June 2013 Issue of Wines & Vines
Topography and Temperature
Research in Columbia Valley links land and growing degree days
Rivers and mountains define many of the world’s great wine regions, and the West Coast of North America is no different. The Columbia River winds its way south from British Columbia through Washington state; the Willamette River carves a home for Pinot Noir through Oregon, and the Russian River flows through Mendocino and Sonoma vineyards in California on its way to the Pacific Ocean.
But understanding how those rivers—and the topography of the valleys they’ve shaped—influence vineyards is a question with few obvious answers. While the moderating influence major watercourses play on temperature is well-known, as is the potential for valleys to draw in cold air, generating fog banks above the waters, Kevin Pogue of Whitman College in Walla Walla, Wash., has spent the past two years gathering data that could improve growers’ understanding of local topography—leading to more knowledgeable site selection and better vineyard management.
What the research is
Pogue, a geologist, has a long-standing interest in the terroir of the Columbia Basin. He presented a paper to the VIII International Terroir Congress in Soave, Italy, in June 2010, focusing on the influence of the region’s basalt-rich landscape on vines, specifically soil temperature, cluster temperature, vine chemistry and other attributes. That same summer, Pogue covered 1,400 miles deploying data loggers at approximately 55 vineyard sites across the Columbia Basin with the intention of gathering data related to vineyard temperatures.
Pogue wanted to see if there were links between topography and the accumulation of growing degree days (GDD), an indicator growers use to predict the key stages of fruit development including bloom, véraison and crop maturity. The number of growing degrees for any particular day is the day’s average temperature in Fahrenheit minus 50. (For example, a day with an average temperature of 70ºF would log 20 GDD.)
The data loggers, the Hobo model produced by Onset Computer Corp., cost approximately $125 apiece. The units record data, which Pogue then had to download (systems that transmit data wirelessly cost closer to $1,500 apiece).
Pogue tested the data loggers for consistency prior to placing them in vineyards at a height of approximately 6 feet. All locations were in vineyards to secure relevant readings; locations were away from overhead sprinklers, asphalt and anything else that could distort the readings.
The units stayed in place from August 2010 through the end of 2012, giving Pogue data about one of the coolest growing seasons on record—2011, which racked up just 2,312 growing degree days—as well as 2012, which at 2,643 growing degree days was about par with the long-term average of 2,628 growing degree days.
What the research found
Pogue is just starting to work through the numbers, but the preliminary findings are providing a clearer picture of how growing degree days accumulate, and a better understanding of why vineyards respond differently to weather systems.
“People tend to look at daytime high temperatures (and say), ‘Oh yeah, it’s hotter here, I was out there yesterday; it was 104ºF, this is a hot site,’” Pogue says. “But when you add up just the heat units, that’s also a function of how warm your low temperature is.”
What the numbers indicate (counter-intuitively) is that higher elevations aren’t always cooler, especially in areas such as the Yakima and Walla Walla valleys.
The Yakima follows a deep, narrow course as it flows east, past the northern base of the Horse Heaven Hills and around Red Mountain to enter the Columbia River at Richland, Wash. More dramatically, the Walla Walla River descends from the Blue Mountains and joins the Columbia north of the stunning Wallula Gap. While the valleys themselves are broad, the exit points are effectively bottlenecks that limit air drainage.
These “are fairly broad basins that have fairly narrow exits,” Pogue says. “It forces cold air to pool in those valleys. Farmers in both valleys have known that for a long time.”
But the pooling of cold air also suppresses the accumulation of growing degree days because air temperatures have to warm up—a hurdle that vineyards above the pool of cold air don’t face.
“You get morning low temperatures that are pretty cold,” Pogue says. “It takes longer for those areas to warm up in the mornings, and (while) they might eventually reach a higher temperature than some of the higher elevations, it doesn’t get rid of that morning cold effect.”
The length of the growing season in a vineyard affected by the pool of cold air and in unaffected vineyards can differ by as much as a month. Les Collines vineyard in the foothills of the Blue Mountains, for example, racked up 3,256 GDD in 2012 at an elevation of 1,358 feet; but Pepper Bridge, at 784 feet, had just 2,663 GDD. Both are in the Walla Walla AVA.
