| Richard,
I've been out of computer range for awhile. Sorry to delay this response. I'll try to respond to the issues you raise. You said
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. |
I'm not surprised. I don't like the USDA zone concept at all, and it is close to useless for serious tree work in a borderland semitropical area like the Upper Texas Gulf Coast where we are growing guavas, mangoes apples, papayas and pears, and where temperatures change not only with degree of urbanization and distance from the coast (not even considering long run changes).
The data I published at are designed to deal with a range of weather data--such as the local range in the number of frosts, date of frosts, low temperature, chill, etc. and help people who are both in very urban settings like central Houston and very rural areas far from the coast like Willis (where Leon Atlas tested many apples and pears in the 1980's.) They are not averages--rather percentages of years when different conditions held. Richard, you (or someone else) could extend low temperatures to the last 40 years in your area if you have the time and find the archive data, and make a table based on percentages where the yearly low was below 8˚, 12˚, 16˚, 20˚, etc..
The zone maps as I understand them are based on the mean-average low temperature recorded over the last 20 years. Since the period from 1970-89 was the coldest 20 years of winters in our area (and Gulf Coast at least) in the last 140 (because of the 1980's freezes, El Nino, low mean temperatures and much else--volcanoes?), it is quite possible and even probable that the zone changes are related to the difference between the decades and as well urban heat island. They also may be related to global warming (which is measured from satellite area sampling in the lower?? atmosphere I think), but it may take decades to see just what this means and how bad it is. My data show that the Houston area 5 month summers have been in the last 20 years by far the hottest (in monthly averages) in the last 140 years, so our irrigation situation and plant stress issues have been accelerating.
I would suggest that anyone who is wondering what the weather situation is like in their area during recent decades (whatever the cause), go to the NOAA website http://forecast.weather.gov/zipcity.php and put in your zip code, then use that link to track down archival data from your area airports on weather from the last decade or two. This is tedious work (winter low temperatures are reported by calendar year--not winter (which straddles two calendar years). At least it will tell you what has really been happening in your area at airports. If you think your data is much different from the airports' data, compare what your readings are with theirs on a series of cold and warm nights and adjust their data to your personal case
I tried entering temperature february 1980 Galveston TX and instantly got a result for the average, minimum, and maximum
However, if you pick a place without data for that year, you get the nearest national weather service station where data is--and it could be at considerable distance from what you entered.
Bob "Share What You Grow and What You Know!"
Bob Randall, Ph.D. 713-661-9737
On Aug 3, 2009, at 3:26 PM, Richard Harrison wrote: 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.
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: | 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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