What's New at Oregon Viticulture

19 November 2007

Both the Windows and Macintosh versions of GDDCALC have now been validated for sites in southwestern Oregon. In other words, you can use the program to calculate GDD for all Oregon sites west of the Cascades and north of the California border which also meet the maximum elevation criterion (500 meters). The program is also valid for sites in southwestern Washington.

In addition to assimilating data from southwestern Oregon, we have removed a bug associated with the year 2000. (Yes! A Y2K issue, but not the one you think.)

This newest version of GDDCALC is Version 0.8 and is the version you will get when you download it from this website.

28 August 2007

The Windows version of GDDCALC has been upgraded from Version 0.7 to Version 0.71. Certain issues around the placement of text have been resolved in the newer version.

13 July 2007

The Macintosh (actually, OSX) version of GDDCALC is now available from the downloads page.

11 July 2007

Minor changes to the software have resulted in an upgrade from Version 0.61 to Version 0.62. These are the versions now offered here. A Macintosh version of the software will be put up in a week or so.

13 June 2007 - Global Warming Issues

Recently there has been a great deal of discussion about the effect of global warming on harvest times in the Oregon wine country. See, for example, the recent treatment of the issue on the OPB program Oregon Field Guide. In an attempt to get beyond anacdotal evidence we decided to look carefully at temperature data from 21 stations in and about the Willamette Valley. Our measurments were obtained from OSU's Oregon Climate Service and most cover a period of 46 years, from 1961 through 2006. We divided the data into two groups, the first 23 years of that period and the second 23 years. At each station we applied Student's t test (p. 185, Burrington and May, 1953) to see whether the mean values of GDD in each 23-year period were different at the 0.05% significance level.

The somewhat surprising result is that at most stations and during most months there is no reason to believe (at the 0.05% level) that the earlier and later GDD values are from different populations. The principal exceptions are during midsummer at some stations (July, August, September) where temperatures have indeed been higher in recent years. At several locations midwinter temperatures (October through February) have actually been lower recently, but not significantly so.

Specifically, in July eleven of the 21 stations show a statistically significant warming trend. In August nine stations display a warming trend. In September four stations have been warmer in recent years. It appears that our subjective impression that recent summers have been warmer is correct.

Because mid Summer and early Fall are critical in viticulture, and we have found a warming trend at some (though not all) Willamette Valley stations during this critical period, we have decided to revise our model by giving greater weight to recent years in the equations that connect insolation to growing degree days. As a result GDDCALC now produces a slightly higher value for GDD during the growing season. The version of GDDCALC that implements this change has been designated 0.61 and is the version now available on our downloads page.

27 April 2007

The website is now well under way. The Windows version of GDDCALC is now available here - both the executable and the source code. The executable is known to work under Windows 2000 and some earlier versions of Windows, but nothing is promised with regard to later versions (XP and Vista). If the executable does not do well with your version of the Microsoft operating system we invite you to download the source code and recompile or redesign it - this is Open Source software.

At the present time GDDCALC is validated for the Willamette Valley and environs, and southwest Washington. It will reject queries for sites outside that region. Our plan is to gradually expand the region for which GDDCALC is valid. Stay tuned. We will announce progress here, on this page. When GDDCALC is modified you will be able to download new versions. The present version is designated 0.6.

You can email us at this address. As with any open source project, we appreciate and encourage bug reports.