  Let $\{g_t\}_{t\in [0,T)}$ be a family of complete time-depending Riemannian
matrics on a manifold which evolves under backwards Ricci flow. The It\^{o}
formula is established for the $\mathcal{L}$-distance of the $g_t$-Brownian
motion to a fixed reference point ($\mathcal{L}$-base). Furthermore, as an
application, we construct a coupling by parallel displacement which yields a
new proof of some results of Topping.
