By Aaron Maasho

ADDIS ABABA Dec 8 (Reuters) - More than 10 million Ethiopians will need food aid in 2016, up from 8.2 million this year, due to the worst drought in decades, the charity Save the Children has said.

Although it has one of the highest growth rates in Africa, Ethiopia's economy still depends heavily on farming, which employs three quarters of the workforce in the nation of over 90 million people.

Caused by failed spring and summer rains and worsened by the El Nino weather phenomenon, the drought has led to food and water shortages.

About 8.2 million people are expected to have received aid this year, according to the government and the United Nations. The figure could spike to 15 million next year, the U.N. has warned.

John Graham, Ethiopia country director for Save the Children, said the charity estimated that 10.1 million Ethiopians would face critical food shortages in 2016.

More than half of those were children, of whom 400,000 would be at risk of developing severe acute malnutrition.

"The worst drought in Ethiopia for 50 years is happening right now," said Graham, adding that the estimated cost of the overall emergency response was $1.4 billion.

"We simply cannot sit back and wait until the situation has reached crisis point this time," he said in a statement.

Addis Ababa has so far spent 3 billion birr ($142.95 million) from its own coffers on relief efforts as only a portion of the aid money pledged by donors has been made available, Mitiku Kassa, head of Ethiopia's National Disaster Prevention and Preparedness Committee, said on Monday.

The El Nino weather pattern, marked by warming sea-surface temperatures in the Pacific Ocean, causes extremes such as scorching weather in some regions of the globe and heavy rains and flooding in others.

Meteorologists expect El Nino to peak between October and January and to be one of the strongest on record.

Last month, the United Nations Office for the Coordination of Humanitarian Affairs (UNOCHA) said floods caused by the weather anomaly were set to affect over 210,000 people and displace more than 100,000 people in Ethiopia.

Officials have dismissed concerns that the drought will have devastating consequences for the economy, saying growth was on course to meet forecasts of 10 percent in the 2015/16 fiscal year. ($1 = 20.9860 birr) (Editing by Drazen Jorgic and Estelle Shirbon)