Assessing the impact of climate change on rainfall erosivity using CMIP6 in the Upper Nan Watershed, Thailand

Soil erosion is a critical environmental and agricultural problem in northern Thailand, and rainfall erosivity is a key driver. This paper evaluates projected rainfall erosivity in the Upper Nan Watershed, northern Thailand, using 10 general circulation models (GCMs) from the Coupled Model Intercomparison Project Phase 6 (CMIP6) across 3 Shared Socioeconomic Pathways (SSP; SSP1-2.6, SSP2-4.5, and SSP5-8.5) for the 2030s, 2050s, 2070s, and 2090s. The quantile mapping technique was used to transform CMIP6 output data into daily meteorological data required for rainfall erosivity studies. Monthly rainfall erosivity was computed as the sum of the rainfall erosion index (EI 30 ) of all storms that took place during a given month in the study area. This study used the relationship between monthly precipitation and rainfall erosivity to predict monthly rainfall erosivity under climate change. The results show that rainfall erosivity will increase in all 4 time periods, in each of the SSP scenarios from CMIP6. For the ensemble means of basinwide rainfall erosivity, the increase is expected to range from 3.9-26.5% compared to the baseline period (1986-2014). Long-term multi-model ensemble projections indicate that erosivity is expected to increase by 3.9-5.4% in the 2030s, 7.1-8.8% in the 2050s, 8.0-15.0% in the 2070s, and 9.9-26.5% in the 2090s. However, future rainfall erosivity estimations associated with different GCMs carry some uncertainty. Both monthly and annual peaks indicate important periods of potential erosion in the study area and are associated with increased precipitation induced by climate change, contributing to the increasing potential for rainfall-induced erosion in the study area.