In this paper, we perform a societal and economic risk assessment
for debris flows at the regional scale, for lower Valtellina, Northern
Italy. We apply a simple empirical debris-flow model, FLOW-R, which
couples a probabilistic flow routing algorithm with an energy line
approach, providing the relative probability of transit, and the
maximum kinetic energy, for each cell. By assessing a vulnerability
to people and to other exposed elements (buildings, public facilities,
crops, woods, communication lines), and their economic value, we
calculated the expected annual losses both in terms of lives (societal
risk) and goods (direct economic risk). For societal risk assessment,
we distinguish for the day and night scenarios. The distribution
of people at different moments of the day was considered, accounting
for the occupational and recreational activities, to provide a more
realistic assessment of risk. Market studies were performed in order
to assess a realistic economic value to goods, structures, and lifelines.
As terrain unit, a 20 m x 20 m cell was used, in accordance with
data availability and the spatial resolution requested for a risk
assessment at this scale. Societal risk the whole area amounts to
1.98 and 4.22 deaths/year for the day and the night scenarios, respectively,
with a maximum of 0.013 deaths/year/cell. Economic risk for goods
amounts to 1,760,291 ?/year, with a maximum of 13,814 ?/year/cell.