Watershed vulnerability assessment in the context of climate change, land use change, and water use change in the Nan River Basin, northern Thailand

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This study assesses the watershed vulnerability of Thailand's Nan River Basin (NRB), encompassing both Upper and Lower NRB, under future climate change, land use changes, and water use variations. Using top-performing general circulation models (GCMs) from CMIP6, two shared socio-economic pathways (SSP2-4.5 and SSP5-8.5) are analyzed. Projections indicate increased precipitation and temperatures. Land use changes were modeled using the Dyna-CLUE model for business-as-usual (BAU) and rapid urbanization (RU) scenarios. Urban areas are projected to expand by 1.39% (BAU) and 7.49% (RU), forest areas by 33.43% (BAU) and 18.35% (RU), while agricultural land decreases by 40.13% (BAU) and 45.21% (RU). Water use projections show reductions in agricultural and domestic water use by 24.04 and 13.26%, respectively, with industrial use increasing by 212.73%, leading to a 20.82% overall reduction. Vulnerability assessments for 17 sub-basins reveal low vulnerability in the near future, escalating in the mid and far future due to changes in climate, land use, and water use. Sub-basins 10 and 12 are most vulnerable under SSP2-4.5, while sub-basins 4, 5, and 14 are critical under SSP5-8.5. These findings highlight the need for climate resilience, adaptive land use, and improved water management to ensure sustainability in the NRB.

• Identified top-performing CMIP6 general circulation models (GCMs) for the Nan River Basin (NRB) using quantile mapping bias correction.

• The 17 sub-basins in the NRB show low vulnerability until 2040, but this increases in subsequent decades due to intensified climate change, impervious area changes, and water use shifts.

• This study highlights assessing sub-basin vulnerability for resource prioritization and proactive planning.