Climate change impacts on tropical cyclones of the Arabian Sea: Projections and uncertainty investigations

Abstract

This study investigates some of the uncertainties sources associated with the pseudo global warming (PGW) approach which was employed to project future patterns of tropical cyclones (TCs) over the Arabian Sea (AS). First, the climate variables controlling the patterns of tropical cyclones were extracted from reanalysis datasets of ERA5, ERAI, CFSR, and NCEP/NCAR. Then, each dataset was evaluated against long‐term measurements to identify the best‐performing reanalysis dataset. ERA5 showed the best performance for most of the variables. Outputs of 20 CMIP5 global climate models (GCMs) were then evaluated against the ERA5 data resulting in an ensemble of the best performing GCMs. A PGW framework was then used to project the changes in patterns of three significant historical cyclones: Gonu, Phet, and Ashobaa. In doing so, the signals of future climate variables were extracted from the GCMs ensemble to modify the initial and boundary conditions of the WRF model which was previously tuned for reproducing the historical TCs. Different tests were conducted to address the sources of uncertainty in the PGW approach, including the selection of the climate variables contributing to the computation of the signals, the selection of GCMs, and the spatial variation of signals. A considerable sensitivity of the projected track and intensity of TCs to the choice of GCMs was observed, acknowledging the importance of GCMs evaluation before calculating the signals. Moreover, it was found that among all variables, signals of sea surface temperature and air temperature have major effects on the cyclone's track and intensity. Apart from that, when the signals were applied to the domain of the WRF model uniformly, compared to applying spatially varying signals, different tracks and intensities for future TCs were also observed. Overall, the findings of this paper challenge the reliability of the projected changes in TCs patterns obtained from PGW.

CycloneShaheen: the exceptional tropical cyclone of October 2021 in the Gulf of Oman

“…Future regional climate projections using downscaled Global Climate Models (GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5), suggest increased intensity and frequency of cyclones in the Arabian Sea (Bell et al ., 2020; Ranji et al ., 2022). An increase in ASB cyclone genesis frequency is consistent with changes in vertical wind shear and RH (Bell et al ., 2020).…”

“…Recent modelling and cyclone reanalysis by Ranji et al . (2022) used an ensemble of downscaled GCMs to show that three historically significant storms in the northern Arabian Sea ( Gonu , Phet and Ashobaa ) would increase in intensity under future RCP4.5 and RCP8.5 emissions scenarios. Emanuel (2021) estimated global cyclone activity using the latest CIMP6 models: the results largely agreed with previous CIMP5 experiments, showing an increase in both the frequency and severity of cyclones in response to increasing greenhouse gas concentrations in the Northern Hemisphere in general, with a westward expansion of the cyclogenesis region in the Arabian Sea.…”

Uncertainties in the Projected Patterns of Wave-Driven Longshore Sediment Transport Along a Non-straight Coastline

“…These biases can also increase the uncertainty of GCM-Ws projections (Morim et al, 2018). To address this issue, bias correction (BC) methods have been employed so far to correct the systematic errors of GCMs outputs (e.g., Ranji et al, 2022) or even GCM-Ws (Lemos et al, 2020a,b). BC methods try to enhance the agreement between model simulations and observational/reference data for a historical time scale (baseline period).…”

Waves and Storm Surges of Tropical Cyclones Over the Arabian Sea: Future Projections and Uncertainty Analysis

“…The uncertainty analysis, which requires a large ensemble set, is thus necessary to estimate future TCs and their subsequences such as giant waves and surges (Mori et al, 2021). Following Ranji et al (2022), this study aims to estimate the changes of TC generated waves and surge heights, in a changing climate of the Arabian Sea, together with addressing the uncertainties associated with numerical models to estimate their changes.…”