Friday, October 20, 2017

Virginia wine: The physical environment

I recently visited a number of Virginia wineries with Frank Morgan (Drink What You Like) and will be reporting on those visits in upcoming posts. Prior to those posts, however, I will attempt to familiarize readers with the physical environment within which the region's grape growers operate. I will begin with the landscape, given its role in shaping the state's climate.

Virginia Landscape
With the exception of alluvium and wind-blown soils, an area's soil is derivative of its underlying rocks. As shown in the charts below, Virginia, as a result of long-term tectonic, orogenic, erosional, sedimentary, and intrusional activity, is divided into five major geologic zones. The first chart describes the formation and characteristics of each zone while the latter identifies the rock types included in each zone as well as its period of deposition/intrusion.


Virginia Climate
Climate, according to Dr. Tony Wolf (Lecturer and Viticulturist, Virginia Tech) and John D. Boyer, is the average course of weather in a region over an extended period as measured by temperature, precipitation, and wind speed, among other variables (Vineyard Site Selection, Virginia Cooperative Extension).  Weather is itself defined as the state of the atmosphere at a specific point in time using the same variables as referenced in the climate definition above.  The climate of a grape-growing region will determine, to a large extent -- and all things being equal -- both the grape varieties that can be grown and the styles of wine that can be produced. The climatic requirements for successful viticulture include: a growing season long enough to mature both the fruit and vegetative aspects of the plant; production of sufficient carbohydrates to ripen the fruit as well as to maintain future productive potential; and an adequate supply of water.

Virginia's climate is officially described as humid subtropical but, in reality, it has one of the most complex climates in the US. This complexity is reflected by the fact that the state is divided into five climate zones (The figure below actually shows six zones because it breaks Piedmont into eastern and western portions).

VA climate zones: 1 - Tidewater; 2 and 3 - Piedmont;
4 - Northern; 5 - Central Mountain; and 6 - Southwestern Mountain
According to the University of Virginia Climatology Office, "Virginia's climate results from global-scale weather patterns that are modified by the diverse landscape of the Commonwealth." The following two charts show the manner in which these global-scale weather patterns are modified within the Commonwealth. The first chart shows two temperature modification events. The first is associated with winter storms. These storms work from west to east across the state and turn northeast when they encounter the Gulf Stream. Moisture-laden air from these storms are then blown onto land from the east and northeast, with most of the rain ending up on the eastern slopes and foothills of the Blue Ridge Mountains.

The second event is the classic rain-shadow effect where winds from the west encounter the Appalachian Mountains and dumps moisture on the western slopes of that range as they climb while eastern winds encounter the Blue Ridge Mountains and act accordingly. As shown in the figure, the regions between those mountains are the driest in the state.

Derived from
The water falling on the state is drained off by an extensive riverine system. The workings of this third climate modifier is shown in the figure below.

Acording to Jim Law of Linden Vineyards, Virginia is one of the wettest viticultural regions on the planet. The chart below shows the trend of VA average annual precipitation between 1895 and 2010 and the trend is towards increasing levels statewide. The table below the chart shows the distribution of that precipitation by climate zone.

Trend of VA average annual precipitation, 1895 - 2010

Climate Zone Annual Average Rainfall (inches) January Average Temperature (F) July Average Temperature (F)
35 - 48 71 - 85
27 - 47 68 - 88
Northern Virginia
19 - 42 61 - 86
Western Mountain
27 - 45 65 - 87
Southwestern Mountain
24 - 44 60 - 85

As shown in the table above, the average annual rainfall in Virginia ranges between 38.29 and 47.33 inches per year. Contrast this with Napa which receives an average of 20.39 inches, less than half of the rain that Virginia receives. The problem with that much water is that it requires the right type of soil and slope in order to allow proper drainage of the vineyard. Some grape varieties do not like wet soils while too much water does not allow for stressing of the vines, a key requirement in growing high-quality red wine grapes.

In a May 2012 interview with Dr. Bruce Zoecklein, then Professor of Enology at Virginia Tech (and former State Enologist), he told me that Virginia winemakers had to deal with late frosts, drought, high humidity, and tropical storms in the fall and that they needed to continue working to understand these phenomena and then to incorporate their learnings into their viticultural processes.

Virginia Wine Regions
The Virginia Wine Board Marketing Office (VWBMO) provides a map which divides the state into various wine regions and then indicated American Viticultural Areas (AVAs) within those regions. I used such a map as the basis for a graphical presentation of the characteristics of each region (see below).

During the compilation of chart, I became curious as to the genesis of the wine region map and pursued answers along a number of paths. Frank Morgan was finally able to get me a response from Annette Ringwood Boyd of VWBMO which stated that the regions were determined by Virginia Tourism and, when VWBMO started 10 years ago, they "used these so that there would be continuity in how people were talking about Virginia regionally." According to Annette:
As they have added regions, we have mimicked them to continue that seamless presentation of Virginia. One of the strong arguments in support of this strategy is that 60% or more of VA wineries are not in AVAs ... In addition, in 2009 or 2010 we added Virginia AVAs to begin to add wine specific regions to our map. To date this is still imperfect, but long term, this is how we would like for the regions of Virginia to be defined. Until the AVAs are more inclusive, we will use the VTC regions of Virginia.
In other words, the Virginia wine regions, as currently configured, is a marketing contrivance with no undergirding viticultural rationale. While this will work for a tourist-based wine economy, it will force us to continue to look to individual wineries to determine high-quality wines because comparisons within and across regions (outside of the AVAs) are essentially meaningless.

©Wine -- Mise en abyme

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