The UN has appealed for more than $7bn for the three countries, but prior to Wednesday's pledging conference Somalia was just 25% funded, Ethiopia 22% and Kenya just 21%.
The United Nations describes the Horn of Africa as the epicentre of one of the world's worst climate emergencies.
"People in the Horn of Africa are paying an unconscionable price for a climate crisis they did nothing to cause," Guterres told the pledging event in New York on Wednesday.
"Crisis atop of crisis is threatening the lives and livelihoods of millions across the Horn of Africa: The longest drought on record. Mass displacement after years of conflict and insecurity. Skyrocketing food prices," he said.
According to the World Health Organization and Unicef, some 40,000 died during a drought in Somalia last year; half were children under the age of five, Guterres said.
The United States made the top pledge - an additional $524m, taking its total for fiscal 2023 to some $1.4bn. The European Commission pledged $185m, Germany $163m, Britain $120m and the Netherlands $92m.
"This is a global problem that requires all of us," US Ambassador to the United Nations Linda Thomas-Greenfield told the pledging event.
"We must adapt to the impacts of climate change and build more sustainable, equitable, and resilient food systems around the world. And we must support humanitarian workers and NGOs that dedicate their lives to saving lives," she said.
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