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 75% of the SPEI trend under SSP5-8.5. Drought conditions under different global warming levels (GWLs) were investigated, showing that drought characteristics—except for intensity—are projected to become milder in the future, with the central coastal area exhibiting the most pronounced and statistically significant changes. Six models exhibiting the most pronounced increasing drought trends were further analyzed, revealing that drought severity and intensity could worsen under the worst-case scenarios, particularly in northern Vietnam and the Central Highlands. Copula analysis reveals that drought events with higher return periods tend to be more prolonged and severe in the future. Our findings provide critical scientific evidence to inform national adaptation strategies and regional water resource planning under future climate change.