  Many dynamical systems exhibit abrupt transitions or tipping as the control
parameter is varied. In scenarios where the parameter is varied continuously,
the rate of change of control parameter greatly affects the performance of
early warning signals (EWS) for such critical transitions.We study the impact
of variation of the control parameter with a finite rate on the performance of
\textcolor{black}{EWS for critical transitions} in a thermoacoustic system (a
horizontal Rijke tube) exhibiting subcritical Hopf bifurcation. There is a
growing interest in developing early warning signals for tipping in real
systems. Firstly, we explore the efficacy of early warning signals based on
critical slowing down and fractal characteristics. From this study, lag-1
autocorrelation (AC) and Hurst exponent H are found to be good measures to
predict the transition well-before the tipping point. The warning time,
obtained using AC and $H$, reduces with an increase in the rate of change of
the control parameter following an inverse power law relation. Hence, for very
fast rates, the warning time may be too short to perform any control action.
Furthermore, we report the observation of a hyperexponential scaling relation
between the AC and the variance of fluctuations during such dynamic Hopf
bifurcation. We construct a theoretical model for noisy Hopf bifurcation
wherein the control parameter is continuously varied at different rates to
study the effect of rate of change of parameter on EWS. Similar results,
including the hyperexponential scaling, are observed in the model as well.
