Phuket, a key urban center in Southern Thailand, spans 539.67 km². Geographically, its coor-dinates are between 7°45' N and 8°15' N latitude, and 98°10' E and 98°30' E longitude. Figure 1. Phuket is the largest island in Thailand, located in the western part of the southern region in the Andaman Sea, Indian Ocean. It is approximately 700 km from Bangkok. The topography of Phuket is an island that lies from north to south. 70% of the area is mountainous. The highest peak is Khao Mai Thao Sip Song, which is 529 m high and is located in the south of Phuket Island, near Patong Beach. 30% of the area is flat, located in the southeast of the island in Mueang Phuket. This flat area is vast (Ufimtsev, 2011). Historically, Phuket was a major agricultural and tin mining area in Thailand. However, much of the land has now transformed into business districts and residential areas (Moukomla & Marome, 2025). Near the plains lies a large indented coastline, Chalong Bay, which features a mangrove forest at the estuary of Phuket province. To the north of Phuket, a narrow strait called Pak Phra Strait connects the island to the mainland via the Thao Thep Krasattri Bridge and Thao Si Sunthon Bridge. The western part of Phuket is characterized by mountains stretching from north to south, interspersed with narrow coastal plains (Akkajit et al., 2024). This coastline is famous for its beautiful white sandy beaches, including Mai Khao Beach, Nai Thon Beach, Bang Tao Beach, Kamala Beach, Patong Beach, Karon Beach, Kata Beach, and Kata Noi Beach, in sequential order (Akkajit et al., 2021). Patong Beach is the largest and attracts both Thai and international tourists throughout the year.

Since the central part of Phuket Island is a mountainous area and undulating plain, the drainage system is a radial drainage pattern. In the study area, there are 3 drainage patterns from the center: flowing direction to the north, flowing direction to the west, and flowing direction to the east. The stream with a flow direction to the north is found as Khlong Dan Yit stream only in the Nai Yang beach area in the north of Phuket. Stream flowing west of Phuket has 7 important watersheds: The northernmost basin has the main river, Khlong Phama Long. The basin in the Bang Thao beach coastal plain, which is the largest plain in Phuket, has a watershed system with important waterways, namely Khlong Riang, Khlong Thalang, and Khlong Bang Cho, where the three rivers merge to become Khlong Phang before flowing into the sea at Bang Thao Beach. Khlong Bang Thao is a short river in the south of Bang Tao Beach. The basin in Kamala beach has only one Khlong Kamala stream flowing into the sea (Pakoksung et al., 2022). The basin in Patong beach has only one Khlong Patong stream flowing into the sea. The basin in Karon and Kata beach has a short but unnamed river flowing into the sea as well. In the southernmost basin, at Nai Han beach, there is only one stream, Khlong Ya Yai, flowing into the sea.

Stream flowing east of Phuket has 8 important watersheds: Khlong Tha Nun stream is a water-shed in the northern part of Phuket. The eastern watershed system in the Khao Phra Thaeo Non-hunting area has Khlong Bang Sai and a short unnamed stream flowing into the sea. Khlong Tha Ruea originates from Kuan Wa Hill and flows into Khlong Ko Kaew.

The headwaters are at Khao Phra Thaeo Hill. The two canals meet to become Khlong Ko Kaew, flowing into the sea near Yamu Cape. Khlong Chang Phan Lang is a short waterway flowing into the sea near Khlong Ko Kaew. Phuket town is the second largest plain on Phuket Island. There is an important watershed system, Khlong Bang Yai, which originates from important rivers in the Kuan Wa Hill and Khao Mai Thao Sip Song mountains, which are the largest mountain ranges in the central part of Phuket (Kulsoontornrat & Puangkaew, 2025). It is the source of important streams, Khlong Kathu Waterfall and Khlong Bang Thong, which flow together to form Khlong Ket Ho, becoming Khlong Bang Yai and flowing into the sea at Sapan Hin Cape. The other three river basins in the south of Phuket Island originate in Khao Mai Thao Sip Song, namely Khlong Chalong, Khlong Fai Mai, and Khlong Sai Yuan, which flow into Chalong Bay.

