Floods, and especially large-scale floods, are frequent in Thailand, resulting in considerable property damage, injury, and loss of life. However, as rivers are an important source of water, including for agriculture, local populations have chosen to remain in areas at risk of flooding by developing measures to cope with floods (Phanthuwongpakdee 2016). Traditional flood mitigation measures include the selection of micro elevations, channel excavation, and construction of stilt houses and earthen mounds (Iwaki 2016), all of which recognize the characteristics of floods in Thailand, where many rivers have gentle gradients, water levels rise slowly during flooding, and inundation is not rampant. These characteristics stand in contrast to those of flooding in Japan, for example, where many rivers flow swiftly and heavy rains are frequent, such that the intervals between inundations are short.
Rapid population growth in Thailand since the beginning of the 20th century has led to the expansion and greater density of urban areas and to increased socioeconomic development. Extensive road construction, the widening of existing roads, and an increasingly westernized lifestyle in Thailand have been accompanied by declines in the numbers of stilt houses and earthen mounds in rural areas (Iwaki 2016). Instead, the government has constructed levees and causeways, reflecting a shift from an emphasis on relatively small-scale control measures that allow local populations to live with floods to larger-scale measures. However, the latter are far from sufficient, as construction has not kept pace with faster-than-anticipated growth and effective planning has been hindered by the country’s political turmoil. The changes in demographics and the government’s approach to flood control may lead to significant changes in the way in which Thai people deal with floods and their choice of where to live.
Through the analysis of global examples of disasters such as nuclear accidents, forest fires, and heat waves, Karácsonyi and Taylor (2021) concluded that seven factors explain the complex and diverse links between populations and disasters: population impacts, vulnerability, mass relocation, spatial and regional approaches, climate change, urbanization, and response methods.
Bangladesh provides an example of a country-specific relationship between population dynamics and disaster. In Bangladesh, floods cause short-term, but few long-term, population movements, in contrast to agricultural crop failures (Gray and Mueller 2012). An econometrics analysis detected no significant long-term impact of three types of natural disaster (earthquakes, tornadoes, and hurricanes) on population density increases in the U.S. counties (Wang 2019). Mizutani (1989) studied the factors driving population declines in disaster areas in Japan, including quantitative relationships, and the population recovery process. Inoue et al. (2021) compared the population structure and future population estimates in an area of expected inundation in Mabi-Cho, Kurashiki City, Okayama Prefecture, Japan, with nationwide data, finding a significant decrease in population density in the expected inundation area relative to non-inundation areas nationwide.
The tracking of macro population dynamics after disasters has been facilitated by the use of cell phone SIMs and location-based services (Bengtsson et al. 2011; Yabe et al. 2020). Observations of the movement trajectories of cell phone users before and after five large-scale disasters in the U.S., Puerto Rico, and Japan showed that population recovery patterns can be approximated by a common negative exponential function (Yabe et al. 2020).However, in a review of 83 research papers, Thompson et al. (2017) found that far fewer studies have examined the relationship between floods and evacuation than have addressed the relationship between hurricanes and cyclones and evacuation. The one paper in their sample that focused on Thailand examined the relationship between tsunamis and evacuation (Thompson et al. 2017).
The 2011 floods in Thailand were the worst in the country’s history, with damage occurring in 61 provinces. A recent study of floods and demographics in Thailand involved comparison of the results of a nationwide analysis of household evacuation responses in 2011 with those of a partial analysis focusing on Ayutthaya Province (Bhula-or et al. 2020). Household evacuation decisions were shown to depend on a complex and diverse set of factors; specifically, vulnerable groups, such as women and elderly individuals, but also individuals with more assets and more stable employment, were less likely to evacuate, whereas households with reduced opportunity were more likely to evacuate to avoid loss and death (Bhula-or et al. 2020). In a study of the relationship between floods and demographics on a regional scale, rural poor families living in flood-prone areas were shown to have remained for generations, not because of any advantage conferred by staying, but rather because of the difficulty of moving due to economic factors and the high ratio of elderly individuals in this population (Tahira et al. 2015).
Analyses of the relationship between flooding and population dynamics must take into account the demographic characteristics of areas at risk of future large floods to enable the development of disaster prevention and evacuation plans. However, few such studies have been conducted in Thailand. Kiguchi et al. (2021) analyzed the effects of climate change and adaptation measures in Thailand, and found that most climate models showed an increasing trend in the national average precipitation in the future (2080–2099) compared with the baseline period (1980–1999). Given the increases in urbanization and densification in the country, heavy rainfall events and subsequent large-scale floods will likely cause more damage and affect a larger proportion of the population. Studies of whether the Thai approach of “living with flooding” will continue to be possible or desirable, and of whether the lifestyle and mobility patterns of Thai people are changing to avoid floods, are thus needed.
Thus, the objective of this study was to examine the recent (2005-2019) relationship between flood and population dynamics in Thailand, including regional characteristics and the impacts of recent lifestyle and socioeconomic changes.