How, why global forecasters got La Nina prediction wrong
It’s October and the El Nino Southern Oscillation (ENSO) conditions are still continuing. There’s no sign of a positive IOD effect; IOD remains neutral.
Most global agencies got the La Nina forecast wrong this year, India Meteorological Department said on Tuesday.
US’s National Oceanic and Atmospheric Administration (NOAA) issued a La Nina watch in May, indicating that La Nina conditions were expected soon.
An IMD forecast in May confirmed that La Nina conditions would be established during the second half of the monsoon, which would also see the emergence of a positive Indian Ocean Dipole (IOD) condition.
It’s October and the El Nino Southern Oscillation (ENSO) conditions are still continuing. There’s no sign of a positive IOD effect; IOD remains neutral. And the delay in the establishment of La Nina may lengthen the warm streak seen globally since last October , experts said.
ENSO is one of the most important climate phenomena on Earth due to its ability to change the global atmospheric circulation, which in turn, influences temperature and precipitation across the globe, according to NOAA.
El Nino refers to a warming of the ocean surface, or above-average sea surface temperatures (SST), in the central and eastern tropical Pacific Ocean while La Nina refers to the periodic cooling of ocean surface temperatures in the central and east-central equatorial Pacific that occurs every 3 to 5 years or so.
These phenomenon are a part of natural climate variability. In India, an El Nino is associated with harsher summer and weaker monsoon. La Nina, meanwhile, is associated with strong monsoon and above average rains and colder winters.
IOD is the difference between the temperature of the ocean in two parts — in the Arabian Sea on the west and the Bay of Bengal in the east. A neutral IOD doesn’t affect the monsoon, but a negative one is bad news for the monsoon.
“None of the models globally go the t La Nina forecast right. But circulation features resembled La Nina which helped the monsoon. It needs to be researched as to why models gave those signals,” said M Mohapatra, director general, IMD.
Experts believe the climate crisis may be responsible for the anomaly.
“Probably, the most important reason may be global warming. The past year saw very hot months and ocean temperatures were up. Global warming may have lead to the asymmetric evolution of El Nino and La Niña. The models do not factor in these effects of global warming,” said M Rajeevan, former secretary, ministry of earth sciences and climate scientist.
“The expected La Nina event was a weak/ moderate . Normally models have poor skill in predicting these weaker events. Models do well on stronger events because the signal is much stronger,” Rajeevan added.
Whatever the reason, the slow transition has led to a continued warm streak .
“ The expected transition from ENSO-Neutral to La Niña continues to proceed slowly, as if the whole Pacific is stuck in a summer daze, moving as slow as molasses,” NOAA said in its blog on August 8.
Surprisingly, unlike other climate phenomena which can be difficult to predict even two weeks prior, the phase of ENSO can be predicted many months in advance, giving communities worldwide vital time to prepare.
NOAA also admitted to the disruptive effects of global ocean temperatures.
“The burning-hot, must-be-suffering-from-heat-exhaustion-at-this-point elephant in the room continues to be the hot streak Earth has been going through for more than a year (as well as the longer warming trend associated with human-caused climate change). Global ocean temperatures have been record breaking every month for well over a year. And just as we noted some uncertainty on how this would affect the 2023-24 El Niño (RIP), the same goes for any developing La Niña,” NOAA added.
As per Climate Reanalyzer of the University of Maine, temperatures have reduced marginally compared to 2023 levels, but remain extremely high. On September 26, average global temperature remained 1.2 degrees C higher than 1979-2000 average. Sea Surface Temperatures globally dropped marginally in August and September but reached a record high again on September 26.
India recorded an exceptionally warm monsoon season. It was the warmest June for northwest India since record keeping began in 1901. India recorded its second warmest July since 1901 in terms of mean temperatures and the warmest July by night time temperatures. It was also the warmest August for the country in terms of night time or minimum temperatures.
“Though we recorded above normal rain at 108% of long period average, it was also a warm monsoon. It’s possible that ENSO neutral conditions meant warm days continued. But there is a trend of warm monsoon months for several years now. It rains heavily on few days and moderate rain days have declined completely. So though the average rain quantum is above normal, on dry or light rain days heat increases leading to warm monsoon months,” added Mohapatra.
IMD forecast on Tuesday that the probability forecast indicates a higher chance of development of La Niña conditions in the post monsoon season (October to December). NOAA has said La Niña is favoured to emerge in September-November (71% chance) and is expected to persist through January-March 2025.
The impact of emerging La Nina will not be felt immediately. There is likely to be above normal rainfall during October over most parts of the country at 115% of the long period average, the India Meterological Department has forecast. Day and night temperatures are also likely to be above normal over the country during October, IMD has warned.