Calculating snow-avalanche return period from tree-ring data

The return period is a key element used for snow-avalanche characterization. To calculate the return period, historical data regarding past snow-avalanche activity are required. In mountain areas where past snow avalanches are poorly documented, dendrogeomorphic approaches constitute a reliable method for the reconstruction of past snow avalanches at the temporal scale of living trees. This paper presents an automated method for calculating the snow-avalanche return period using a digital elevation model and the location of the trees disturbed by every reconstructed snow-avalanche occurrence. Unlike the existing method, the method we propose requires neither the calculation of return period for every sampled tree nor the use of interpolation. This new method is based on the determination of spatial extent for every past snow-avalanche occurrence using the upslope area algorithm. The number of past snow-avalanche occurrences is calculated for every pixel of the path. The chronology length is divided by the number of past snow-avalanche occurrences to obtain the return period. In the present paper, both the proposed method and the existing method are applied to calculate the return period for three confined snow-avalanche paths located in Parâng Mountains, part of the Romanian Carpathians. Results are compared and discussed.