Permaculture Designers Manual
CHAPTER 5 – CLIMATIC FACTORS IN PERMACULTURE
Section 5.2 –
The classification of Broad Climatic Zones in Permaculture
Most global climatic classifications are based on precipitation-radiation interactions as formulated by Vladimir Koppen (1918) and subsequently modified and updated by authors such as Trewartha (1954).
Figure 5.1 is from the latter reference. More closely-defined plant lists can be given by reference to the “Life Zone” matrix developed by Holdridge (Figure 5.2), which has enabled James Duke and others to annotate plant lists with concise climatic keys.
Figure 5.1 Koppen Climate Classifications
Many plant compendia attach “zones of hardiness” to plant listings, commonly used in the USA. As given in Hortus Third, the zones are in Table 5.1.
Measures or cut-off points are usually chosen that approximate the limiting boundaries for life forms, and are mainly good approximations of lethal or optimum ranges.
The main qualifying factors on the broad classification of climatic factors are:
Special mountain conditions;
The modifying effects of coasts (and the extremes of continental interiors);
Local energy transfer by winds and oceanic currents; and
Long-term cyclic factors.
Some problems in this area are:
1. Instruments for accurate measurement are expensive, and often specific to a narrow range of the total spectrum of effects.
2. Averages in such areas as precipitation and radiation often refer only to one part of the total spectrum. We have few long-term records of fog precipitation, dew, long-wave radiation, ultraviolet incidence, or gaseous atmospheric composition.
3. We are aware that rain, sun, and wind interact in a dynamic and continuous fashion so that averages mean little to a plant or animal subject to the normally changeable effects that may cover wide ranges of interactive measures.
In this Module, we are concerned only with the very broad climatic zones (design specifics for each climatic zone are given in later chapters).
These have been grouped as follows:
TROPICAL: no month under 18°C (64•f) mean temperature, and
SUBTROPICAL: coolest months above o•c (32°F) but below 18°C (64°F) mean. In effect, frost-free areas.
TEMPERATE: coldest months below OOC (32°F), warmest above I0°C (50°F) mean temperature, to POLAR: warmest month below 10•c (50°F) or in perpetual frost (8°C or less) mean.
ARID: mean rainfall SO em (19.5 inches) or less to DESERT: mean rainfall 25 cm (10 inches) or less. Includes sub-humid, or any area where evaporation exceeds precipitation