The study was carried by the University of Cape Town, which analysed climate impact on agriculture in Angola, Lesotho, Malawi, Mozambique, Rwanda, Uganda, Zambia and Zimbabwe.
It projected a temperature rise of around two degrees Celsius (3.8 degrees Fahrenheit) by 2069, and up to 2.6C in some places.
"The eight countries analysed are very different, landlocked, coastal, mountainous or semi-arid, but the conclusions are repeated and grim," said IFAD, a specialised UN agency.
"Rainfall will be scarcer but also more erratic, with flash floods threatening crops and soil stability," it said.
Corn, also called maize, requires a lot of water to grow, which will add to pressure on farmers to switch to strains that mature earlier, or to switch to more resilient crops such as cassava, peanuts, beans, sorghum and millet.
But moving to different crops is easier said than done, as there can be strong market preferences, IFAD said.
Farmers also face many financial and technical hurdles as they contemplate a switch, from advice on seeds and the acquisition of new tools to the processing and storage of crops to prevent spoilage.
Click here to see more...