The study by the independent policy institute Chatham House found governments and humanitarian agencies were missing opportunities for early action, and estimated 2 million people have died in drought-related emergencies since 1970.
The report analyzed such emergencies globally, but focused on the Horn of Africa and the Sahel region south of the Sahara, citing Somalia -- where no actions were taken despite 11 months of drought warnings.
"The regions are quite unique in a way because you have these droughts, where there are normally successive failed rains; then you have a process whereby you have subsequent harvest failures then people adopt coping strategies," report author Rob Bailey told the BBC. "They start selling off assets, running down food reserves, taking on credit -- they get themselves into an increasingly desperate situation."
Those coping strategies became exhausted, triggering a famine, he said.
"But the whole process can take 11 months from start to finish, and that is why there is an opportunity to intervene early," he said. "Yet despite this very significant opportunity and despite analysis showing that when you do intervene early it costs less and you save more lives, it does not happen."
Perceived political risks by governments often are a cause of delays in relief efforts, he said.
"They see political risks in funding these sorts of things because budgets are tight and public support for aid spending is less than it used to be, so it is seen as a particularly risky endeavor at the moment."