Above average rainfall likely
The Vanuatu Meteorology and Geohazards Department is predicting above average rainfall in coming months with La Niña climate conditions likely to form.
The department says climate model outlooks have shown an increased likelihood of La Niña forming in 2021; and is warning of increased risks of flash flooding and landslides.
In response, the department has raised its to El Niño Southern Oscillation (ENSO) Outlook status to ‘La Niña WATCH’ for the coming months.
This means that while ENSO currently remains neutral, the chance of La Niña forming has increased to around 50 per cent.
Most oceanic and atmospheric indicators of ENSO remain within the ENSO-neutral range.
However, sea surface temperatures in the central tropical Pacific Ocean have cooled over the past two months, supported by cooler than average waters beneath the surface.
Climate models predict the continuation of this cooling trend in coming months, with three of the seven models surveyed by the department meeting La Niña criteria, and two briefly reaching La Niña thresholds.
The department says all rainfall sites throughout Vanuatu have recorded below normal to normal rainfall during the last three months.
But, climate models are showing above normal wet season rainfall is likely for Vanuatu from October to December 2021, if the ENSO status continues to develop towards La Niña conditions.
The department’s Climate Service Manager, Allan Rarai, says La Niña-like conditions would bring above normal rainfall which may cause flash flooding, flooding of low-lying areas and landslides.
Vanuatu also experienced La Niña conditions in 2020 and Mr Rarai says that caused wet season flooding and landslides in some areas with people having to relocate from settlements on river banks.
Mr Rarai says during the wet season people should save and store water for the dry season.
The department says its next advisory will clarify whether the likelihood of a La Niña event this occurring this year has increased or decreased.
Meanwhile, the department is advising communities to take “appropriate preparatory actions, consult relevant authorities for specific information and stay up-to-date with the latest departmental information”.
Vanuatu’s wet season is from November to April and its dry season from May to October.
La Niña and El Niño are ocean-atmosphere phenomena that are opposite phases of the ENSO cycle, which describes the fluctuations in temperature between the ocean and atmosphere in the tropical Eastern Central Pacific Ocean.
La Niña, which is a Spanish term for ‘little girl’ involves ‘cooling of the sea surface’, while El Niño or ‘little boy’ involves the ‘warming of the sea surface’.
These changes from normal sea surface temperatures can have large-scale impacts on ocean processes and global weather and climate.
During a period of La Niña, the sea surface temperature can be lower than normal by 3 to 5 °C.