This study assessed flash flood susceptibility using secondary data acquired from a variety of sources, especially data on flash flood areas that occurred during 2024-2025 from the National Hydroinformatics Data Center and Geo-Informatics & Space Technology Development Agency (Public Organization). Spatial data for the analysis of factors affecting flash flood occurrence include Elevation, Slope, SPI, STI, TWI, SF, DD, IN, Mean annual precipitation, Geology, Distance to stream, Distance to road, and Land use. As detailed in Table 1, these data represent crucial variables used for evaluating areas prone to flash floods. All spatial data will be generated in raster format with grid cell size of 50 × 50 m.

The methodology of this research followed these steps: (1) flash flood area analysis, (2) spatial database analysis of driving factors, and (3) statistical approach. Figure 2 illustrates the specifics of each step, which are detailed below.

The topography of Phuket Province, which is an island, has a large mountain range in the middle of the island and a narrow plain. Whenever a thunderstorm occurs, the mass of water flows into the canals in Phuket, and is quickly drained into the sea. However, at present, this is not the case. In other words, flash floods occur in many communities, and the water is drained into the sea slowly, due to the structures that block the drainage, resulting in flood disasters in many places on Phuket Island. The results of the analysis of flash flood areas in Phuket found that in the past 2 years (2024-2025), Phuket has experienced major flash floods in 10 years. In the study area, there were 14 flash flood disaster areas, covering a total area of 52.245 km² Figure 5. Most of the flash floods occur in the plains near the foothills of the island around Phuket Island. The areas where flash floods occur regularly in Phuket are as Figure 5.

Zone A covers the northern part of Phuket Island, along Mai Khao Beach and Nai Yang Beach. In Nai Yang Beach, flash floods are often experienced around Sakhu Subdistrict Administrative Organization and along the main canal, Khlong Phama Long Stream. In Mai Khao Beach, flash floods are often experienced north of Phuket International Airport.

Zone B covers the area between Thalang District and Choeng Thale Subdistrict, namely where Khlong Riang meets Khlong Thalang to become Khlong Phang. These river basins are often the catchment area for water coming from the Khao Phra Thaeo mountain range, resulting in flash floods around Thep Kasattri Subdistrict Municipality Office.

Zone C is the southern part of Choeng Thale Subdistrict, where Khlong Bang Thao flows from the central mountains of Phuket. This area is prone to flash floods due to its location at the foot of a piedmont hill, causing damage from flooding in the surrounding areas of Choeng Thale Sub-District Administration Organization. Water regularly cuts off major roads such as Srisoonthorn Rd. and Bandon Choeng Thale (Highway 4030).

Zone D has experienced flash floods in the northeastern part of Phuket Island in the Pa Khlok Sub-district. Zone E covers the eastern part of Phuket Island between Si Sunthon and Ko Kaew Sub-districts. This area is prone to flash floods because it receives water from two mountain ranges, Khao Phra Thaeo and Kathu Hill, causing the water to flow into Khlong Ko Kaew, Khlong Tha Ruea and Khlong Bang Sai Stream. This area is prone to flooding on Highway 402 and surrounding communities every year.

Zone F covers Kamala Beach. This area is often flooded, just like Zone G in Patong Beach. Both zones receive water from Kathu Hill that flows into tourist areas regularly. Flash floods are common along the Patong and Kamala Stream canals.

Zone H and Zone I are Karon and Kata Beaches, which are also areas that experience flash floods but have not sustained any damage.

