Chapter 6
Thermal zones

To identify thermal zones, temperature criteria corresponding to the requirements of crops, pasture and fuelwood were taken into account (Technical Annexes 3, 4, 5 and 6)¹

To cater for differences in temperature requirements of crops in the compilation of the country inventory, commensurate with the scale of the assessment (1: 1 million) thermal regimes have been defined based on 2.5 °C intervals. A thermal difference of 2.5 °C corresponds to an altitudinal change of 385 m, thus allowing a sufficiently fine matching of crop thermal requirements to prevailing thermal conditions as inventoried²

For Kenya nine reference thermal zones have been recognized as shown below.

¹ Field crops, pasture and fodder grasses and legumes, and fuelwood tree species have been classified into temperature-photosynthesis adaptability groups. Four temperature adaptability groups are recognized for field crops, four for pasture and fodder grasses and legumes and two for fuelwood species (each with three productivity classes).

² Data from meteorological stations above 150 m altitude conform closely to the following relationship between average daily temperature in degree Celsius (T) and altitude in metres (A): T = 30.2 - 6.496 ( A / 1000 ). Temperature seasonality effects of latitude are minor due to the equatorial position of Kenya.