Table 2 Interpretation of indicators’ values by risk grade

\({I}^{r}\)(\({\mathrm{IR}}^{\mathrm{r}}\)) ≤ 0.25

Catastrophic risk zone

0.25 < \({I}^{r}\) (\({\mathrm{IR}}^{r}\)) ≤ 0.5

Critical risk zone

0.5 < \({I}^{r}\) (\({\mathrm{IR}}^{r}\)) ≤ 0.75

Significant risk zone

0.75 < \({I}^{r}\) (\({\mathrm{IR}}^{r}\)) ≤ 1

Moderate risk zone

\({I}^{r}\)(\({\mathrm{IR}}^{r}\)) > 1

Stability zone