Global Maize Shocks, Exchange Rates, and Domestic Consumer Prices in Ghana, Nigeria, Kenya, and South Africa

How a dollar maize shock does—or does not—become a local food-price shock once currency movements and domestic price structures intervene.

Published: 2026-06-28 | Kanari Intelligence

Executive Summary

Global maize prices matter for African inflation, but they do not pass cleanly or uniformly into domestic consumer prices. The literature is clear on the mechanism: the world-price shock arrives in US dollars, the exchange rate either amplifies or cushions it, and domestic market structure, trade policy, inventories, and food-basket weights determine how much of that shock reaches households.[1][2][3][4] In African settings, pass-through from international food prices to headline inflation is typically partial—often in the 5–15% range for aggregate inflation—while transmission into food-specific indices is usually materially larger.[1][3]

Drawing on monthly series for the global maize benchmark, national exchange rates, and domestic consumer prices, the clearest empirical result in this four-country set is not a broad, uniform maize-to-CPI corridor. It is a narrower pattern. Ghana shows the strongest evidence that exchange-rate movements help predict food-price movements: the cedi/USD rate Granger-causes Ghana’s food CPI at the 5% level over 1998–2026, while the direct global maize-to-food-CPI link is weak.[12][13] Kenya and Nigeria show no robust short-run predictive transmission from the global maize benchmark or the exchange rate into headline CPI over the available monthly samples. South Africa’s available exchange-rate overlap is too short for a reliable dynamic system estimate, so the South African result is best read from the literature and descriptive evidence rather than from a full multivariate monthly model.[4][5][9]

The practical conclusion is straightforward. The exchange rate is the more credible transmission corridor than the world maize price alone, but even that corridor is country-specific and depends heavily on the domestic price endpoint being measured. Ghana’s food CPI is the only food-specific monthly endpoint in this set, and it is precisely there that the exchange-rate link is clearest.[13] Nigeria, Kenya, and South Africa are assessed mainly through headline CPI, which is a broader and more diluted basket than food CPI and therefore a weaker detector of maize-price transmission.[1][7]

Key findings:

• African evidence points to only partial pass-through into headline inflation—typically about 5–15%—with stronger transmission into food-specific price indices than into aggregate CPI.[1][3]
• In Ghana, the monthly sample spans 337 observations from January 1998 to January 2026 for food CPI, and the exchange rate helps predict food CPI changes at the 5% level ($p=0.048$), while global maize prices do not.[12][13]
• In Ghana, the strongest simple association is between the exchange rate and food CPI, with peak cross-correlation around 0.98, versus only about 0.33 between global maize prices and food CPI.
• In Nigeria, the aligned monthly multivariate sample is 96 observations from 2016 to 2024, and monthly changes show near-zero correlations: 0.015 for maize vs NGN/USD, -0.095 for NGN/USD vs headline CPI, and -0.009 for maize vs headline CPI.[11][14][15]
• In Kenya, no national maize-price or food-specific CPI series was confirmed, so the analysis uses headline CPI only; Granger-causality p-values are 0.42 for maize → CPI and 0.10 for exchange rate → CPI, which is not strong enough to support a short-run transmission claim.[11]
• In South Africa, the overlapping monthly exchange-rate sample is only 26 observations, below the depth needed for a reliable VAR or impulse-response estimate, so no decision-grade dynamic pass-through estimate is reported.[4][5]
• The clearest transmission corridor in this set is Ghana’s exchange-rate-to-food-price channel, with the relevant horizon in the short run—within roughly 12 months—while the direct world-maize-to-domestic-price corridor is weak across the four-country evidence assembled here.[12][13]

1. Theoretical Framework

The literature gives a clear transmission map. A global maize shock starts as a US-dollar price movement. It then passes through the local currency via the exchange rate, and only then reaches domestic wholesale, retail, and consumer prices. In import-dependent African economies, that pass-through is significant but incomplete because governments intervene, traders hold inventories, transport and processing costs matter, and not every food item in the consumer basket is directly tied to imported grain.[1][2][3]

Two distinctions matter for interpretation.

First, world-price shocks and exchange-rate shocks are not the same shock. A 10% increase in the dollar maize price and a 10% depreciation of the local currency both raise the local-currency landed cost of maize, but they operate through different policy levers. Governments cannot control the Chicago or global benchmark price, but they can influence the exchange-rate environment, border policy, reserve management, and domestic competition conditions.[2][4]

Second, food CPI and headline CPI are not interchangeable endpoints. Food CPI is designed to capture food-price movements directly; headline CPI spreads the same shock across a much broader basket that includes housing, transport, clothing, and services. The literature therefore finds stronger pass-through into food-specific indices than into headline inflation.[1][3] That matters especially here: Ghana is the only country in this set for which a monthly food CPI series was available, while Nigeria, Kenya, and South Africa are assessed mainly through headline CPI.[13][14]

The literature also gives a time profile. Pass-through is usually not immediate. It tends to emerge over 3 to 12 months, depending on import dependence, inventory turnover, milling and retail concentration, and whether governments use tariffs, subsidies, or export controls to buffer consumers.[1][3][4] In southern Africa, maize is a politically sensitive staple, and policy efforts to stabilize local prices can delay or distort transmission rather than eliminate it.[5][6][8]

What this means: A country can be highly exposed to global maize shocks without showing a strong maize-to-headline-CPI relationship in the monthly data. The shock may be absorbed by the exchange rate, offset by policy, delayed in supply chains, or visible only in food-specific prices rather than in the full CPI basket.[1][3][4]