This is an elevation map for New York State. Elevation data has not been included in the state scale analysis because of the technical problems with processing the data volume. Important topographic factors include air drainage, aspect, slope and localized lake influences. Air drainage is a critical factor for good vineyard sites, as it allows cold air to move down slope and be replaced by warmer air from above. Topography has a major influence on air drainage.. Slopes help to remove cold air but closed valleys and hollows increase the risk of cold injury (Dry and Smart 1988). Even a few tenths of a meter in elevation may make a difference in minimum temperature in the order of 1.8oF (1oC) (Geiger 1965). Geiger (1965) reports a study by Reiher who estimated that air current flows at less than 1 m sec-1 and are easily disrupted by any obstructions. A concave surface is more frost prone than a convex surface. A 1 - 3% slope is often quoted as a minimum figure for useful air drainage (Jordan et al. 1980, Macgregor, D. personal communication), but the basis for such an estimate is unclear. Excessive slopes however are not beneficial for machinery access. Jordan et al. (1980) suggested machinery access on slopes up to 12% are optimal, satisfactory on 13-18% and difficult over 19%. Slope alone however is not the sole indicator of air drainage potential as sloping sites may have poor air drainage if they are pooling or closed valleys. Obstructions such as fences or windbreaks may also inhibit air drainage. Aspect is usually important in site selection studies both in terms of shelter from prevailing winds and interception of solar radiation. Its importance in NY however is unclear (N. Shaulis personal communication).
Methodology for construction of this map
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