the overlay of thesemaps generated the flood hazard map.
2) Flood risk assessment.
Risk refers to the threat to life or property that may result
from the action of a hazard upon some structure, system, or population (French, 1991). There are three components in assessing
risk of disasters (Tobin and Montz, 1997). The first is the hazard;
the probability of the occurrence of potentially damaging phenomena within a specified time and given area. The second is the element or elements at risk. These mainly are regarded to be population, property, and economic activities in a given area. The third isvulnerability; the degree of loss for a given element or set of elements at risk. According to Shook (1997), risk can be presented as
Risk = (Elements at risk) (Hazard × Vulnerability)
Due to the scarcity of reliable information, the elements at riskin this study primarily were assessed based on population and land
use in the municipality. Regarding vulnerability, the recent 10
December 2003 flooding in the municipality indicated that thestructural mitigation measures undertaken so far are not adequate,
therefore the vulnerabilities to flood loss of the people, property,
and public utility and critical facilities is absolute, representing

3

total loss.
A population density map was created in ArcInfo GIS byimporting population data from the Department of Provincial
Administration. A land-use map of Hat Yai Municipality was produced by digitizing from the land-use map interpreted visuallyfrom the 1 : 4,000 aerial colour photo map of 2002 produced by
the Royal Thai Survey Department. A flood risk map then was
created by overlaying the flood hazard map with the population
density and then the land use maps.
3.2 Flood hazard and risk mapping.
1) Flood hazard map.
The flood hazard map in our study was created by the weighting and ranking technique of Pachauri and Pant (1992). This technique is a numerical system based on biophysical factors which are
directly or indirectly correlated with the occurrence of floods. The
factors were weighted according to their relative importance toeach other and to their expected importance in causing floods.
Further, each factor was partitioned into five subfactors, each ofwhich was ascribed a ranking value. The higher ranking value themore susceptible the particular subfactor to the occurrence offloods.
Rainfall, elevation, slope, drainage density, road density andland use were chosen as the most influential factors for evaluating
the flood hazard to the municipality. Selection of factors and subfactors for the generation of the flood hazard map was based on
quotation frequencies in flood-related publications and on theauthors’ knowledge of past flooding in southern Thailand(Tanavud et al., 2001b). Of the factors selected, the highest
weighting was given to rainfall, followed by elevation, slope,drainage density, road density, and land use. After the weighting
procedures, each factor was partitioned into five subfactors, eachof which was given a ranking value (Table 2). For each factor, theweighted hazard ranking was obtained by multiplying its weight by
the ranking value for the corresponding subfactor. Pramojanee etal. (1997) and Tanavud et al. (2000) provide greater details on theweighting and ranking techniques. The total estimated hazard,
obtained by adding the weighted flood rankings of all the factors,
was classified in five categories; very low, low, moderate, high,and very high (Table 3).
2) Flood risk map.
A flood risk map was created by use of the same weighting
and ranking technique used for mapping flood hazard areas.
Hazard, population, and land-use types were selected as the mostinfluential factors in evaluating flood risk. For land-use types,
because residential, commercial, and industrial areas generally are
more valuable than institutional areas (government agencies’
offices, hospitals, banks, schools and universities), public utilities
and critical facilities areas (power, water, roads and railways) andagricultural land, higher weighting values were given to residential, commercial, and industrial areas, followed in descending orderby institutional areas, public utility and critical facility areas, andagricultural land (Table 4). The total estimated risk, obtained byadding the weighted risk rankings of all factors, also was classified
in five categories; very low, low, moderate, high, and very highrisk (Table 5). Tanavud et al. (2001b) provides additional details
on the flood hazard and risk mapping methods.

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C. TANAVUD, C. YONGCHALERMCHAI, A. BENNUI AND O. DENSREESEREKUL

Table 2.

Table 3.

Weighted flood hazard rankings for Hat Yai Municipality.

Maximum and minimum values of the total estimated hazard
for each flood hazard category.

Table 4.

Weighted flood risk rankings for Hat Yai Municipality.

