Climate Zones.

Rodger Whitlock
Thu, 27 Oct 2005 22:05:36 PDT
On 27 Oct 05 at 10:41, John Bryan wrote:

> I wonder what your opinions are about the USDA Climate Zones.
> I also wonder why such zones cannot be linked with our zip
> codes, or postal zones. Would they not then be better defined?

The USDA zones were devised to assess the winter hardiness of 
woody material and are based solely on average winter low 

They are not, iow, *climate* zones. Climate involves a great 
deal more than just the winter low temperatures.

For example, consider rainfall. Not only is the annual rainfall 
important, but also its distribution over the course of the 
year. We get abt 20" of rain a year here, but it mostly falls 
in the Dec-Feb period and our summers, though cool, are usually 
bone dry.

The same amount of water spread out over the year would give 
entirely different growing conditions. Concentrate it in the 
summer, not the winter, and we might even be able to grow those 
touchy east Asian plants that, if they don't desiccate into 
nothingness in August, rot away in February. (Tricyrtis in 
Victoria? A complete failure in my former swamp.)

Other factors: wind; exposure to sudden sharp outbusts of 
severe weather (as in Portland, Oregon when vileness swoops 
down the Columbia River gorge or here, where we get "arctic 
outflows" of seriously cold weather). Also summer heat units 
(degree-days) and length of growing season (frost-free period).

And others.

Even your exposure affects climate: the north side of a hill 
often has a very different climate from the south side.

Rodger Whitlock
Victoria, British Columbia, Canada
Maritime Zone 8, a cool Mediterranean climate

on beautiful Vancouver Island

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