Bob,
These maps are interesting somewhat. I live in NW FL zone 9 on Arbor Day map. Well, ironically, Tampa is also in zone 9 for the 2006 map! The climate is markedly different between here and there--at least a zone or more, I'd say.
All these maps are based on(to my understanding) is the actual low temperature for a given year, averaged over a 10 year(?) period. For example, the map of 1990 would be ab average of the low temps from 1980-1989. Or do they do a longer average?
In the 1990 map, I am in zone 8. I believe because our record lows in Dec 1983 and Jan 1985 skewed the results of the prior period because it was around 11 degress in 1983 and about 6 in 1985. (Last season's low was 18--which I consider about average.) The period from 1990-1999 didn't see any lows near 11 degrees--muchless 2 years of the 10 year period near single digits. This can materially affect the average. Remember also that it only takes a 1 degree average difference to change 1 zone(on paper) if your average low is near 20 degrees----the breakpoint. Zone 8 is defined as 10-20 degrees. So for many years, I have often said that I live in zone 8 1/2(which is borderline 8/9).
Another factor to consider when using the USDA temperatures is the fact that many of the reporting stations are now in urban areas that used to be rural. Urbanizing can increase the temperatures recorded by a degree or 2-----making it look like "GW", when it really isn't. It's a change in the surroundings of the measuring devices, instead. (instead of "GW", we have "overlooking something right under our noses"--which happens often these days, it seems.)
Regards,
Richard Harrison, NW FL
I'll get the email address of the researcher who spoke in LA last month who had the USDA zone charts and ask what year's chart he had to see if he supposedly had one since 1990. Personally, I believe I have seen 3 since I started growing fruit about 1977 or so. I COULD have been seeing an "old" USDA chart then, maybe they came out with a new one about 1980 and another in 1990. I'm not sure. But I'm pretty sure that I have seen at least 3---usually published in nursery catalogs.
--- On Mon, 8/3/09, Bob Randall <YearRoundGardening@comcast.net> wrote:
From: Bob Randall <YearRoundGardening@comcast.net>
Subject: Re: [NAFEX] California's screwed tree crops
To: "North American Fruit Explorers" <nafex@lists.ibiblio.org>
Date: Monday, August 3, 2009, 12:57 PM
As best I can determine, the USDA has not updated its zone chart since 1990, though they are said to be working on it. However, others have. See the National Arbor Day site http://www.arborday.org/media/map_change.cfm
They conclude that things nationwide have been getting warmer as far as zones (see their maps). It would be interesting if the USDA has opposite results since presumably they are using the same temperature data.
I have been looking at the situation in the Houston area for many years since it became obvious that the zone info and chill info was off base in helping people select fruit trees over diverse climate ranges. Based on a large number of online area airport weather readings, it is very clear that the Houston area has gotten warmer since the last really cold weather in 1989.
For whatever the weather data are worth, the last 20 years have been the warmest winters and summers in the last 140 here. However, the period from 1969-1989 was the coldest, but closely tied with a period in the 19th century. So obviously, other factors (volcanic activity?) than greenhouse induced global climate change affects how cold or hot it gets in a decade.
For whatever it is worth, parts of Houston area are in zone 10 (using averages), and coastal areas like Matagorda and Galveston are even in zone 11 some years while averaging 10b. See my data summaries (which are easy to check through NOAA and other sites) at http://www.urbanharvest.org/advice/basics/weather_data.html .
"Share What You Grow and What You Know!"
Bob Randall, Ph.D.
713-661-9737
On Jul 24, 2009, at 12:29 PM, Richard Harrison wrote:
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Ginda,
I don't want to "fight" about GW, either, but wanted to point out that the USDA zone chart(which indicates the minimum temperature of Winters) shown by the speaker at the fruit meeting in LA recently indicated the zones had actually expanded Southward, rather than Northward. So this is cooling, not warming. However, no one predict the future with any degree of accuracy.
Yes, I agree, some areas may be on a warming trend and others in a cooling trend, temporarily. Personally, I didn't care for the negative sound of the topic title--and after looking at the link discovered flaws which affected the controversial conclusion(title of post).
I consider it very questionable if not misinformation---even if it was written by Ph D's.
From: Ginda Fisher <list@ginda.us>
Subject: Re: [NAFEX] California's screwed tree crops
To: "North American Fruit Explorers" <nafex@lists.ibiblio.org>, "nafex@lists.ibiblio.org" <nafex@lists.ibiblio.org>
Date: Friday, July 24, 2009, 8:49 AM
Sure, I don't want to fight about global warming today. I do want to elaborate a little on the prior post, from Richard Harrison, asserting an increase in chill hours in some warmer states.
That's not inconsistent with global warming. My understanding is that chill hours are not hours when it's really cold, but are only hours when it's sorta chilly (near or above freezing, up to 40 or 50F), when the trees are metabolically active but 'feel cold'. I gather that in very cold places the native trees don't need a lot of chill hours, since they have to come out of dormancy quickly and do their thing. It's places with long bumpy springs and late frosts where the local trees have adapted by needing a lot of chill hours.
So if global warming is linked in some areas with a longer spring, you could easily get both higher average temps and more or similar chill
hours.
Also, the US is a large country with lots of climate zones, some quite chilly. Surely agricultural plantings can move north if we get even quite a lot of global warming. Concurrant disruption of rainfall patterns is a more serious agricultural threat, but I'm sure the US will continue to be able to grow food _somewhere_, however cliate change plays out.
-- Ginda
Alan Haigh wrote:
Please members, can we refrain from another fruitless debate on global warming?
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