ASSESSMENT OF FLOOD RISK IN HAT YAI MUNICIPALITY, SOUTHERN THAILAND, USING GIS

Table 5.

Maximum and minimum values of the total estimated riskfor each flood risk category.

Table 6.

Land use changes in the Klong U-Taphao Basin, 1982 to 2002.

Table 7.

Land use in headwater source areas of the Klong U-Taphao Basin.

Table 8.

Changes in land use in the Klong U-Taphao Basin, 1982 to 2002.

Land use in 1982
Rice

ForestUrban / built-up
areas

Miscellaneous

4. RESULTS AND DISCUSSION
4.1 Land use changes
In 1982, in the Klong U-Taphao Basin, forests covered an
estimated 48,281 ha, equivalent to 20.5 % of the basin’s total landarea (Table 6). Over a period of 20 years, from 1982 to 2002,
these forests were depleted by a total of 21,500 ha, equivalent to anannual loss of 1,075 ha (Figures 1 and 2). As a result, by 2002,
forests accounted for only 11.4 % of the basin (Table 6). Duringthat same period, the proportion of rubber plantation areas expanded dramatically from 150,218 to 172,130 ha, an annual increase of
1,096 ha (Table 6). In southern Thailand, such encroachment andconversion of natural forests to other uses has been attributed tothe expansion of agricultural land, illegal logging, and lack of pub-Land use in 2002
Aquaculture
Rubber

Water bodies

Orchards

Perennialcrops

5

MangrovesTotal (ha)lic awareness of the flood protection values of forests (UNDP,
1994).
The municipality’s land-use map, when overlaid with the
headwater source areas map, provided new insight into the statusof land use in headwater areas. These types of environmentally
critical areas had been designated by the Watershed Classification
System as “protected forest”, but of the 42,084 ha of headwater
areas, 17,116 ha, 42.7 percent, had already been converted to otheruses (Table 7). Indeed by 2002 or 42.5 % of the headwater areas
had been converted to rubber plantation.
Overlaying the land-use map of 1982 with that of 2002
revealed that a 21,912 ha increase in rubber cultivation areas camefrom the conversion of 22,631 ha of forest area, 4,855 ha of rice
fields and 2,513 ha of mixed orchards (Table 8). The dramatic

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C. TANAVUD, C. YONGCHALERMCHAI, A. BENNUI AND O. DENSREESEREKUL

Fig. 1

Land use map of Khlong U-Taphao Basin in 1982.

ASSESSMENT OF FLOOD RISK IN HAT YAI MUNICIPALITY, SOUTHERN THAILAND, USING GIS

Fig. 2Land use map of Khlong U-Taphao Basin in 2002.

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C. TANAVUD, C. YONGCHALERMCHAI, A. BENNUI AND O. DENSREESEREKUL

increase in the price of rubber during this period and the subsidies
provided by the Thai Government’s Office of Rubber Replanting
Aid Fund have been instrumental in promoting land conversion torubber plantation (Usher, 1994). Complete land-use change,
including land converted to other uses and land formerly in otheruses, is shown in detail in Table 8.
4.2 Consequences of land-use changes.
Ecological transition in the basin’s uplands, particularly inheadwater source areas, from natural forest to rubber plantations
disturbed the finely tuned equilibrium of the natural ecosystems tosuch a degree that environmental stability was compromised(Donovan, 1989). This change limited the basin’s ability to absorb
the impact of a flood and lowered the resilience of the natural
ecosystem to hazard impact (United Nations, 2002).
Consequently, Hat Yai Municipality has become extremely vulnerable to natural disasters, primarily floods (ESCAP, 1989). Suchcalamitous events inhibit vulnerable social and economic development through the loss of life and destruction of property, as in Hat
Yai Municipality in November 1988 (Rau, 1991) and in November
2000 (Bangkok Post, 2000).
4.3 Flood events in Hat Yai municipality in 1988 and 2000.
Hat Yai Municipality experienced floods of catastrophic magnitude in 1988 and 2000. The flood water levels of those floods
are shown in Table 9. In 1988, it was estimated that 114 ha (5.6%) of the municipality’s total land area were inundated at depths of
2 to more than 3 meters (Figure 3). As shown in Figure 4, in 2000,
the area facing the same flood water depth had increased to 452 ha(22.0 %) of the municipality, an increase of 348 ha (334.6 %)(Table 9). It should be noted that areas inundated to depths greaterthan 3 meters increased from 6 ha (0.3 %) of the municipality’s
total land area in 1988 to 16 ha (0.8 %) in 2000. This indicates
Table 9.

