“…As such, the FTLE method may not be suitable for studying the predictability of extreme events. Based on the nonlinear local Lyapunov exponent (NLLE, e.g., Ding and Li, 2007;Ding et al, 2008;Li et al, 2020b)method (e.g., Ding and Li, 2007;Ding et al, 2008;Li et al, 2020a), we recently developed a new method, which is the backward nonlinear local Lyapunov exponent (BNLLE) method (Li et al, 2019;Li et al, 2020a;Li et al, 2021). The BNLLE method takes into account nonlinearity, and can be used to study the predictability of given states and, in particular, extreme states.…”