Projection of future precipitation extremes across the Bangkok Metropolitan Region

There is a pressing need to develop local-scale climate projection profiles for supporting climate impact assessments. This study contributes plausible future precipitation scenarios for the Bangkok Metropolitan Region (BMR), which builds on the existing evidence base that projects increasing future precipitation. Meteorological data sets from 16 stations located within the BMR and nearby provinces were used for bias correcting five regional climate model scenarios, and future extreme indices were graphed and spatially interpolated to interpret how precipitation extremes may develop to the end of the 21st century. Results indicate that over the coming century, total annual rainfall will increase, with the volume and number of days with heavy/very heavy rainfall also increasing. Total monthly and monthly heavy/very heavy rainfall are projected to increase in the late monsoon, and monthly five-day cumulative and one-day maxima project higher amounts of late monsoonal rains. Spatial interpolation of selected indices indicate substantial projected increases in extreme rainfall across the BMR, with its northern part receiving the heaviest amounts of precipitation. In comparison to the past period (1980-2009), over the long-term (2070-2098) the total monthly heavy/very heavy precipitation during October is projected to increase by 100-120% over Pathum Thani province and 80-100% over the remainder of the BMR. Together with the study's associated R and Python scripts, this study aims to provide an open and reproducible approach to deriving plausible future projections of climate variables at the city scale.