Over the weekend a friend told me about an article relating climate in Bordeaux, France to Bordeaux wine quality.    The article is “Bordeaux Wine Vintage Qaulity and the Weather”, published by the American Statistical Association in 1995 and authored by Orley Ashenfelter, David Ashmore,  Robert Lalonde.    The basic premise of the paper is that understanding the weather conditions in Bordeaux is an excellent indicator of the price of top growth wineries from Bordeaux (and therefore quality — i.e. there is an efficient market for wine).        

What a paper!    The paper really got the creative juices flowing and helped consolidate my  long term goal for this blog.  Namely, to monitor climate in Virginia and use it as a discussion piece for the likely quality of Virginia, Albemarle County, and Charlottesville Wine as a year develops.  

From what I can tell surfing around the web, the paper created quite a ruckus at the time it was published.  If weather is a major determinant of quality, for what do we need all the wine expert comentators?       It turns out that Dr. Ashenfelter created a publication called Liquid Assets,  which discusses wine as an asset.   On that site, he has updated the orginal paper with more recent results. 

 More importantly for this post,  the site also provides tabular data from the article.    As there was a time in my former life when I was a scientist,  I can’t help but try to 

1) Recreate the results of paper (accomplished easy enough in MS Excel)

2) Try to extend the results based on the data available,

3) Apply the results to other regions gowing wine (Napa,  Washington, Australia, and, oh yeah, Virginia). 

 

The article relates weather data to Bordeaux wine prices.    So,  let’s get some weather data.    It turns out that the National Climatic Data Center makes the Global Historical Climate Network – Daily Data avaiable for download.    

Based on the data from Bordeaux,  a question becomes immediately obvious.   What surface temperature data was used in the paper?

 

A temperature comparision to Ashenfelter et al., 1995 and GHCN Daily Data

A temperature comparision to Ashenfelter et al., 1995 and GHCN Daily Data

 

In the time series graph,  I compare the time series of  April to September  averaged data for each year  from the Bordeaux weather station available from the data set.   As can be seen, the time series are very similar but not exactly the same. There is a slight warm bias in the GHCN data.  The red line is the temperature data from the Ashenfelter et al. paper whereas the blue line depicts the temperatures directly from the GHCN daily data.    I’d be interested in knowing the exact source of data used by Ashenfelter et al. (in the vein of scientific reproducibility).   What could cause the difference in the time series?

1) Quality Control — I have applied no quality control to the data I extracted from the GHCN data set.  However, NOAA has extensively QC’d the data. 

2) Trend correction –  There are many efforts to correct temeprature and related time series for trends attributed to climate change  that have appeard in data over the last 50-75 years.   The fact that the blue (GHCN data) tends to gradually rise above the red line (the papers data) suggests to me that it may, in fact, be “trend corrected” data.   

3) A different station is used –  I have not yet extensively researched the availability of weather station data from Bordeaux.  It could be that the GHCN daily station (which is the airport data in Bordeaux) is different that the data actually used by Ashenfelter et al.        For those who don’t know about European Weather Data, unlike in the United States,  weather data is generally restricted and difficult to obtain.     I don’t hold out hope that if a different station has been use,  I’ll be able to get it.

 

By tracking down the weather data from Bordeaux, I’m hoping to be able to extend the results a bit.  Maybe the early season temperatures are more important than late season.   Maybe a heating degree day type formulation improves the model.     The issue above does not prevent me from looking at these questions, but it does complicate the issue a bit.         I’ll be searching for answers however.