Living organisms require heat, light
and water in varying amounts. Their distribution, in space and time, is governed
by these climatic elements. These parameters condition rates of net photosynthesis
allowing plants to accumulate dry matter and to accomplish the successive plant
development stages. Data on climatic requirements of crop growth, development
and yield formation are the basis for the compilation of the AEZ
climatic inventory. Prevailing temperatures determine crop performance when
moisture conditions are met. Similarly, when temperature requirements are met,
the growth of a crop is dependent on how well its growth cycle fits within the
period when water is available. The latter has led to the concept of length
of growing period (LGP). It
provides for an environmental characterization particularly relevant to agricultural
assessments. The length of growing period is defined as the number of days when
water availability and prevailing temperatures permit crop growth.