Similarly, the warmest growing areas Pogue tracked have no impediments to the drainage of cool air. Air temperatures are consistently warmer du ring the growing season, thanks in part to the moderating effect of the Columbia River, which releases heat during the cool nights.
Areas such as the south side of the Horse Heaven Hills consequently racked up some of the longest growing seasons in the state. The longest was seen at a block on the Wallula Benches, at a very low elevation where the Columbia River forms Lake Wallula behind the McNary dam. It racked up 265 frost-free days in 2012 between the end of February and December.
“I was shocked,” Pogue says. “It had this incredible nine-month frost-free period.”
But on the back side of the valley, away from the river, it’s a different story—as highlighted by the frost damage in November 2010, when some areas were hit with temperatures as low as 0ºF. Under normal circumstances, conditions were right for a steady senescence and hardening off of the vines, but the sudden frost was too much, too soon.
“It wasn’t absolutely that cold, but it was too early,” Markus Keller, a professor of viticulture at Washington State University’s Irrigated Agriculture Research and Extension Center in Prosser, told Wines & Vines the following spring. “The vines hadn’t fully acclimated yet when it happened.”
But the damage wasn’t uniform across the state. Vineyards in the Yakima Valley were largely unscathed while many in the Horse Heaven Hills were hit hard.
Pogue’s research suggests that topography may have had something to do with how vines respond to cold weather throughout the year. Vines that are accustomed to colder daily minimums—namely, in vineyards that are beset by the cold air pool—won’t suffer as much as vineyards above the cold air pool or those where temperatures are moderated by the Columbia River.
“If you have a cool year, if you have a higher elevation site, you’re going to feel it more than a lower elevation site,” he says. “The low sites that were affected by cold air pooling were pretty much the same.…It more strongly affected the higher elevation sites.”
Better site selection
A better understanding of how air is moving through the Columbia Basin could ultimately lead to better site selection. The right site is a key element in reducing environmental risks, but understanding how topography relates to specific differences in air temperature will give growers greater data to work with when choosing sites by putting hard data behind growers’ experience.
“What would be the coolest thing in the world to do would be to come up with this equation for the Columbia Basin,” Pogue says. “You could have a little parameter for each of the different variables, and you could plug some numbers into this equation and it would spit out what your computed growing degree days would be in an average year. That would be the Holy Grail.”
Measurements of GDD are a basic method for determining the suitability of sites. They’re “extremely crude in terms of what’s happening,” says Co Dinn, director of winemaking at Hogue Cellars in Prosser. But Pogue’s efforts to combine the readings with other information point a way forward.
While systems such as Washington State University’s AgWeatherNet are helpful in providing more detail, Dinn is excited by the fine grain of information Pogue’s monitors are gathering.
“We have that information (from AgWeatherNet), which is great, but as far as every 15 minute-type data point gathering in individual vineyard blocks, that’s being made possible by the advent of these new, relatively inexpensive data loggers,” he says. “It’s more information, and that’s information that was very hard to gather.”
Dinn believes that temperature patterns and GDD provided by the data loggers will give growers the kind of information they need to manage sites better.
“A lot of vineyard sites are relatively new, and I think Kevin’s on the front end of the curve in terms of measuring these sites,” Dinn says. Pogue, for his part, believes the data could also open new areas for vineyard development.
Data loggers in the foothills of the Blue Mountains east of Walla Walla have garnered readings that suggest long, if cool, growing seasons. While the heat accumulations aren’t as large as at river-front vineyards, the number of frost-free days is encouraging. There’s also no need to irrigate, making for more efficient vineyards.
“They start to look like Burgundy or the Mosel,” he says. “There’s potential if you move to higher elevations to limit your frost risk and have more balanced wines.”
The question, however, is whether Washington state growers want to grow cool-climate wines reminiscent of Burgundy or Mosel, or if they want to continue to hitch their wagons to the big reds that have made the state’s reputation for high-end wines.
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