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Africa's food imports, 70 percent of which went to<sup>Nigeria. Many other cour. ies were affected to</sup> a lesser degree by commodity booms in the late<sup>1970s for cocoa, coffee, and phosphates, as well as</sup> the four other countries exporting oil. And growth<sup>in aid and borrowing of recycled OPEC revenues</sup> raised tae capacity to import of many African countries<sup>during the late 1970s. By contrast, the debt</sup> crisis in the 1980s reduced substantially the import<sup>capacity of many of these countries.</sup> The weather variable (lagged one year) is significant<sup>and has the expected sign: cereal yields</sup> below trend in year t-l are associated with increased<sup>food imports in year t. Despite the exclusion</sup> of food aid from the dependent variable, commercial<sup>food imports are responsive to shortfalls in</sup> domestic production caused by weather-related factors.<sup>Deteriorating weather, however, does not</sup> explain the secular rise in food imports since this<sup>variable is in terms of residuals, or deviations from</sup> trend, and the trend for most African countries,<sup>showed increasing yields for cereals over the period</sup> The trend variable is significant and has the expected sign.<sup>The value of the coefficient is small,</sup> however, suggesting a rise in food imports of only about<sup>1 percent per year. 23/ In addition, the</sup> significance of the variable in terms of its addition to<sup>the r-squared was very small as reported</sup> above. Nonetheless, a likely explanation for the significance<sup>of a slight trend is the decline in</sup> international rice and wheat prices over the period, which<sup>would be expected to raise imports.</sup> Wheat prices have falien in real terms by a third, and rice<sup>prices by half, between 1970 and 1986.</sup> Thus, in addition to the impact of exchange rate policies<sup>on the relative prices of domestic versus</sup> imported foods, border prices for imported foods have fallen<sup>over the period, encouraging additional</sup> substitution toward imports in consumption.

Overall, the regression results provide important evidence<sup>that Africa's food import growth has</sup> been, in part, demand driven rather than resulting from<sup>failed domestic production-although urban</sup> migration and trade and exchange restrictions are likely to have had<sup>an effect on supply as well.</sup> Demand has been influenced by go urnment policies, urbanization,<sup>and import capacity.</sup> Urbanization is the strongest explanatory factor. But government<sup>policies, to the extent they account</sup> for differences in rates of urban migration, under the<sup>strong relationship ateributed to urbanization.</sup> Evidence of that link is presented below.

# Policy and rural-urban migration

The link between policies and the rate of rural-urban<sup>migration has only been imprecisely</sup> identified thus far. Governments affect the rate of rural-urban<sup>migration through macroeconomic</sup> and pricing policies that alter the domestic, or rural-urban<sup>terms of trade. These include exchange</sup> rate policies and cheap food policies, both of which generally<sup>discriminate against the rural sector.</sup> In addition, govermnent programs such as the provision<sup>of schools, health service, and water</sup> supplies, may favor urban locations thereby encouraging<sup>migration. But determining the extent of</sup> these influences is problematic due to poor census data and<sup>the gradual nature of these demographic</sup> shifts. Anecdotal evidence provides some support to<sup>the importance of these policies on</sup> urbanization. For example, Zambia, which has had<sup>highly subsidized cheap food policies for more</sup> than 40 years, has the highest share of urban population<sup>in Sub-Saharan Africa.</sup> 2D Although not expressed precisely as a growth<sup>rate, the dependent variable is an index with</sup> an average value of 100 for the entire period. Thus<sup>a coefficient of 1 can be taken as</sup> approximating a 1 percent per year trend.