  T2HK and T2HKK are the proposed extensions of the of T2K experiments in Japan
and DUNE is the future long-baseline program of Fermilab. All these three
experiments will use extremely high beam power and large detector volumes to
observe neutrino oscillation. Because of the large statistics, these
experiments will be highly sensitive to systematics. Thus a small change in the
systematics can cause a significant change in their sensitivities. To
understand this, we do a comparative study of T2HK, T2HKK and DUNE with respect
to their systematic errors. Specifically we study the effect of the systematics
in the determination of neutrino mass hierarchy, octant of the mixing angle
$\theta_{23}$ and $\delta_{CP}$ in the standard three flavor scenario and also
analyze the role of systematic uncertainties in constraining the parameters of
the nonstandard interactions in neutrino propagation. Taking the overall
systematics for signal and background normalization, we quantify how the
sensitivities of these experiments change if the systematics are varied from
$1\%$ to $7\%$.
