Using the Relationship between Rate of Tatter and Topographic Variables to Predict Site Windiness in Upland Britain

Tatter flags have been used for more than 30 years to measure wind exposure of forest sites in upland Britain. A re-analysis of tatter flag data from 1111 sites was performed to investigate factors influencing site windiness. At each location flags had been flown for periods of 2 months, and six consecutive bimonthly readings were combined to provide an annual estimate of tatter. Average daily tatter rate was related to geographic position, aspect, elevation, topex, valley shape and valley direction. The aspect, valley shape and valley direction were all derived from the eight topex sector values; they provide a more detailed treatment of topography than previous studies and include a measure for funnelling of wind in valleys. The proportion of variance explained by the regression was 80 per cent. The regression has been used to develop revised windiness scores for the Windthrow Hazard Classification and could be used to estimate site windiness for site-yield and related studies. Digital terrain models can calculate the required site variables. Further investigations to improve the estimates are discussed.