that the severity of flooding in Hat Yai had increased greatly overthe 12 year period from 1988 to 2000. Recurrence of flooding on
the scale of or greater than the November 2000 disaster are anticipated because residents are continuing activities that increase flood
hazard as well as economic and personal vulnerability to flood
damage. Therefore, there is the urgent need to make the community resilient to flood hazard through the adoption of disaster reduction schemes. To identify adequate disaster reduction activities, aflood risk assessment based on hazard and vulnerability analysis isneeded.
A mapped inventory of areas inundated or devastated during
the 2000 catastrophic-level flooding should be published and distributed to the community at large. Such a map would remind theresidents of the disastrous consequences of such flooding. The
municipality must learn to live and cope with floods in order toreduce its vulnerability to flood damage and learn how to increase
emergency preparedness to deal with loss of life and property.
4.4 Flood risk assessment.
1) Hazard analysis.
From the flood hazard map, it was estimated that 99.0, 400.0,
1110.0, 346.0 and 100.0 ha of the municipality’s total land areas
were subjected respectively to very low, low, moderate, high, andvery high flood hazards (Table 10). Further analysis revealed that137.4 ha (24.5 %) and 85.6 ha (21.4 %) of residential and public
utility and facility areas respectively, face high and very high flood
hazard levels (Figure 5 and Table 10). The flood risk map showsthat 39.6, 654.6, 152.7, 664.5 and 543.6 ha of the municipality’sland areas faced respectively very low, low, moderate, high, andvery high flood risks (Figure 6 and Table 11). Moreover, all theresidential, commercial, industrial and public utility and facility
areas, equivalent to 1,188.0 ha (57.8 %) of the municipality’s total
land area, face high and very high levels of flood risk (Table 11).

Flood water levels in Hat Yai Municipality during the 1988 and 2000 floods.

Table 10.

Vulnerable features in Hat Yai Municipality for various hazard levels.

ASSESSMENT OF FLOOD RISK IN HAT YAI MUNICIPALITY, SOUTHERN THAILAND, USING GIS

Fig. 3

Map of water level in 1988 flood event in Hat Yai Municipality.

Fig. 4

Map of water level in 2000 flood event in Hat Yai Municipality.

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C. TANAVUD, C. YONGCHALERMCHAI, A. BENNUI AND O. DENSREESEREKUL

Fig. 5Flood hazard map of Hat Yai Municipality.

Fig. 6

Flood risk map of Hat Yai Municipality.

ASSESSMENT OF FLOOD RISK IN HAT YAI MUNICIPALITY, SOUTHERN THAILAND, USING GIS

Table 11.

Table 12.

11

Vulnerable features in Hat Yai Municipality for various risk levels.

Distribution of areas susceptible to flood hazard in Hat Yai Municipality.

Consideration therefore should be given to adopting adequate measures to decrease the flood hazard in these areas.
2) Vulnerability analysis.
Utilizing the overlay facility provided in the GIS ArcInfo, thehazard map was overlaid with the municipality’s land-use map.
The findings explicitly show that 137.4 ha (24.5 %) of residential

areas face high or very high flood hazards, and that 85.6 ha (21.4%) of these areas used for public utilities and facilities are subject
to high and very high flood hazards (Table 10). Furthermore, 82.3
ha (63.2 %) of Banghuk Community’s total land area and 84.8 ha(66.9 %) of the Rimkuen Community area respectively face highand very high flood hazards (Table 12). Further analysis showed

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C. TANAVUD, C. YONGCHALERMCHAI, A. BENNUI AND O. DENSREESEREKUL

Table 13.

