Assessment of Future Droughts in Vietnam Using High-Resolution Downscaled CMIP6 Projections

This study investigates drought conditions in Vietnam and its seven sub-climatic regions using the Standardized Precipitation-Evapotranspiration Index (SPEI). SPEI was derived from daily, high-resolution (10-km) precipitation and temperature products from the CMIP6-VN dataset, which statistically downscaled CMIP6 global models. Performance evaluation of 22 CMIP6-VN models confirmed their accuracy in representing precipitation and temperature characteristics for the reference period (1985–2014). Regarding the future period (2015–2099) under three Shared Socioeconomic Pathways (SSPs) (SSP1-2.6, SSP2-4.5, and SSP5-8.5), significant warming is projected across Vietnam, while precipitation projections remain uncertain, with most areas anticipated to experience slightly increased rainfall. SPEI results indicate that precipitation significantly influences drought conditions more than temperature, accounting for approximately 70% of the SPEI trend under SSP5-8.5, which consequently introduces substantial uncertainty in drought projections. Drought conditions under different global warming levels (GWLs) were investigated, showing that while drought may not occur more frequently at high GWLs, more extreme drought events are projected. Five models exhibiting the most pronounced increasing drought trends were further analyzed, revealing a eterioration of all drought characteristics, particularly in the Northwest, Northeast, and Central Highlands. Copula statistical analysis reveals that drought events with higher return periods tend to be more prolonged and severe in the future.