Chapter 2
Concepts of the climatic inventory

Temperature and water are the major climatic factors that govern distribution (both in space and time) of crops. In combination with solar radiation, these climatic factors condition the net photosynthesis and allow the plants to accumulate dry matter (and accomplish the successive development stages) according to the rates and patterns which are specific to cultivated plants.

While present knowledge does not allow full quantification of all agronomic consequences of climate in relation to crop adaptability and production, a number of important crop/climate relationships can be quantified in order to allow:

1. an assessment of the influence of climate on the spatial and temporal distribution of the crops¹;

2. the production that can be attained under conditions that are free from constraints.

The growing period has been used as a framework for the assessment of climatic resources. It is defined as the period in which temperature and moisture permit crop growth.

To take into account crop temperature requirements, prevailing temperature regimes have been inventoried by identification of thermal zones.

The inventory of climatic resources allows:

1. a differentiation of the country into reference thermal zones, reflecting the geographical and ‘seasonal’ distribution of the prevailing temperature regimes;

2. a differentiation of the country into reference length and pattern of growing period zones, reflecting the prevailing moisture regimes including the year-to-year variations;

3. a quantification of potential yields (crops, livestock and fuelwood) that can be attained under constraint-free conditions;

4. an assessment of various agro-climatic constraints to take into account yield losses likely to occur.

The synthesis of the moisture attributes of the inventory has been based on the analysis of historical rainfall records, and average monthly potential evapotranspiration calculated according to the Penman method.

The identification of thermal attributes of the inventory has been based on mean daily temperature, as related to other temperatures.

The methodology used for the compilation of the climatic resources inventory is described in the following sections, and involves the quantification of the growing period (and its variability) and the associated temperature regime.

¹ Crops of the assessment are: barley, maize, oat, pearl millet, rice, sorghum, wheat, cowpea, green gram, groundnut, phaseolus bean, pigeonpea, soybean, cassava, sweet potato, white potato, banana, oilpalm, sugarcane, pineapple, pyrethrum, sisal, tea, coffee, pasture and fuelwood.