# Debris-flow simulation index

For each rainfall intensity, ursa will conduct multiple simulations. Ursa will determine the fraction of scenarios inundated in each location in the simulation domain. This fraction is called the *debris-flow simulation index* (Barnhart and others, 2025).

If the debris-flow simulation index is equal to zero, it means that no scenario inundated that location. If it is equal to one, it means that all scenarios inundated that location. Areas with low, but non-zero, debris-flow simulation index values are only inundated by the larger, more mobile debris-flow scenarios.

Practical experience indicates that damaging debris flows and hyperconcentrated flows may occur at any debris-flow simulation index value. Flooding may occur outside of the regions with any debris-flow index value, including 0. 

## References

Barnhart, K. R., Kean, J. W., Lindsay, D. N., and Bilderback, E. L., under revision, Multi-site evaluation of a postfire debris-flow runout forecast method, Earth's Future, ...