Variability in World Cereal Yields

Abstract

As world cereal yields rise there is increased concern with spatial and temporal variability in these yields and in the resulting food production. As mean yields increase absolute variability, both spatial and temporal, will also be expected to increase. However, if a common new technology is applied in agriculture, the producing areas might be expected to become relatively more alike. This, in turn, reduces the scope for compensation between areas with good and poor harvests and year to year variability is expected to increase. At a world scale, however, over the last 20 years spatial variability has increased relatively as well as absolutely. Technology is being applied unevenly and the cereal yield trends of different parts of the world are diverging. Temporal variability is increasing absolutely but not relatively-that is, it is increasing by only the amount to be expected to result from the increased mean yields. There are, however, great regional contrasts within this world picture with much of Africa, for example, facing declining yields compounded by rising relative variability, while over most of the rest of the world, especially in Europe and the United States, yields are rising and relative temporal variability is declining. The inequalities between those areas with an adequate food production and those without are increasing. There are important implications for the growth in world food trade and aid, their variability, and the need for national and international food security stocks.