Distribution of areas susceptible to flood risk in Hat Yai Municipality.

that 64.1 ha (50.5%) of Rimkuen Community’s land area was subject to high and very high flood risk (Table 13).
It is important that Hat Yai Municipality publishes hazard andrisk maps in hard copy and distribute them to the communities inorder to enhance public awareness about the levels of flood hazard
and flood risk they are likely to face. As of today, no municipality
in Thailand has maps of this level of accuracy and degree of detail.
4.5 Risk reduction measures.
Complete prevention of floods through structural measures isalmost a physical impossibility and is uneconomic (Askew, 1991).
Properly designed and operated flood works, however, can preventor mitigate flood damage within physical and economical limits.
The application of structural mitigation activities, however, may
have a negative impact on life, property and the natural environment (Ertuna, 1991). For instance, construction of levees throughout low-lying areas without providing adequate drainage facilities
can lead to internal flooding that adversely affects residents.
Levees may also worsen the hazard in other locations by divertingwater from one area into another, and may deprive the naturalenvironment of critical habitats, such as wetlands. Furthermore,construction of large infrastructure type projects, such as drainage
canals or diversion channels, to prevent and mitigate flood disasters is realized as no longer feasible in Hat Yai Municipality due tothe scarcity of available land and the impact on the natural environment. Structural mitigation practices therefore should not beviewed as a panacea for all the problems associated with floodingin this municipality. To effectively reduce the risk of flooding, analternative approach that focuses on non-structural measures isneeded to supplement existing structural efforts. Such non-structural
alternatives would not involve major construction and therefore could
have proportionately less environmental impact (Geipel, 1993).
Risk of flooding can be reduced by decreasing hazards, reducing or eliminating the vulnerability of the elements at risk, or a
combination of both actions (DeGraff, 1989). Adoption of nonstructural risk reduction measures, including development of landuse planning, installation of flood forecasting and warning systems, adoption of preparedness measures against flooding, and cre-

ASSESSMENT OF FLOOD RISK IN HAT YAI MUNICIPALITY, SOUTHERN THAILAND, USING GIS

ation of risk-transfer instruments, such as insurance, in flood risk
areas can effectively reduce the effect of flooding on lives andproperty. Application of land-use planning can reduce flood hazards by allocating less vulnerable land uses to the most hazardous
areas or by avoiding development in those locations. Relocation of
the residents of high risk areas would reduce their vulnerability.
Creation of a “culture of safety” in flood-prone areas also could
reduce a flood-effected community’s vulnerability by creating people’s awareness of possible flooding or by the building of safer
housing that will withstand flooding in areas vulnerable to future
flood damage. The design and installation of flood-forecasting and-warning systems which allow people in high risk areas to move toless hazardous locations during flooding can effectively reduce theelements at risk. Local preparedness to cope with potential disasters also would effectively reduce loss of life and damage to property in high risk areas. Introduction of insurance to spread thelosses of future floods among those directly affected also could be
used to reduce risk of future floods.
Several environmental management measures could also be
implemented to reduce the flood disaster risk (United Nations,
2002). For instance, maintenance of the environmental and ecological stability of the upland watershed through the enrichment offorest cover to restore its flood protection values, prevention of
encroachment by cultivators to maintain a resilient environment toavert future disaster, and adoption of soil and water conservation
measures in upland cultivation to reverse environmental degradation, can be used to reduce flood hazards. To enhance the naturalresilience to future floods, the basin’s headwater source areas
should be demarcated for further enhancement of the forest environment. Wetland functions, particularly water storage, should be
rehabilitated and conserved to absorb the impact of flooding.
Prevention of drainage congestion by removing soil sediment,
debris, and weeds that block stream channels also is an environmental action that reduces vulnerability. In addition, flood risk
assessment should be incorporated in the requirements of theEnvironmental Impact Assessment (EIA). An expanded EIA
process would provide the basis to ensure that all proposed initiatives would include considerations both of vulnerability reduction
and lessening the environmental impact. It is anticipated that the
adoption of non-structural risk reduction measures and the incorporation of environmental dimensions into risk reduction schemes
would enable Hat Yai Municipality to become more resilient to theeffects of flood hazards and support sustainable development bothin the municipality and southern Thailand.

