CHyM Alarm Index
It is an improvement of CAI1 (see Tomassetti et al., 2005) used for years in the operational activities for Central Italy carried out with CHyM model. CAI2 is calculated for each elementary cell, i, of the simulated domain at time t as follow:

where P is the precipitation field, t the time and s the space variable. In the previous formula, the space integral is carried out over the whole upstream basin of cell i, while the time integral is carried out between t-Δt and t, being Δt the average runoff time for the upstream basin; the runoff time is usually defined as an average time that a drop of rain will take to runoff toward the cell i. The CAI2 index also has a simple physical interpretation: it is the ratio between the total rain drained by a cell and the total area drained by the same cell, namely it represent the average precipitation drained by a cell during a time interval corresponding to the runoff time.
Best Discharge-based Drainage alarm index

Namely the ratio between maximum value of the discharge Q_i during the simulation and the hydraulic radius, R of the considered grid point i. According to many other authors the hydraulic radius can be computed as a function of drained area.
HTML code automatically generated using "IDRA2Web" software version 1.0 developped by Cetemps Hydrology Group This document has been updated on May 2, 2013 h: 11:41