El Niño update: Central Panama's driest three-year span

STRI/DICYT Few weather phenomena dominate Panama’s weather for more than a few days or weeks. The exception is the El Niño/La Niña cycle, also known as the El Niño Southern Oscillation (ENSO). Since May, 2015, Panama has been strongly influenced by one of the greatest El Niño events ever recorded, contributing to one of the country's most severe recorded droughts.

The drought is affecting not only many aspects of Panamanian society but also Panama’s oceans and terrestrial ecosystems. Severe climatic events such as this present unique opportunities for scientists to study how nature responds. The coming months of Panama's hot, dry season should lead to findings pertinent to how tropical societies and ecosystems can deal with climate change and drought.

Underpinning this research is the meteorological, hydrological and oceanographic data provided by STRI's Physical Monitoring Program, which maintains monitoring equipment at STRI's primary research facilities. In addition, data from the Panama Canal Authority (ACP) and Empresa de Transmisión Eléctrica S.A. (ETESA) are available to provide data for locations not directly monitored by STRI. The following are highlights from last year.

Central Panama is currently suffering the most severe three-year drought in its history. 2013 to 2015 constitute the driest three consecutive years recorded on Barro Colorado Island, in the middle of the Panama Canal, where data has been collected for almost a century. 2015 was the second-driest year every recorded on BCI and in the Panama Canal watershed. The severe drought extends from the southern tip of the Azuero Peninsula to at least the eastern borders of the provinces of Panamá and Colón. Data from Tonosí, Los Santos, Divisa, Antón and Panamá all indicate one of the driest years recorded. On the other hand, the Bocas airport on Isla Colon indicates that this has been the eighth-wettest year recorded.

-Air and ocean temperatures have been well above average since at least May. In particular, ocean temperatures in the Pacific were up to 5 degrees Celsius above normal for several months – only recently have they started to cool down. Air temperatures have been 1-2 C above average, peaking in December at almost 2.5 C higher than normal.

Abnormal Niño

El Niño events occur every three-seven years but major events are less frequent – every eight to 17 years. ENSO events do not always affect Panama, but when they do the effects usually begin in July. This year was different.

On BCI the rainy season started at the end of May, two weeks later than normal. There were about three weeks of typical rainy season weather and then something almost never seen before happened – the rains stopped, giving the appearance that the dry season had returned.

From mid-June to mid-August rains were less than half of normal. Water levels in Lake Gatun were more that half a meter below the lowest levels ever seen that time of year. The small Lutz stream on BCI, which has been monitored since 1972, went dry during the rainy season for the first time ever. Corals began to bleach in the Pacific.

Then Central Panama got a break. Against all odds and predictions, the rains returned near the end of August and were average or above average until October. Lake Gatun, the main reservoir of the Panama Canal, recovered more than a meter. But by the beginning of November the rains began to diminish, all but disappearing by the end of the month. According to the ACP, this year’s dry season had the fourth earliest start on record.

The rainy season gave Panama one parting gift, however. A major storm added two meters to the level of Lake Alajuela, a secondary reservoir for the Panama Canal and a major source of potable water for Panama City. The lake ended the dry season below average but above levels seen in previous major El Niño events. For many people in Panama's most populous areas, this single storm may be the difference between running out of water or not near the end of April.

What’s in store this year?

Having already shown itself capable of big surprises, it is difficult to know how this El Niño is going to play out. Past major El Niño events resulted in very severe dry season that last until mid-May. This is the current prediction by the ACP. These events were then followed by average to slightly above rainfall during the next six months. In three out of four cases, the following years have been very wet. Temperatures, both in the ocean and in the air, should continue to be above average for the next four-five months and then return to normal.