Nature-based solutions for flood risk mitigation under climate change and land use change in the Pasak River Basin, Thailand | |
| Author | Piyanuch Nontikansak |
| Call Number | AIT Diss. no.WM-24-01 |
| Subject(s) | Flood damage prevention--Thailand--Pasak River Basin Climatic changes--Thailand--Pasak River Basin Land use--Thailand--Pasak River Basin |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Engineering in Water Engineering and Management |
| Publisher | Asian Institute of Technology |
| Abstract | Climate change affects certain components of the hydrological cycle, especially precipitation, which causes changes in the flood regime both temporally and spatially. These uncertainties, related to changes in precipitation and flood patterns, may influence flood management in the future. As a result, the concept of nature-based solutions is attracting more adoption to alleviate flooding in European countries. It is not only beneficial for flood mitigation but also reduces impacts and vulnerability to climate change. Unfortunately, the concept of nature-based solutions for flood mitigation and the impact of climate change have not received much attention in Thailand. This research attempts to apply this concept to the Pasak River Basin in Thailand. The basin is a climate-vulnerable area and is also susceptible to flooding. Additionally, this area is experiencing land use change where agricultural land has encroached on forest land. Therefore, this study aims “to assess the effectiveness of nature-based solutions for flood risk mitigation under climate change and land use change, with a focus on the case study area of Bueng Sam Phan District, Petchabun Province”. To enhance long-term flood mitigation and climate adaptation planning, a combination of both top-down and bottom-up approaches has been embraced. The top-down approach involves a comprehensive impact assessment, drawing upon scientific knowledge, statistical analysis, and various models to pinpoint flood-prone areas under dynamic climate and land use changes. Naturally, this assessment begins by projecting future climate conditions. We utilized five CMIP6 global climate models across two Shared-Socioeconomic Pathways (SSP2-4.5 and SSP5-8.5) to project precipitation, maximum and minimum temperatures across the basin. The findings indicate that the basin is expected to warm by 3-4 °C, with annual rainfall increasing by 2-5% under SSP2-4.5, and twice that rate under SSP5-8.5. Changes in climate variables can significantly impact the hydrology alteration on the Pasak River, the main river within the basin.As mentioned above, land use change is also an important factor that affects flood regimes. For this reason, we chose the SWAT model to assess the impacts of these two factors on hydrological alteration in the Pasak River. Before proceeding with the assessment, we prepared a future land use map as input for the model. Future land use change was predicted using the Dyna-CLUE model. Two scenarios were considered for predicting land use change: historical trends and conservation scenarios. The conservation scenario was created to demonstrate the benefits of reforestation, one of the NBS interventions considered in this study. Hydrological alterations in the river were evaluated under the individual and combined effects of the two factors using the Indicator Hydrologic Alteration (IHA). The analysis indicated that climate change is a major driver of increasing the magnitudes and shortening the durations of high-flow pulses, small and large floods, in conjunction with land use change. On the other hand, both factors have little effect on the timing of occurrence of those hydrological parameters. In all simulations of the individual and combined impacts, the severity of flooding is likely to increase significantly due to the combination of climate change under SSP5-8.5 and land use change under historical trends. To illustrate areas vulnerable to these impacts, flood hazard and risk maps were generated using MIKE FLOOD. These maps serve as vital tools for proposing appropriate flood mitigation measures in specific areas. The 10-year and 100-year floods for both the individual and combined impacts of climate change and land use change were estimated to identify the worst-case scenario for further assessing the effectiveness of the proposed measures. The simulations revealed that the combination of climate change under SSP5-8.5 and land use change under historical trends results in the most extensive inundation compared to other scenarios. The affected area encompasses Nong Jaeng, Bueng Sam Phan, and Gun Chu subdistricts, covering 47 km² for the 10-year flood and 52.54 km² for the 100- year flood. This represents an increase of approximately 45% and 26.3% compared to the baseline event, respectively. The maximum flood depths reach 4.33 meters for the 10-year flood and 5.58 meters for the 100-year flood. According to the flood maps, the floods in this area are classified as fluvial floods. The inundation occurs due to excessive water levels from the Pasak River. Therefore, the proposed NBS measures selected to mitigate the floods include reforestation, widening of the Pasak River channel, and natural bypasses. The first NBS was proposed with the main objective of maintaining environmental balance, while the latter two NBSs were chosen for their capacity to increase drainage capacity. However, it's important to note that a single NBS may not be sufficient to manage flooding in this area. Thus, the combinations of each NBS were also evaluated.The results indicate that the combination of all proposed NBS measures can effectively reduce flood risk in the BSP area by up to 90% for small floods (10-year return period) and by more than 50% for large floods (100-year return period). Nonetheless, this is solely the technical assessment conducted based on scientific knowledge. Awareness and commitment from local stakeholders are paramount for flood hazard mitigation and climate change adaptation. Therefore, the results of this study were presented and discussed with stakeholders through focus group discussions. Additionally, participants were required to complete a questionnaire to provide insights into their backgrounds and express their opinions and concerns. It can be concluded that the majority of stakeholders expressed agreement with the proposed NBS, although they did express concerns regarding the construction of the bypass, such as the need for approvals from relevant government agencies and budget allocation from the central government. The findings of this study offer valuable input for making risk-informed decisions regarding flood hazards in the context of climate change and socioeconomic development pressure. Furthermore, this study recommends the implementation of nature-based solutions, which are resilience-oriented measures, for sustainable flood risk management. |
| Year | 2024 |
| Type | Dissertation |
| School | School of Engineering and Technology |
| Department | Department of Civil and Infrastucture Engineering (DCIE) |
| Academic Program/FoS | Water Engineering and Management (WM) |
| Chairperson(s) | Shrestha, Sangam |
| Examination Committee(s) | Shanmugam, Mohana Sundaram;Ho, Huu Loc;Virdis, Salvatore G.P. |
| Scholarship Donor(s) | AIT-BNU-Thai Pipe PhD Scholarship |
| Degree | Thesis (Ph.D.) - Asian Insitute of Technology, 2024 |