Zone J is an area affected by widespread flash floods, and the impacts are severe. The affected areas include the entire Mueang Phuket District, due to the accumulation of water from many canals, the terrain is steep and is a ravine that receives water from the mountain range, becoming important canals, namely Khlong Bang Thong and Khlong Kathu Stream, which flow into Khlong Ket Ho and Khlong Yai Stream. The major flash floods on June 29-30 and July 7-8, 2024 caused widespread damage in Phuket's Old Town. There are also major damaged zones along the eastern coast of Phuket Island, namely Zones K, L, M, and N, which include Ratsada, Wichit, Chalong, and Rawai Sub-districts.

From the analysis of 13 driving factors, which are important factors affecting the susceptibility to flash floods, when analyzed using the logistic regression statistical process together with the flash flood area data, the results of the study are as shown in Table 2. In this study, each factor has been shown to have an influence on the susceptibility to flash floods with the statistical value β, that is, if β of that factor is shown as a positive value, it means that the higher the value of that factor, the more susceptible it is to flash floods Conversely, a negative β value for a factor indicates that lower values of that factor increase flash flood susceptibility. The Relative Operating Characteristic (ROC) curve indicates the regression equation's effectiveness in predicting sinkhole risk areas based on probability. For the probability of sinkhole areas, the ROC value was 0.822 Figure 6, which is a high value because the value is close to 1.00, indicating that all 13 factors are very effective in analyzing areas at risk of flash floods.

All variables were significant at the p < 0.01 entry and p > 0.02 removal levels. ROC relative operating

The results of this research found that, the areas susceptible to flash floods have factors that show positive β values, consisting of 6 variables: TWI, IN, Slope, DD, STI, and Distance to road. The factors that show negative β values are 7 variables: SF, SPI, Land use, Elevation, Mean annual precipitation, Geology, and Distance to stream. The Exp β value indicates the level of influence of the factors that affect the occurrence of flash floods, with high Exp β values being the factors that have the greatest impact on the occurrence of flash floods in the study area. When arranged according to the Exp β value, it shows the level of the factors that affect the occurrence of flash floods from most to least as follows: TWI, SF, DD, IN, Slope, Distance to road, Mean annual precipitation, Elevation, Land use, STI, SPI, Distance to stream, and Geology, respectively. The level of Exp β value of each variable is shown as follows: 3.412, 2.783, 1.214, 1.173, 1.079, 0.998, 0.961, 0.953, 0.945, 0.798, 0.732, 0.099, and 0.097, respectively Table 2.

The factor that affects the most vulnerability to flash floods in Phuket is TWI, which shows a high positive β value. It shows an Exp β value of 3.412, and a High positive β value of 1.537. These factors indicate that high TWI levels are areas with a high chance of water accumulation. In the study area, high TWI levels were found in the coastal plains of Phuket, including the northern part, which is the Mai Khao Beach market area, the central part of Phuket, which is the Thalang district, where the major waterways, Khlong Riang and Khlong Thalang, which receive water from Khao Phra Thaeo Hill, and along the eastern coast of Phuket. Especially in the Phuket Old Town area, which is located in the southeast of the island and the area around Chalong Bay, there are large high TWI areas. These areas are inevitably prone to water accumulation, resulting in flash floods. Currently, flash floods are common in these areas.

The SF factor is the factor that affects the occurrence of flash floods in the next level after TWI. It shows an Exp β value at 2.783 and a High negative β value at -1.212. The results of the study found that if the SF level shows a low value, it indicates that the area has a high runoff and tends to have a rapid runoff. In the study area, the SF level showed a low value along the Phuket mountain range, which is an area with a fairly steep slope and waterways around the mountain range, affecting the rapid flow of water in the river during thunderstorms.

