The page presents a summary of the methodology and approach used to apply Coupled Model Intercomparison Project Phase 6 (CMIP6) datasets, in order to develop climate change projections for the 3S sub-basin.
Coupled Model Intercomparison Project (CMIP) is a project of the World Climate Research Programme (WCRP) providing climate projections to understand past, present and future climate changes. To date, there have been no detailed studies for the Mekong region under CMIP6. The Mekong River Commission (MRC) developed climate change scenarios for the Lower Mekong Basin (LMB) as part of their Climate Change and Adaptation Initiative (CCAI), based on CMIP5 datasets, and continue to apply these for their studies. Under CMIP5, 3 Global Circulation Models (GCMs) were selected by the MRC in 2014, which were identified as the most suitable for the Mekong region, as presented in Section 2.4.1. These are GFDL-CM3 (wetter overall), GISS-E2-R-CC (drier overall) and IPSL-CM5A-MR (wetter wet seasons and drier dry seasons).
The three GCMs selected in this study are indicated in blue (upper=wetter in all seasons), red (lower=drier overall, especially in wet season), orange (medium=increased seasonal variability, wetter wet seasons and drier dry seasons)
CMIP6: scenarios are called Shared Socio-economic Pathways (SSPs). These scenarios characterize possible future development pathways and there are 4 scenarios widely used: SSP126, SSP245, SSP370 and SSP585
CO2 emissions in comparable CMIP5 and CMIP6 scenariosCMIP6 datasets, as used on IPCC Assessment Report 6 (2021) – developed by ICEM – have been applied for the 3S sub-basin climate change projections. CMIP6 scenarios are called Shared Socio-economic Pathways (SSPs). These scenarios characterize possible future development pathways. There are 4 scenarios widely used: SSP126, SSP245, SSP370 and SSP585. The selection of a suitable projection for the 3S has followed these steps:
For the purposes of the 3S Joint Project, the CMIP6 GFDL-ESM4 model and SSP3-70 pathway has been adopted by ICEM for climate projections in the 3S. SSP3-70 is a middle-upper pathway associated with medium-to-high radiative forcing. It is a risk scenario, representative of projected LMB development with limited climate change mitigation/adaptation interventions. The GFDL-ESM4 SSP3-70 projection illustrates increased seasonal variability – wetter wet season and drier dry season.
More detailed future studies for the 3S sub-basin and LMB as a whole, should aim to develop more detailed statistical climate models, based on under CMIP6 scenarios.