Heavy rain in November 2025 Vietnam floods likely intensified by human-driven climate change

Contact Authors

• Davide Faranda, IPSL-CNRS, France  📨davide.faranda@lsce.ipsl.fr    🗣️English,French, Italian

• Valerio Lucarini, University of Leicester, UK 📨v.lucarini@leicester.ac.uk    🗣️English,, Italian

• Haosu Tang, University of Sheffield, UK  📨haosu.tang@sheffield.ac.uk 🗣️English

• Gianmarco Mengaldo, National University of Singapore,Singapore 📨mpegim@nus.edu.sg    🗣️English, Italian

Citation

•  Faranda, D., Lucarini, V., Tang, H., & Mengaldo, G. (2025). Heavy rain in November 2025 Vietnam floods likely intensified by human-driven climate change. ClimaMeter, Institut Pierre Simon Laplace, CNRS. https://doi.org/10.5281/zenodo.17777145

Press Summary

• Meteorological conditions similar to those causing the Vietnam floods are up to 9 mm/day (about +15%) wetter in the present than they have been in the past.

• This event was associated with exceptional meteorological conditions.

• We mostly ascribe the  heavier precipitation of November 2025 Vietnam floods to human driven climate change and natural climate variability likely played a modest role

Event Description

Between 16–22 November 2025, central Vietnam was struck by record-breaking rainfall, triggering widespread flooding, flash floods, and numerous landslides across the provinces from Quảng Trị to Đắk Lắk. According to national authorities and disaster-management agencies, as of late November the death toll reached 90people, with additional individuals reported missing, across the most affected provinces. Rainfall totals in some central provinces — especially in the south-central region — exceeded anything observed over the last 50 years. More than 200,000 houses were flooded and tens of thousands of hectares of crops destroyed. Roads, rail lines, and infrastructure were severely damaged or washed away; entire communities were cut off, and relief efforts had to rely on boats and helicopters for evacuations and aid delivery. The floods came after a season marked by multiple tropical depressions and storms (including the earlier impact of Typhoon Kalmaegi) in the region, compounding rainfall and saturation of soils. 

The meteorological conditions were characterized by weakly negative surface-pressure anomalies, with values down to about –1 hPa over central Vietnam, indicating a shallow but persistent low-pressure environment. Temperatures show scattered positive and negative anomalies reaching about 1 °C across large parts of the affected region. Precipitation locally exceeded 100 mm/day, with intense rainfall concentrated along the coast and over the interior highlands. Wind speeds during the event reached 40 km/h, with a pronounced easterly flow clearly enhancing moisture advection and contributing to sustained, heavy rainfall over central Vietnam.

Climate and Data Background for the Analysis

The IPCC AR6 report projects that in Southeast Asia, both mean monsoon precipitation and pluvial flooding are expected to increase, with greater intensity and frequency of heavy rainfall events as global warming progresses. These changes are attributed to the increased atmospheric moisture content under warming and amplified convective activity. Additionally, reduction of atmospheric aerosols associated with improvements in pollution management standards are also expected to contribute to the strengthening of the precipitation by reducing atmospheric stratification. Southeast Asia is identified in the AR6 WGI Summary for Policymakers as a region where heavy precipitation events will intensify and become more frequent.

Observational studies over the Indonesian Maritime Continent — including Bali — have documented upward trends in extreme rainfall indices, especially in response to intraseasonal variability like the Madden-Julian Oscillation (MJO). During active MJO phases, western and central Indonesia can experience up to 70–80% increases in extreme precipitation probability. Embedded in a climate system that is becoming wetter, climate variability contributes to the intensification of extreme events. The Indian Ocean Dipole (IOD) and El Nino–Southern Oscillation (ENSO) also modulate rainfall variability across Indonesia, including Bali, by influencing moisture advection and convection dynamics. Under anthropogenic warming, the Indo-Pacific warm pool has been expanding and warming, which strengthens moisture fluxes and amplifies extreme precipitation potential over maritime Southeast Asia.

Our analysis approach rests on looking for weather situations similar to those of the event of interest having been observed in the past. For this event we have low confidence in the robustness of our approach given the available climate data, as the event is very exceptional in the data record.

ClimaMeter Analysis 

We analyze here (see Methodology for more details) how events similar to the meteorological conditions leading to the September 2025 Bali floods have changed in the present (1987–2023) compared to what they would have looked like if they had occurred in the past (1950–1986) in the region [96°E–105°E, 4°N–9°N]. Surface-pressure changes between present and past are minimal over most of the affected region (near-zero anomalies), suggesting that the large-scale pressure forcing was not substantially different. Temperature changes show increases of up to +0.8 to +1.0 °C over parts of the region, indicating a warmer background state at the time of the 2025 event. Precipitation changes reveal a general increase in rainfall intensity: analogous weather situations are now up to 9 mm/day wetter than comparable events in the past — corresponding to roughly +15% in precipitation intensity under present-day conditions compared to the 1950–1986 baseline. Wind-speed changes show enhanced wind-speeds of up to +3–4 km/h over coastal or moisture-advection zones, favoring stronger moisture transport from the adjacent seas into the central Vietnamese highlands and coastal zones.

Similar past events do not show a clear seasonal shift. Changes in urban areas of  Hat Yai 'Songkhla, Trang are consistent with the regional trends: both precipitation and moisture-advection increased compared to similar past situations, increasing vulnerability to flooding given contemporary land use and development. These results suggest that meteorological conditions similar to those of the November 2025 floods in Vietnam are becoming more favorable for extreme precipitation events — consistent with expectations under continuing global warming.

Finally, we find that sources of natural climate variability, notably the El Nino—Southern Oscillation, may have only partly influenced the event. This means that the changes we see in the event compared to the past may be mostly due to human driven climate change.

Conclusion

Based on the above, we conclude that meteorological conditions leading to the November 2025 floods in Vietnam are up to 9 mm/day (up to 15% wetter) compared to similar past events. We interpret this as an event driven by exceptional meteorological conditions whose characteristics can mostly be ascribed to human driven climate change. The ongoing deforestation of some of the most affected regions has likely contributed to exacerbating the impacts of the exceptional rainfall.