El Nino floods could displace more than 100,000 people in Ethiopia, where more than 8 million people are facing a food crisis, the United Nations says.
Failed rains during both the spring and summer have created food and water shortages in the Horn of Africa nation.
The government and aid agencies say Ethiopia needs $US600 million to cope with the crisis.
Ethiopia, brought to its knees by famine in 1984, which killed hundreds of thousands of people, now boasts one of the world's fastest growing economies and is far better able to cope with a new crisis, experts say.
The government said agriculture had a smaller role and double-digit growth forecasts would not be knocked off track this time.
"El Nino has a dual impact on Ethiopia, causing drought in the north, central and eastern parts of the country, and flooding in south and south eastern areas," the Office for the Coordination of Humanitarian Affairs (UNOCHA) said in a report.
"At least 210,600 people are expected to be affected by flooding and at least 105,300 people risk displacement," it said.
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.
Aid agencies have said the number of people needing support in Ethiopia could rise to 15 million by early 2016, with 350,000 children expected to require treatment for acute malnutrition by the end of 2015.
More than 600,000 tons of wheat purchased by the Ethiopian government is expected to arrive in neighbouring Djibouti this week, the United Nations said.
Addis Ababa has so far allocated more than 6 million birr ($395,745) to tackle the effects, it added.
Abraham Tekeste, deputy head of the National Planning Commission, said on Monday that Ethiopia's economy was on course to meet growth forecasts of 10 per cent in the 2015-16.
"The structure of the economy has changed. It has become diversified now," he said, adding agriculture now accounted for 38 per cent of national income versus 60 per cent only five years ago.
"The economy has become resilient to shocks now."
However, consultancy group Teneo Intelligence said in a note last week that growth projections of 10 per cent in 2015-16 could be revised down if there is a sustained drought.