San José, Costa Rica, since 1956

El Niño Behind This Year’s Rain Drop-off

The typical Central Valley rainy season scene of black umbrellas bobbing up and down along Avenida Central has been absent lately.

Sunshine has been the norm in this abnormal season, especially since July. But scientists at the National Meteorological Institute (INM) said Tuesday that this year’s extended dry season will come to an end. Rainfall across the country is expected to return to normal this week, and umbrellas will be dancing in the streets once again.

While a short break from the rainy season is typical in the early weeks of July, meteorologists said that the presence of the meteorological phenomenon El Niño in Costa Rica this year has prolonged the canículas – or dog days – and forced an extended dry period in the Central Valley and along the Pacific coast.

These areas recorded less than average amounts of rain for the month of July, with rainfall approximately 50 percent below the 12-year average from 1996 to 2008.

El Niño has caused high pressure systems in the Atlantic, which, in turn, has caused strong east-to-west winds, unusual for this time of year. Bringing moisture off the ocean, these winds drop excessive rainfall on the country’s Atlantic slope, but by the time they reach the Central Valley they have lost their moisture, and carry dry air through the valley and out to the Pacific.

“There are some pressure systems in the Atlantic that have been particularly strong,” said Eladio Solano, a meteorologist with the INM. “El Niño has forced some oscillations along the Caribbean that favor rain along the coast, but not in the Central Valley or along the Pacific.”

Between the months of January and July, the airport at the Caribbean port city of Limón received more than 3,100 millimeters of rain. The average for the area is just over 2,000 mm for the same time period.

Meanwhile, Paquera, in the province of Puntarenas along the Pacific coast, an area that receives an average of 947 mm of rain between January and July, has received less than 500 mm so far this year.

El Niño presents itself every three to five years when the Pacific Ocean is warmer than usual, and the phenomenon can last from six to 18 months. The last time El Niño was present in Costa Rica was from August 2006 to February 2007.

The systems that prolong El Niño remain a matter of conjecture, but Costa Rican meteorologists predict that this year’s effects will last until the beginning of next year, which could mean an earlier end to this year’s rainy season.

The INM predicts that the rainy season could begin to decline 15 days to one month earlier than its usual mid-November finale. Solano noted that the institute expects less than average rainfall during the month of October.

What Does the Dry Spell Mean?

Among the driest areas of the country this year is the northwest province of Guanacaste and, especially, that region’s NicoyaPeninsula. The peninsula receives an average rainfall of 256 mm for the month of July, but this year it has received only 106 mm.

Oscar Gerardo Vásquez, regional director for the Ministry of Agriculture and Livestock for the country’s northwest sector, said rice farmers have noticed dry, brown tops on their plants since the end of July.

Vásquez said that it is too soon to tell if the lack of water will result in a significant crop loss come harvest season, but he said a July study revealed that if the weather continues to be as dry as it has been, farmers in the Nicoya area could see a 30 percent drop in their year-end yields.

Solano said that the following months will bring more rain than did July to the parched area, but he warned that the anticipated abrupt end to the rainy season will “absolutely affect the agricultural sector in Guanacaste.”

Vásquez said he is working with farmers to prepare irrigation systems in the event their plants continue to deteriorate.

As for energy, the Costa Rican Electricity Institute (ICE) has reported that the reservoirs of the nation’s hydroelectric plants, which are responsible for up to 80 percent of the country’s energy, had not been severely depleted by last month’s water shortage.

Both LakeArenal, in the country’s northern region and Cachí, east of Cartago, have received sufficient rainfall to calm any major blackout concerns, according to ICE and INM. Both of these areas receive rainfall from the Atlantic.

“It has been rainy enough in these regions and, up to the moment, there is no problem,” Solano said. “If there is good management of the hydro sources, they can continue to rely on it. But come October, if they haven’t used it rationally, they won’t be able to maintain (production).”


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