Agriculture Adaptation Options for Flood Impacts under Climate Change—A Simulation Analysis in the Dajia River Basin

Adaptation to climate change has become an important matter of discussion in the world in response to the growing rate of global warming. In recent years, many countries have gradually adopted adaption strategies to climate change, with the aim of reducing the impact of climate variabilities. Taiwan is in a geographical location that is prone to natural disasters and is thus very vulnerable to climate change. To explore an appropriate method for Taiwan to adapt to climate change, this study took Dajia River Basin as the simulation site to explore the potential climate change impact in the area. An impact study was conducted to identify the trend of flooding under climate change scenarios. We used the SOBEK model to simulate downstream inundation caused by the worst typhoon event of the 20th century (1979–2003) and for typhoon events that might occur at the end of the 21st century (2075–2099) in Taiwan, according to the climate change scenario of representative concentration pathways 8.5 (RCP8.5) and dynamical downscaling rainfall data. Agricultural lands were found to be the most affected areas among all land types, and the flooded area was forecast to increase by 1.89 times by the end of 21st century, when compared to the end of 20th century. In this study, upland crops, which are affected the most by flooding, were selected as the adaptation targets for this site and multiple engineering and non-engineering options were presented to reduce the potential climate change impacts. With respect to the results, we found that all adaptation options, even when considering the cost, yield higher benefits than the “do-nothing” option. Among the adaptation options presented for this site, utilizing engineering methods with non-engineering methods show the best result in effectively reducing the impact of climate change, with the benefit-to-cost ratio being around 1.16. This study attempts to explore useful and effective assessment methods for providing sound scientific and economic evidence for the selection of adequate adaption options for flood impacts in agriculture in the planning phase.