The DD factor is the third influential factor. It shows an Exp β value at 1.214 and a positive β value at 0.795. The results of the study found that the area with DD > 3 appeared in two areas of the eastern coastal plain, namely Ko Kaeo Sub-district, which is the confluence of major rivers, namely Khlong Ko Kaeo and Khlong Tha Ruea. This area is often flooded because there are many tributaries. Another area is Phuket Town, which is the area where tributaries meet from the mountain range in the middle of Phuket Island. The major rivers that meet in the city area are Khlong Ket Ho and Khlong Bang Yai. And, Khlong Fai Mai and Khlong Chalong also found High DD level areas. The area with DD = 1 to 3 indicates a moderately drained watershed area. It appears around major rivers in Phuket Island, indicating that the steep terrain along both sides of the river is at moderate risk of flash flooding.

The IN factor is the fourth factor showing the sensitivity to flooding. It shows an Exp β value at 1.173 and a positive β value at 0.926. The study found that high IN indicates that water infiltrate to the ground at a low level (lower infiltration rates), resulting in higher runoff on the surface of the terrain. The high IN level is distributed in the downstream areas of each river basin, namely Khlong Phama Long, Khlong Tha Nun, khlong Phang, Khlong Bang Thao, Khlong Tha Ruea, Khlong Kamala, Khlong Patong, and the surrounding areas of Chalong Reservoir.

The Slope factor showed a positive β value of 0.921. The results of the study found that areas with high slopes will affect the susceptibility to flash floods, which will occur in the study area at the shoulder of the hill and the foot of the hill. The Distance to road factor is another factor that shows the level of Exp β value = 0.998, ranked 6th. This is a factor that occurs and is influenced by human actions. The study area showed that areas near the road tend to have accumulated flooding, and some areas have overflowing on the road, especially on roads that cut through the foot of the hill, which roads in Phuket tend to block the water mass.

The Mean annual precipitation factor and the Elevation factor showed negative β values at -0.032 and -0.046 respectively. It shows that the low rainfall distribution area is more susceptible to flash floods. This is because the southeastern area of Phuket Island is behind the mountain range and has many waterways flowing through it, making it an area that receives water flowing from the mountain range. This is different from the eastern coastal area along the entire length of Phuket Island, even though it is in front of the mountain, and is directly influenced by the southwest monsoon, but it results in less flash floods than the western coast. This may also be due to other factors. The topographic factor showed a negative β value.

It indicates that areas with an elevation of approximately 0-50 meters are susceptible to flash floods. The Land use factor showed a negative β value at the level of -0.055. This is because the land use type classification was set from 1-5, namely waterbodies, urban and built-up land, agricultural land, forest land, and beach and swamp, respectively. The negative β value can indicate that areas covered by waterbodies and urban and built-up land are susceptible to flash floods. In Phuket Province, there has been a wide expansion of urban areas, especially in the western and eastern coastal areas of the island, which are residential and business areas for tourism. Such areas often have structures encroaching on major canals. Some areas have built residences and resort hotels that obstruct natural waterways. Some have built such structures over canals or natural waterways. This results in flash floods and mudslides along mountainsides and foothills, posing a major problem for water management in Phuket Province.

The four factors that affect flash flooding in Phuket at the final level are STI, SPI, Distance to stream, and Geology, respectively. They are interrelated, STI is the driving factor that determines the movement of sediments along the river. This sediment will cause erosion and sedimentation. A high STI indicates high sedimentation and deposition in that area. SPI is the factor that causes erosion in the river. However, the study area showed a negative β value, which is still low in Phuket. The factors of Distance to stream, and Geology will support the first two factors. When flash flooding occurs, there is often a debris flow that deposits in the foothills of the study area. In particular, flash floods and sedimentation along both sides of the river and areas covered by Terrace and Fluvial deposits are often accompanied by alternating flash floods and sedimentation, when thunderstorms repeatedly hit the same area for a long period of time.

The findings of this study involve a flash flood susceptibility map for Phuket Province, devel-oped through the statistical analysis of logistic regression. The derived β values were instrumental in building a spatial database to aid in the management of flash flood events in Phuket. Figure 7. The study's findings were derived from analyzing spatial data within GIS, as outlined in Equation 8.

