Nonlinear recurrence quantification of the monsoon-season heavy rainy-days over northwest Himalaya for the baseline and future periods

摘要

Indian summer monsoon has the characteristics of nonlinear dynamical systems. This study verifies the hypothesis that monsoon-season heavy rainy-day climatology over northwest Himalaya would exhibit certain degree of determinism, and expected to modify in its future state due to warming. Hence, recurrence quantification analysis (RQA) leading to quantification of recurrence rate (RR) and determinism (DET) are used. The monsoon-season heavy rainy-day climatologies are computed by area averaging heavy rainy-day (i.e. any day having rainfall＞35.5 mm) of northwestern Indian Himalaya of Uttarakhand (UK), Himachal Pradesh (HP), and Union Territory of Jammu, Kashmir and Ladakh (JKL). Nonlinear characteristics are identified for a baseline period of 1970-2005 using APHRODITE data, and a bias corrected ensemble data for the future period of 2041-2099 produced using five CORDEX experiments under two warming scenarios, RCP 4.5 and 8.5. The heavy rainy-day climatology during 1970-2005 is having a correlation dimension of 1.5 indicating fractal geometry of the system in phase space. Similarly, occurrences of diagonal lines in the recurrence plots of baseline period over JKL, HP, and UK indicated the system is governed by a nonlinear chaotic attractor. A higher recurrence rate during 1970-2005 over HP (RR = 0.123, DET = 0.83) indicated greater determinism than JKL (RR = 0.119, DET = 0.78) and UK (RR = 0.121, DET = 0.75). Mean prediction time of the nonlinear dynamical trajectories controlling heavy rainy-day climatology of 1970-2005 is noted to be higher over UK. Furthermore, the RQA patterns under warmer climates of RCP 4.5 and 8.5 during 2041 -2099 over UK and JKL indicate gradual reduction in the deterministic structures in the phase space. Therefore, it can be inferred that the nonlinear dynamical system governing the monsoon-season heavy rainy-day climatology is expected to lose determinism over certain regions of northwestern Himalaya under warmer climates of RCP 4.5 and 8.5.