Beware the Law of Averages

I am a devoted follower of wine-critic Robert Parker and his Wine Advocate newsletter, the most recent edition of which showed up in my mailbox on Monday. It contains the first dispatch of four comprising the newsletter's big Northern California report. The balance of three reports will follow in subsequent editions of the newsletter over the coming winter months. Although Lord Parker has assigned other wine regions to subordinate critics, he holds on to Northern California (and, I suspect, Bordeaux, as well).

As with all his reports, Parker devotes considerable space to retracing the weather during the growing season, often going into great detail on rainfall and temperature. It is detail that for obvious reasons now holds more interest to me than in the past.

The current report covers three vintages—2012, 2014 and 2014—and goes into great detail on the weather during the growing season and harvest for each vintage. At one point, Parker refers to graphs of weather conditions during the growing season. Apparently, graphing weather conditions is SOP for real viticulturists. And with 100 vines, I thought it appropriate to act like a real viticulturist and do my own weather graphs for my vineyard.

The First Month

I don't know for sure how typical 2015 has been, although when compared to the historical averages it appears we have had shortages of rainfall during some periods, and an abundance of precipitation in others.

This was apparent in May, soon after I completed planting all the grapevines. I finished planting by the end of April, and was promptly greeted by a very dry May. Normal rainfall for May is around 3.5 inches. You can see from the graph we had less than an inch for the month, which is the recommended amount for a grapevine each week.

The attached charts are from a USGS website that accumulates rainfall totals real time from stations in the Charlotte area. These stations report rainfall on an hourly basis and give running totals by the hour and by the day for a rolling seven day period. The website also allows me to query the historical data for any period from Oct. 1, 2007 to the present. The data most useful for my purposes comes from a station labeled White Farm, about a mile from my house. I don't actually know where the station is located, but I plan to someday scout the location and find out. One thing I appreciate: the site alleviates the need for me to get a rain gauge and faithfully collect the data, compile it and create similar graphs.

The short version of May is it was very dry. Unseasonably dry. So dry that it forced me to water the grapevines every few days, dragging 200 feet of hose around the vineyard. It was a two-hour exercise and only marginally effective because of the runoff.

June 2015

June rainfall amounts returned to a more normal pattern, with  fairly regular rainfall during the month and a cumulative total of about 3.6 inches. Unlike May, which had rain on only three days, there was better distribution, with some rainfall every week.

There was little need for me to hand water during this time, and the vines got their recommended one inch of rain each week.

July 2015

July was similar to June, We got about 3 inches of rain during July, but there were a few weeks where the requisite one inch failed to materialize. Thankfully, the drip irrigation system went live July 11, and took care of the long gaps in precip. The vines were vigorous and putting on substantial growth that required plenty of water. Between the rainfall and the drip system, the vines continued to flourish.

There was nothing unseasonable about the weather up to this point, which was much nicer than what I have been accustomed to in Texas. I remember many a July in Dallas with many days topping 100 degrees with no rain in sight. (I guess I will need to find daily temperature data to go with this rainfall record to make my vineyard journal complete.)

August 2015

August would have been a disaster without the drip system. The total for the month was about normal, but the bulk of the precipitation came in one 24-hour period. Although the month topped out at just over 4 inches, there was only a trace amount for the first 19 days of the month. On Aug. 19, we got a monster storm that dumped about 3.5 inches on us in a 24-hour period. Without the accompanying graph, I would have been tricked by the "Average Rainfall" gremlin and the dishonesty of averages.

August would have been terrible without irrigation, which got plenty of use at the beginning and the end of the month. I need to look at the temperature data to get a better picture of what was going on. I do know, however, that August in North Caroline is far more tolerable than August in Texas.

September 2015

September followed the same pattern as August, with no rain for the first two weeks. The first rain didn't show up until the middle of the month when 1.5 inches fell over two of days. Nearly two weeks later, there was an additional 2 inches to bring the total up to the norm of about 3.5 inches. The irrigation system got a little work during the month to keep the vines healthy.

September would be the last time I had to resort to watering, as October ushered in one of the wettest months on record in the Carolinas.

October 2015

We got nearly 8 inches of rain in October from two monster storms that included one that ultimately stretched from Winnipeg to Cape Cod before moving off into the North Atlantic. It seemed to rain every day from Oct. 2 until Oct. 11, accumulating more than 6 inches of during that period. The ground was saturated, with water standing  four inches deep in numerous places on our property. The gentle slope in the vineyard preventing standing water there,

During that time, South Carolina suffered Biblical flooding through much of the central part of the state, displacing thousands and resulting in a number of fatalities. We got hammered near the end of the month by another storm that dumped 2 inches on us in a 24-hour period.

With six months under our belt, there is ample evidence that the law of averages can lead to erroneous conclusions. Although five of the six months had normal rainfall (October was far wetter than normal) June was the only month that distributed the rainfall over the entire month. The other months (even October) proved truth to the old saying "when it rains, it pours."

November 2015

This has been a wet month, with rainfall nearing 10 inches for the month. The ground was already saturated from the heavy rainfall in October and remains so as we move into December. I'm not sure what that will lead to in the spring.

One impact of all this rain is my plan to build the trellis system this fall has b een overtaken by events. The ground is too wet to work and pushes the construction effort into the new year.