13

withstand flood threats. Recognizing the frequency and increased
severity of flooding in this municipality, non-structural alternatives
to reduce flood risks need to be promoted to supplement existing
structural investments. Therefore, it is recommended that Hat Yai
Municipality adopt the following non-structural actions as a matterof priority to strengthen and improve its ability to better respond toflood risks:
1) Set up a Hat Yai Disaster Management Authority (HYDMA).
The authority, chaired by the Songkla Governor, should comprise a body made up of representatives from concerned government agencies, experts, academics, NGOs and local residents. The authority would propose, for approval, policies andmeasures for flood disasters. An annual meeting of the authority would be held before the rainy season to study and review
the progress of measures based on up-to-date information, tocheck operational readiness for potential flood disasters, and toprepare proper measures and action plans. The authority would
also be responsible for managing and coordinating responses
and relief measures during flooding.
2) Raise the awareness of the municipality’s residents. They need
to be aware of the natural hazards likely to be faced, what specific preparations need to be made before an event, what to do
during the event, and what actions to take in its aftermath.
Brochures, posters, calendars, and public service announcements on radio and television should be used to stimulate public awareness.
3) Improve the forecasting and warning systems. Notice of animpending flood disaster issued well in advance can protect
lives and property. Prediction accuracy and lead times therefore should be improved through the application of such stateof-the-art science and technology as radar and weather satellite
information. Concerted effort is also needed to improve socialand organizational abilities to disseminate warnings.
4) Undertake research on disaster-related topics. Even though theprediction capability for flood hazards in the Khlong U–Taphao
Basin, in which Hat Yai Municipality is located, have increased
significantly, further research and modernization of weather
prediction facilities are required to provide the accuracy andlead time critical to decision makers who need to activate evacuation plans. Application of advance techniques in soil
physics, geotechnical engineering, GIS and remote sensing forflood risk assessment and reduction also are needed. Researchshould be accelerated to determine what the detrimental
impacts of flood disasters are on human health and the naturalenvironment.

5. CONCLUSIONS AND RECOMMENDATIONS
Due to geographical characteristics, unplanned urbanizationand deforestation in the upland watershed, Hat Yai Municipality
has a high level of flood risk. Flooding has become a regular phenomenon and continues to threaten the vulnerable social and economic infrastructure of the municipality. Extreme flood events
have had devastating effects on the standard of living of the population and on development prospects. In attempts to prevent andmitigate catastrophic flooding, considerable mitigation works havebeen undertaken in Hat Yai Municipality, most of them structural.
The flooding of 10 December 2003, however, demonstrated thatthese structural measures undertaken so far are not adequate to

ACKNOWLEDGEMENTS
This work was funded by USAID as part of the Thailand
Urban Disaster Mitigation Project, implemented by the ADPC.
We express our sincere thanks to Hat Yai Municipality, theDepartment of Public Works and Town and Country Planning, theDepartment of Land Development, and Songkla Province for theirsupport and cooperation. The constructive criticism and insightfulcomments made on an earlier draft of this manuscript by two
anonymous referees are greatly appreciated. We hope that thisstudy will help to further the progress of disaster management insouthern Thailand.

