Floods and demographics in Thailand, 2005-2019

Abstract In Thailand, where floods have occurred frequently, it is possible that economic development and population growth in recent years change the way people interact with flood and the way people move when floods occur. In this study, we analyzed the recent (2005–2019) relationship between flooding and population distribution across Thailand to contribute to the planning of adaptation measures to minimize the flood damage caused by climate change. First, the population distribution point data produced by Oak Ridge National Laboratory were used to analyze trends in population movement and distribution from 2009 to 2019, by examining whether the population size at each point throughout Thailand was greater than, less than, or the same as the estimated value. The results suggest that the 2011 and 2017 floods respectively caused the temporary migration of people to areas that were not inundated or to the Bangkok metropolitan area. They also suggest that people’s response to floods changed after the 2011 floods which is said the worst flood in the Thai history. Next, the relationship between the number of points indicating a smaller-than-estimated population and the flood information in the previous year were examined. The flood information includes the inundated area, the number of deaths caused by flooding, and precipitation information. The size of the inundation area had a significant impact on the population decline, especially with correlation coefficients of r = 0.426 for the north and r = 0.501 for the northeast. Similarly, the number of deaths by flooding in the previous year led to a population decline in the following year. However, precipitation in the previous year did not account for the population decline in the following year. Therefore, it is inferred that demographics after floods have regional characteristics and Thai people in recent years are shifting from a lifestyle that included living in harmony with floods to an avoidance of inundation, mostly in local urban areas and Bangkok metropolitan area.