ARF (Areal Reduction Factor)¶

HDAT optionally applies ARF to rainfall depth/intensity for larger catchments.

Trigger¶

ARF is applied if enabled and:

\[ area_{km^2} \ge area_{ref} \]

\[ ARF = 1 - 0.044 \cdot area_{km^2}^{0.275} \]

Clamp:

\[ ARF \ge 0.6 \]

Adjusted rainfall depth:

\[ P_{adj} = P \cdot ARF \]

ARF governance is regional; treat this as the legacy behavior to preserve, and document if a project requires a different authority formula.
Always record whether ARF was applied, the computed ARF value, and the area used for evaluation.