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C. TANAVUD, C. YONGCHALERMCHAI, A. BENNUI AND O. DENSREESEREKULREFERENCES
Askew, A. 1991. Learning to live with floods. Nature and Resources 27 (1): 4-8.
Bangkok Post. 2000. Southern flooding: Aid pours in as death toll rises.
Bangkok Post Newspaper. 25 November 2000. Bangkok.
DeGraff, J.V. 1989. Landslide activity resulting from the November 1988
storm events in southern Thailand and associated resource recovery
needs. p. 1-43. In Safeguarding the Future. Restoration andDevelopment in the South of Thailand. Jiramedha Advertising and
Printing, Bangkok.
Donovan, D. G. 1989. Rehabilitation and development of forest and uplandresources in the storm-damaged areas of southern Thailand. p. 197244. In Safeguarding the Future. Restoration and Development in theSouth of Thailand. Jiramedha Advertising and Printing, Bangkok.
Ertuna, C. 1991. Integrated approach to flood disaster management andrural development. p. 93-110. In Disaster Management and Regional
Development Planning with People’s Participation. Vol. 2. United
Nations Centre for Regional Development. Dhaka, Bangladesh.
ESCAP. 1989. ESCAP Technical Assistance to Flood-effected Areas inSouthern Thailand. Mission to Surat Thanni and Nakhon Si
Thammarat Province. 12-16 December 1988. ESCAP Mission Report.
Bangkok.
French, S. P. 1991. Utilization of Geographic Information Systems forLand Use Planning and Disaster Preparedness. p. 3-28. In Disaster
Management and Regional Development Planning with People’s
Participation. Vol. II. United Nations Centre for Regional
Development. Dhaka, Bangladesh.
Geipel, R. 1993. The river Danube flood of 27 March 1986. p. 111-118. In
Nemec, J., Nigg, J. and Siccardi, F (eds). Prediction and Perception of
Natural Hazards. Symposium Proceedings. Dordrecht, The
Netherlands.
Pachauri, A.K. and M. Pant. 1992. Landslide hazard mapping based on
geological attributes. Engineering Geology 32 : 81-100.
Pramojanee, P., C. Tanavud, C. Yongchalermchai and C. Navanugraha.

1997. An application of GIS for mapping of flood hazard and risk
area in Nakorn Sri Thammarat Province, South of Thailand. p. 198207. In Proceedings of International Conference on Geo-Informationfor Sustainable Management. 17-21 August 1997. ITC. Enschede, The
Netherlands.
Rau, J. L. 1991. Assessment and mitigation of landslides in rural areas insoutheast Asia. p. 210-235. In Disaster Management and Regional
Development Planning with People’s Participation. Vol. 2. United
Nations Centre for Regional Development. Dhaka, Bangladesh.
Shook, G. 1997. An assessment of disaster risk and its management inThailand. Disasters 21 (1) : 77-88
Tanavud, C., C. Yongchalermchai, A. Bennui and C. Navanugraha. 2000.
Application of GIS and Remote Sensing for Landslide Disaster
Management in Southern Thailand. Journal of Natural Disaster
Science. 22 (2) : 67-74
Tanavud, C., P. Kheowvongsri, C. Yongchalermchai, W. Leowarin, O.
Densrisereekul, A. Bennui, J. Murase and M. Kimura. 2001a. Effectsof land use patterns on soil and water quality in Khlong U-Taphao
Basin. Thai. J. Agric. Sci. 34 (1-2) : 15-31.
Tanavud, C., C. Yongchalermchai, P. Pramojanee, W. Wangworawut, A.
Bennui, O. Sukboon and P. Pramojanee. 2001b. Application of GIS
and Remote sensing techniques for flood disaster management in
Songkla Province. Songklanakarin. J. Sci. Technol. 23 (3) : 425-442.
Tobin, G.A. and B. E. Montz. 1997. Natural Hazards. The Guilford Press.
London. 388 pp.
UNDP. 1994. Strengthening Disaster Management Strategies in Thailand.
Asian Institute of Technology. Bangkok. 83 pp.
United Nations. 2002. Living with Risk. Disaster Reduction Strategy.
United Nations, Geneva. 382 pp.
Usher, A.D. 1994. After the forest. Thai Development Newsletter. 26 : 2032.
WHO. 2002. Environmental Health in Emergencies and Disasters. A
Practical Guide. Marketing and Dissem ation. WHO. Geneva. 205
pp.