(8)

The β values derived from various factors in this research reveal the level of flash flood sensi-tivity as spatial data across Phuket. In particular, the classification of the level of sensitivity to floods is shown in 5 levels: very high sensitive areas, high sensitive areas, moderate sensitive areas, low sensitive areas, and very low sensitive areas, respectively Table 3.

In Phuket Province, areas with very high flash flood susceptibility level were found covering an area of 43.40 km² (8.04% of the total area). Most of them cover areas along major rivers in Phuket Island. The most obvious areas are the mountainous terrain with rivers flowing through, the foothills and the plains between the valleys (piedmont and intermontane) in the north of Phuket, which is the Thalang District and Kathu Sub-district. In addition, the coastal plains in the east of Phuket Island also have very high flash flood susceptibility level areas, distributed along major rivers in the Ko Kaew, Talat Yai, Talat Nuea, Wichit, Chalong, and Rawai Sub-districts.

The high flash flood susceptibility level area covers an area of 86.38 km 2 (16.01% of the total area). It has appeared in the area near the very high level continuously, the topography that has the characteristics of the foothills and coastal plains, such as the northern part of Phuket Island, Mai Khao Beach area. In the central part of Phuket Island, which is a plain between the valley and the foothills, such as Thep Krasattri, Choeng Thale, and Si Sunthon Sub-districts. And, the topography along the eastern coast of Phuket Island, Ko Kaew, Ratsada, Talat Yai, Talat Nuea, Wichit, Chalong, and Rawai Sub-districts.

As for the narrow plains on the western coast of the island, there are high flash flood susceptibility level areas in important tourist areas, such as Kamala, Patong, Karon, and Kata. The Medium flash flood susceptibility level area covers an area of 121.27 km 2 (22.47% of the total area). It has appeared along the coastlines of both the western and eastern parts of the island and the pied-mont. Low and very low flash flood susceptibility levels mostly cover the mountain ranges of Phuket, which cover more than 50 percent of the island.

Urbanization in coastal tourist city areas without concrete planning has resulted in the city being at risk of flash floods and landslides. The expansion of the city in any direction has caused the infrastructure system to be disorderly, especially the sewage system built after the expansion of the city. If thunderstorms last for a long time, flash floods are inevitable. Moreover, the current climate change has resulted in the rain patterns in Phuket in 2024-2025 that are more frequent and longer lasting.

This is similar to major cities around the world that are experiencing frequent flash flood disasters along coastal areas, such as Madhya Pradesh (Nandam & Patel, 2025), Surat, Mumbai, Chennai, and Kolkata in India (Dhiman et al., 2019), Haikou (Luo et al., 2024), Zhuhai (Zhong et al., 2024) and Xiamen City in China (Xu et al., 2025), Cap-Haïtien City in Haiti (Jean Louis et al., 2024), and North-West Galala City in Egypt. Therefore, researchers need to find tools and methods to study and assess flash flood susceptibility in the most accurate spatial data.

Phuket is a coastal tourist city without systematic urban planning. Urban and built-up land has expanded rapidly and directionless. Buildings such as houses and resorts have encroached on natural waterways. Moreover, some areas have been built over natural streams, causing natural waterways to change their course. In addition, buildings in Phuket often have small and narrow drainage pipes, which often cause flooding in Phuket during thunderstorms. This is different from large cities that have built drainage systems with networks of water drainage to the sea quickly, such as Guangdong in China (Chen & Huang, 2024)), Chennai (Andimuthu et al., 2019), and Norfolk in the USA (Barbosa et al., 2025).

