Cold-Air Pooling in the Upper Douro Valley: An Observational Study

Abstract

Cold-air pools can have several different impacts on viticulture, including final grape quality and yields. This study focuses on cold pools in the upper Douro Valley, which is one of the most important viticultural regions of northern Portugal. First, digital elevation model data were analyzed to identify pixels corresponding to the valley floors of the Douro and selected side valleys. Next, the topographic amplification factor was calculated for each of these pixels. Down-valley gradients in the topographic amplification factor were used to identify locations where cold air in the valley was likely to pool. High-time-resolution meteorological data recorded between January 2011 and December 2017 were analyzed to identify cold-pool events at one location in the main Douro Valley. The cold pools were assigned to seven different categories on the basis of their temporal behavior. There was a clear seasonal cycle in numbers of cold pools, with most observed during winter and the fewest in summer. The maximum strengths of the cold pools could occur at any time during the night, although the majority peaked around the middle of the night. This study is believed to be the first to examine cold pools in the upper Douro Valley.