Permaculture Designers Manual
CHAPTER 5 – CLIMATIC FACTORS IN PERMACULTURE
Section 5.1 –
Introduction to Chapter 5 in Permaculture Designers Manual
However, long-term prediction of the weather, over a scale of more than about 10 days is a thankless task.
This is because the dynamics of the atmosphere form a system whose behavior is usually chaotic.
The surface of the earth absorbs heat and so heats the atmosphere from below and this warm air rises.
Heat is lost from the upper atmosphere and this cooled air falls.
A roughly hexagonal cellular array of vortices forms, with the ascending warm air feeding the descending cool air.
(Arun Holden, New Scientist, 25 Apr ’85.)
The glass is falling hour by hour
The glass will fall forever
But if you break the bloody glass
You won’t hold up the weather.
Climatic factors have their most profound effect on the selection of species and technology for site, and are thus the main determinant of the plant, animal, and structural assemblies we can use.
There is all intimate interaction between site and local climatic factors, in that slope, valley configuration, proximity to coasts, and altitude all affect the operation of the weather.
Such factors as fire and wind effects are site and weather related. It is the local climate that inevitably decides our sector strategies.
Although we will be discussing the individual weather factors that define climate, all these factors interact in a complex and continuously variable fashion. Interactions are made even more unpredictable by:
Longer-term trends triggered by the relative interaction of the orbits of earth, sun and moon;
Changes included in the gaseous composition of the earth’s atmosphere due to volcanism, industrial pollution, and the activities of agriculture and forestry;
Extraterrestrial (actors such as meteors. the perturbations in high-level atmospheric jet streams, the oceanic circulation, by fluctuations in the earth’s magnetic field, and by solar flares.
There is a general consensus that world climatic variation (the occurrence of extremes) is increasing, so that we can expect to experience successively more floods, droughts, periods of temperature extremes and longer or very intense periods of wind.
We have separated climatic studies from that of earth surface conditions, and there are climatologists who know little of the effects of forests, industrial pollutants, agriculture, and albedo (albedo is the ratio of light reflected to that received) on the global climate.
There is no longer any doubt that our own actions locally greatly affect global and local climate and that we may be taking unwarranted and lethal risks in further polluting the atmosphere.
Because climatic prediction may forever remain an inexact science, we should always allow for variability when designing a site.
A basic strategy Is to spread the risk of crop failure by a mixture of crop species, varieties, and strategies.
This fail-safe system of mixed cropping is basic to regional self-reliance, and departure from such buffering diversity brings the feast-or-famine regime that currently affects world markets.
In house design, the interactions of thermal mass (heat storage) and insulation (buffering for temperature extremes) plus sensible siting permit us to design efficient and safe housing over broad climatic ranges.
Strategies such as water storage and windbreak modify extreme effects. Many plant and animal species show very wide climatic tolerances, and local cultivars are developed for almost all important food plants.
The variety of food grown in home gardens varies only slightly over a great many situations.
As designers, we are as interested in extremes as in means (averages). Such measures as “average rainfall” have very little relevance to specific sites.
Of more value are data on seasonal fluctuation, dependability, intensity and the limits of recorded ranges of any one factor. This will decide the practical limits that need to be included in a design.
People who are called on to design or instruct over wide climatic ranges would do well to read in more general treatments such as Eyre (1971) and James (1941), or in modern bio-geographical texts. These treatments deal with world vegetation patterns and climatic factors.
Total site factors related to land configuration will impose specific limits to any design; soil data will also be specific to site.
There is, therefore, no substitute in any one design for local observation, anecdotes, detailed maps of local factors, lists of locally successful plant and animal species and analysis of local soils.
It is obligatory for any designer to study the regional long-term human and agricultural adaptations to climate.
Above all, we should avoid introducing temperate (European) techniques and species to tropical and arid lands on any large scale.
Aboriginal peoples were never so “simple and primitive” as we have been led to believe by the literature of their invaders.
Native agricultural and pastoral management practices are often finely tuned to survival, are sometimes very productive, and above all are independent of outside aid.