Using GIS to determinate a suitable areas for avalanche occurrences in the Presidential Range, New Hampshire, USA Silvia Petrova Objective Several factors may affect the likelihood of an avalanche including weather, temperature, slope steepness, slope orientation, wind direction, terrain, vegetation and snow pack condition. Different combination of these factors can create a low, a moderate or an extreme avalanche condition. The objective of this project is to use Geographical Information Systems to map avalanche risk zones in the Presidential Range in the White Mountains in New Hampshire based on topographical and vegetation parameters. The DEM, with 30 meter resolution, has been used to create topographic variables such as slope, aspect and to extract runoff accumulation per pixel. Land use map from 2001 has been used to determine the forest areas in order to constrain the possible sites for occurring of avalanches. Although the avalanche can occur on any slope given the right condition, certain locations are naturally more dangerous than others. Existing avalanche sites supplied from Appalachian Mountain Club have been use to determine the accuracy of the results. Predicted Suitable Avalanche Sites Land cover map Forest- non forest map Morphological and terrain factors Vegetation Constraint Methodology Multi - criteria evaluation process has been applied to identify avalanche hazard zones. Three factors have been use : Elevation greater the 650 meters; Slope greater than 25 degrees; 1000 meters from the bed of the gullies; The result has been constraint by : Areas with low vegetation. Two procedures are common for MCE. The first involves the Boolean overlay where all criteria are needed to meet the suitability logic. The second is known as Weighted Linear Combination, where factors are standardized then combined according their weights.The result is a suitability map which is masked by the Boolean constraint. Modules such as PCLASS and FUZZY were used to create suitability maps of slope and elevation. Modules RUNOFF and DISTANCE were used to determine the gullies (areas where the aspect change rapidly) and calculate distance from these areas. RECLASS module was used to determine open area and forest area. All factors and constrains were plugged into the multi-criteria decision wizard. The factors were weighted equally to create suitability sites for avalanches. DEM - Elevation Slope Slope greater than 25 degree Terrain - gullies Distance-runoff 1000 m from the bed of the gullies Elevation greater than 650 m Conclusion The Presidential Range of New Hampshire is an unusual mountain environment in the Eastern United States. It is considered as the most dangerous small mountain range in the world. Although, the range has a greatest concentration of avalanche terrain and severe weather condition, it is a preferable place for winter recreation. Using the MCE decision making procedure incorporated in Idrisi, it is possible to define the risk avalanche areas based on topographic factors and vegetation constraints. Considering the elevation, slope steepness, terrain and vegetation cover, it is possible to update an existing avalanche locations. An avalanche in motion Source: The highest peak is Mt Washington (1916m). While severe winter weather is commonly acknowledged, much less is known about the avalanche terrain. Since 1954, there have been 10 avalanche fatalities as well as many other avalanche accidents in the Presidential Range. Study Area The Presidential Range in the White Mountains of New Hampshire has the greatest concentration of avalanche terrain east of the Rocky Mountains in the United States. Tuckerman Ravine, is famous for its scenery, deep snow, hiking and skiing terrain. Acknowledgments This research has been performed in Idrisi Kilimanjaro with the data from: NH GRANIT Web Site; Appalachian Mountain Club. Known Avalanche areas were used for validating the Predicted Suitable Avalanche sites. The Crosstab module result is shown to the right. An area of 9.5 km 2 from the existing sites was predicted from the MCE module. This is two –thirds of the area of 14.9 km 2 existing avalanche sites.