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Increasingly erratic rainfall and unreliable cropping seasons in southern Africa, combined with high food prices, heighten vulnerability of rural people to food insecurity. To understand what actions are needed to expand adaptive capacity to climate change and its consequences for food security, it is useful to learn from existing agricultural practices in semi-arid areas that exploit positive opportunities of rainfall variability. To determine how residents attain food self-sufficiency based on rain-fed maize farming in a semi-arid region that receives an average annual precipitation of 400 mm, we carried out a detailed, interdisciplinary study of the agricultural system in Massingir, Mozambique from 2006 to 2010. We found that some people produced enough maize when rainfall conditions were favorable to sustain the staple food needs of a household for 2-3 years, buffering the negative effects of subsequent poor cropping seasons and avoiding seasonal hunger periods. To maximize production people employed a variety of practices including: planting after every rainfall event throughout the rainy season, up to six times in one season on as large an area as possible, as much as 18 ha per household, and employing labor/oxen exchange arrangements. We explored the role of these practices as key factors that determined total food production and variability among households. Although only 35% of planting events were successful, total seed sown represented only 8.5% of harvest over 15 years. Labor/oxen exchange arrangements allowed disadvantaged households to produce twice as much as without collaboration. Recent invasion of the large grain borer (Prostephanus truncatus), a devastating post-harvest storage insect pest, represents a major new threat to the sustainability of the agricultural system and to food security that could worsen with climate change. Our results suggest that policies aimed at reducing vulnerability to climate change could be improved through a deeper understanding of existing practices. (C) 2013 Published by Elsevier Ltd.