Singapore on lookout for El Nino impact

The notoriously difficult-to-predict El Nino weather pattern that clouded Singapore in a haze crisis four years ago could be back in some form this year.

But this time, the Republic will be better prepared for it.

A new weather monitoring system was launched this year to better determine how El Nino - which usually brings hotter and drier weather to the region - could affect Singapore.

The system developed by the Meteorological Service Singapore (MSS) has indicated an "El Nino watch" state - one notch above "neutral" conditions.

This is because the system has detected a slight warming over the tropical Pacific Ocean - a sign of an El Nino brewing. If mature El Nino conditions are detected, usually from around June, the system will register its highest "El Nino" tier.

As El Nino events usually mature in the second half of the year, a better picture of whether the alert on the monitoring system will be upgraded should be able to be gleaned from later this month, said the MSS.

Mr Raizan Rahmat, head of the seasonal and subseasonal prediction section at MSS' Centre for Climate Research Singapore, told The Sunday Times: "The tiered warnings provide sufficient lead time that can better inform government agencies and user sectors across Singapore - such as national water agency PUB and the haze task force - so they can respond in a timely manner."

A spokesman for PUB added: "The MSS monitoring index gives an overview of the weather outlook in the next few months and updates on the possibility of an El Nino event.

"This provides PUB with early notice of possible dry spells and allows us to make preparations to ramp up production of Newater (reclaimed water) and desalinated water to continue to deliver an adequate and reliable water supply for all."

International climate centres such as the United States National Oceanic and Atmospheric Administration (NOAA) use various methods for monitoring and predicting El Nino events.

Previously, this caused difficulties in gauging the impact that El Nino could have on Singapore when the centres did not agree.

But MSS' new system has El Nino condition thresholds that are tuned more to Singapore's needs, said Mr Raizan.

By monitoring local and regional weather conditions, such as winds and clouds, the new system helps to contextualise what generic international predictions could mean for Singapore, said Mr Raizan.

For example, NOAA had in its June 3 forecast determined that "El Nino is present".

However, this is not the case for Singapore, given that El Nino conditions seem to be marginal, said Mr Raizan.

Morever, the aspect of El Nino that affects Singapore and the region the most - less rain clouds - has not yet been observed.

Developed over the past year at MSS' Centre for Climate Research Singapore, the new system is also able to separate changes in sea surface temperatures due to El Nino events, from the long-term warming trend due to climate change.

"Removing the background warming trend is needed to avoid overstating El Nino events, and understating La Nina events," said Mr Raizan.

El Nino and La Nina refer to the warm and cool phases of the El Nino-Southern Oscillation, a natural climate cycle that can significantly affect weather patterns around the world.

In South-east Asia, El Nino usually causes weather to be hotter and drier than usual. In 2015, a severe El Nino worsened the haze-belching forest fires in Indonesia and caused the region to suffer its worst haze crisis on record.

This climatic see-saw is tipped in the opposite direction during La Nina events. It causes more rain and raises the possibility of floods in South-east Asia.

MSS' new system provides warnings for both El Nino and La Nina events.

There are five warning tiers in all: neutral; two watch states that indicate developing El Nino or La Nina conditions; and two states to indicate El Nino and La Nina conditions.

The highest alerts are given when either El Nino or La Nina conditions are expected to last for at least four months.

Assistant Professor Winston Chow, a climate scientist from the National University of Singapore, said the lead time that the new system give to agencies to prepare for the effects of El Nino could be useful.

He said: "Water levels in natural streams and reservoirs could decline in the event of an El Nino-induced meteorological drought in the region.

"If the Johor River, Singapore's main water source in Malaysia, is affected, PUB could anticipate adjusting production from desalination and Newater to manage Singapore's water supply."

SEE INSIGHT

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How it affects ecosystems

For many Singaporeans, the term "El Nino" reminds them of an uncomfortable time in 2015 when a thick blanket of haze hung over the country.

Forest fires in Indonesia had been worsened by El Nino, associated with hotter and drier weather in South-east Asia. It resulted in the region's worst haze episode on record.

But it was not just humans who had a tough time coping. The hotter and drier weather also had an impact on Singapore's native ecosystems. The brunt of it, though, was borne by the ocean.

The National Parks Board (NParks), custodian of Singapore's native biodiversity, estimates that about 15 per cent to 20 per cent of the coral here died in the aftermath of the 2015 El Nino.

The El Nino event caused sea surface temperatures to go up. It resulted in heat stress accumulating to the extent that it caused the coral to bleach for around three months, said Dr Karenne Tun, director for the coastal and marine branch at NParks' National Biodiversity Centre.

Bleaching occurs when warming seas cause hard coral to expel algae that provide them with nutrition, turning them white. Although the situation led to bleaching across all coral reefs in Singapore, the bleaching intensity and severity varied between species and among individuals and sites, with recovery from bleaching estimated at over 80 per cent by the end of 2016, she added.

The slight change in temperature may not seem like much on the thermostat, but it could mean life or death for reef-building hard coral. Prolonged bleaching could result in the coral dying.

The coral in Singapore are susceptible to slight changes in ocean temperature because normal water temperatures are already close to their bleaching threshold.

For instance, during the warmest months of May and June, the monthly mean sea surface temperatures in coastal waters are above 30 deg C, close to the upper temperature tolerance for coral, said Dr Tun.

She added: "Any slight increase in sea surface temperatures can increase the heat stress which, if sustained for longer periods of time, can result in bleaching."

For a coral reef, full recovery from a severe bleaching event can take more than five years, depending on the severity and other conditions, said Dr Tun. Research is ongoing to understand the local impact and opportunities resulting from mass bleaching events, she added.

On land, Singapore's forests appeared to be more resilient to the impact of the 2015 El Nino, which brought with it about 20 per cent less rainfall compared with the average for the February to May period.

Dr Thereis Choo, director for the terrestrial division at NParks' National Biodiversity Centre, said this is likely because even during El Nino years, conditions are still within tolerable limits for the trees.

She said: "While there is a tendency for conditions to be drier than usual during El Nino years, the absolute rainfall is still relatively high and within the variation in rainfall seen in Singapore in all years."

Observations by the Meteorological Service Singapore (MSS) indicate as much. Mr Raizan Rahmat, head of the seasonal and subseasonal prediction section at MSS' Centre for Climate Research Singapore, said rainfall during El Nino years is usually near or below average.

"However, during El Nino neutral years, rainfall could be above, near and below average," he said.

However, with climate change increasing the likelihood of more weather extremes such as drought, NParks is taking steps to safeguard Singapore's native vegetation.

For example, research is ongoing to determine how the hydrology of the Nee Soon Swamp Forest - Singapore's last remaining primary freshwater swamp forest in the Central Catchment Nature Reserve - would be affected by drought.

NParks is also planting more drought-tolerant native species all over Singapore, so that watering can be done more prudently.

Examples of these trees include the critically endangered seashore mempari and the Illawarra flame tree.