Geographical and geomorphological effects on air temperatures in the Columbia Basin's signature vineyards
By Liesl Olson
Whitman College, Walla Walla WA
The Columbia Basin in southeastern Washington and Oregon is one of the most productive grape-growing areas in the United States. It is bordered by the Rocky Mountains to the east, the Cascade Mountains to the west, and the Columbia River to the south. The region contains ten American Viticultural Areas (AVAs). A variety of geographical and geomorphological factors affect air temperatures within these AVAs. Air temperature is an important factor in understanding the terroir of a particular vineyard.
Air temperatures were measured for a year at 60 Columbia Basin vineyards, which have been recognized for producing high-quality wine. These hourly temperature records were used to compute various climate statistics, including average air temperature, average diurnal temperature range, growing degree-days, average maximum temperature, and average minimum temperature. These parameters were plotted against the vineyard’s elevation, latitude, slope, aspect, and relative lowness coefficient (RLC), in an attempt to determine their relative influences on air temperatures.
Within the Columbia Basin, average air temperatures are controlled primarily by elevation and proximity to large bodies of water. Other temperature statistics, including average minimum temperatures and diurnal temperature ranges, are influenced by relative topography like slope and RLC values. While these factors explain some of the temperature variability between AVAs, other geomorphological elements may be used to explain air temperatures.