He will also head the Office for the Coordination of Humanitarian Affairs (OCHA) in his new role.
The UN agency said from the beginning of the year, heavy rains have caused severe flooding and landslides across Burundi.
The displaced were seeking refuge in the towns of Kobo and Sekota in the Amhara region.
More than 100 casualties were recorded in the suicide bombing.
Sudan often witnesses floods caused by heavy rains from June to October.
Somalia has an estimated 2.9 million internally displaced persons, one of the most in a single country.
