Regional-scale flood impacts on a small mountainous catchment in Thailand under a changing climate

Abstract

Extreme rainfall and flooding are common during the summer monsoon season in Thailand. In this study, we utilized Robust Empirical Quantile Mapping (RQUANT) to correct the bias in precipitation, and total runoff data obtained from the latest Couple Model Intercomparison Project phase 6 (CMIP6) for the upper Lam Takong river basin. Five different methods were employed to estimate the river discharge and four estimations based on Budyko functions. Our analysis revealed that the ‘Total runoff’ method yielded the most accurate representation of the observed discharge. Impacts of change in land use are examined in terms of compound roughness. The Multi-Model Ensemble (MME) precipitation under medium-emission (SSP2-4.5) and high-emission (SSP5-8.5) scenarios is projected to increase by 5.74 and 10.91%, respectively. Correspondingly, the discharges are expected to increase by 4.57 and 11.05% for the far-future periods. In general, the Flo-2D model satisfactorily simulated the water level in the main channel but it underestimated small inundation depth (<0.5 m) across the floodplain. Comparing inundation maps among different scenarios and timelines, changes in the inundation area were relatively small (0.05%), especially when compared to changes in floodplain storage (6.85%) due to the mountainous nature of the river basin. HIGHLIGHTS Utilizing the internal variable from the CMIP6 database to create inputs to flood simulation model.; Investigation of the functional form (aridity index) for the small mountainous river basin.; Selection of suitable observed data from several world databases.; Investigating the well-known bias correction method (RQUANT).; Examining the flood mitigation measures for this particular small mountainous river basin.;

Keywords

• bias correction
• cmip6
• flo-2d
• flood simulation
• shared socioeconomic pathway