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 $7%$.
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