East Africa's five nations - Kenya, Rwanda, Tanzania, Uganda and Burundi - have increasingly experienced extreme weather events in recent years.
Climate change will force tens of millions of East Africans to abandon their homes within the next three decades, even if schemes to reduce its impact on the region are rolled out, the World Bank said.
People affected will include drought-stricken farmers seeking new arable land or different work in urban areas, and others driven out by the need to find clean water, the Bank said.
Apart from a worsening drought in a region heavily reliant on agriculture, there was extensive flooding in 2020, while a locust infestation of historic proportions that began in 2019 continues to wreak havoc.
"Without broad, urgent action... as many as 38.5 million people could be internally displaced as a consequence of climate change by 2050," said Hafez Ghanem, World Bank vice president for the region.
Steps to reduce greenhouse gas emissions and fund climate change and adaptation schemes could cut the projected number of displacements, but only by 30%, the bank's report said.
"Climate action is still under-funded," said Keith Hansen, World Bank's country director for Kenya.
Rich nations promised in 2009 to deliver $100 billion a year for five years from 2020 to poorer countries to help them tackle the impact of global warming. But that funding programme is set to be delayed by three years.