  We discuss rapidity decorrelation caused by hydrodynamic fluctuations in
high-energy nuclear collisions at the LHC energy. We employ an integrated
dynamical model which is a combination of the Monte Carlo version of Glauber
model with extension to longitudinal direction for initial conditions, full
three-dimensional relativistic fluctuating hydrodynamics for the space-time
evolution of created matter in the intermediate stage and a hadronic cascade
model in the late stage. We switch on and off the hydrodynamic fluctuations in
the hydrodynamic stage to understand the effects of hydrodynamic fluctuations
on factorisation ratios $r_{n}(\eta^a_p, \eta^b_p)$. To understand the rapidity
gap dependence of the factorisation ratio comprehensively, we analyse Legendre
coefficients $A^k_2$ and $B^k_2$.