From the statistical analysis of logistic regression, which is a popular statistical method used in studying flood disasters in Phuket, it shows the factors that affect the occurrence of flash floods effectively (Allegri et al., 2024). The results of this research show the values of the fac-tors that influence the occurrence of flash floods with β value. This research show that the factors that affect the occurrence of flash floods in Phuket from most to least are as follows: TWI, SF, DD, IN, Slope,

Distance to road, Mean annual precipitation, Elevation, Land use, STI, SPI, Distance to stream, and Geology, respectively. It is consistent with the Rheraya watershed in Morocco, stating TWI and DD factors have the most influence on flooding, but the difference is the Distance to stream factor that the research has a low influence on flooding (Elghouat et al., 2024). However, in Tetouan, it was found that the rainfall factor had the most influence, even though it is also in Morocco (Sellami & Rhinane, 2024). In terms of flash flood susceptibility assessment in northeastern Bangladesh and Tafresh Watershed in Iran, it was found that rainfall and slope factors have the greatest impact on flash flood occurrence in these areas ((Islam & Chowdhury, 2024); (Janizadeh et al., 2019)), which is different from this research.

Between 2022 and 2024, Phuket experienced major flash flood disasters. The majority of the affected areas were lowlying urban regions, specifically Thalang, Phuket Old Town, Ko Kaew, and Choeng Thale Figure 8. Consequently, this research collected the locations of flash flood occurrences during that period to validate the results obtained from the logistic regression model. The sampling of flash flood location data utilized 183 realworld, ground truth flood locations (97 flood samples and 86 non flood samples).

The validation was performed using the Accuracy Assessment method (Chen et al., 2024). This methodology involved the use of the 'tabulate area' command within the Geographic Information System (GIS). The results from the model validation demonstrated an overall accuracy of 86.89% and a Kappa coefficient of 0.74, indicating that the model's performance is highly satisfactory Table 4.

During the monsoon season, flash floods in Phuket often occur during June-September of each year. However, such disasters are only reported in news reports about flood affected areas and specifying the areas in writing. The relevant government or private agencies have no proactive disaster prevention and mitigation policies. There is only a defensive response to disasters, that is, when a disaster occurs, they go to help the victims, alleviate suffering by providing relief supplies to the victims, and repair the infrastructure damaged by the disaster, etc., which is done every year. However, the spatial data showing the risk areas showing each level of flash flood susceptibility at the provincial or local level that should be displayed in the form of a map, was never found in this research area. If searching for information online about the flood disaster in Phuket, it was found that there was no map showing the susceptibility of flash floods in Phuket to warn villagers to be careful during the period of prolonged thunderstorms. This research gathered and analyzed flash flood related factors to produce a map illustrating Phuket's flash flood susceptibility levels. The results of this study will be useful for government agencies and private sectors, as well as local communities in sensitive areas. Figure 9 shows the areas with the high and highest flash flood susceptibility in urban areas and important economic districts. This is a preparation for dealing with climate change events that cause flood disasters to occur more frequently, so that Phuket can become a coastal tourist city that is ready to deal with flash flood disasters sustainably.

This research has certain limitations and presents avenues for future improvement. Firstly, a key challenge was the difficulty in acquiring data on actual flood events in Phuket using re-mote sensing techniques. This study did not incorporate such data because flash floods typically occur during the monsoon season, which hinders passive remote sensing satellites from ac curately recording the real-time flood extent. Consequently, future work may need to integrate active remote sensing satellite techniques for research applications in Phuket or other study areas situated within monsoon affected regions. Secondly, the research findings identified a total of 13 variables influencing flash flood susceptibility. It was found that the top three vari-ables (Topographic Wetness Index, Stream Frequency, and Drainage Density) exhibited the highest susceptibility in areas characterized by foothills extending into coastal plains, particularly on islands featuring a high mountain range in the center. However, future research or applications leveraging this methodology should adjust certain variables to align with the specific geographical conditions of each locality. Finally, given that flash flood hazards are increasing in frequency due to current climate change, responsible governmental and private sector agencies should prioritize research and the development of comprehensive flash flood hazard maps for each subwatershed. This should be coupled with the establishment of realtime water level monitoring stations. These measures are crucial for preparedness and for ensuring a timely response to potential flood events, thereby safeguarding the lives and property of local populations.