This connects again to Devilstower's Africa diary:  rail, port and road infrastructure in much of the Third World is post-colonial and engineered strictly for efficiency in removing resources from the country, not for transporting food around rapidly when needed to balance out supplies in drought or flood years.  One of the reasons for the near-elimination of famine (which is a different thing from delocalised hunger due to poverty) in Europe and the US is the ability to shift food stocks around very rapidly (not that you'd know it from the inept response to Katrina).  Canals and railroads made a huge difference in governments' ability to shift surpluses to areas where there was a food deficit...  anyway, the unidirectional extractive nature of infrastructure in much of the Third World makes this more difficult and expensive (having to use airlifts, etc)...

The difference between theory and practise in practise ...