AbstractMeteorological definitions of drought are deemed to reveal little of the effects of water deficiencies upon the inhabitants of arid regions. An agricultural definition of drought is obtained using a water‐balance model of the moisture available to millet (Pennisetum typhoides).The model accepts inputs of rainfall, potential evapotranspiration, and crop development for 5‐day periods. Values for field capacity, wilting point, bulk density, crop coefficients, and rooting depth are obtained, and changes in soil moisture, actual evapotranspiration, and drainage are computed. The resulting seasonal millet moisture deficits are mapped for ‘millet drought’ in Niger from 1967 to 1978. These maps indicate that for traditional areas of millet cultivation, ‘millet drought’ was a rare event during the 1970s, but was common and widespread in the more northerly, marginal lands.