What conditions of birational map does the numerically equivalence preserve?

Question

Let $f:X\dashrightarrow Y$ be a birational map between normal varieties. What conditions of birational map does the numerically equivalence preserve? In other words, I want to know the conditions of $f$ satisfying the following property. If we let $D$ and $D'$ be divsors on $X$ such that $D$ is numerically equivalent to $D'$, then $f_*D$ and $f_*D'$ are numerical equivalence.