Impact of the CMIP6 Model Resolution on the Future Behaviour of Wind-Driven Wave Climate for the North Indian Ocean

We investigate the past and future variations in wind-driven wave climate over the North Indian Ocean (NIO) region utilising three climate models involved in the High-Resolution Model Intercomparison Project (HighResMIP) within the Coupled Model Intercomparison Project Phase 6 (CMIP6). We analyse the impact of horizontal grid resolution on the accuracy of reproducing past and future changes in wave climate. Wave climate simulated by Global Climate Model (GCM)-forced Wave Watch III (WWIII) simulation outputs from the historical (hist-1950) and future (highres-future) experiments are employed to depict the multi-resolution portrayal of wave climate and to assess any systematic differences arising from resolution enhancements. Compared with ERA5, the GCM with 50 km resolution simulates stronger waves. The pattern of underestimation and overestimation from ERA5 becomes more pronounced in both extent and magnitude as the GCM resolution decreases to 100 km and 250 km. These coarse-resolution models also exhibit deficiencies in representing inter-annual and inter-seasonal variability, particularly in regions impacted by Tropical Cyclones (TCs) such as the Southeastern Bay of Bengal (BoB), Andaman Sea, Southeastern Arabian Sea (AS), offshore of Western India and so forth. This study highlights the critical issue of relying on climate model data without adequately considering their coarse resolutions or inherent biases compared to observational data. In contrast to the historical wave climate, future projections suggest a decrease in 50-year return values (RV50) over the eastern regions and an increase in the western regions of the AS. Specifically, a 1-m rise in RV50 is projected for the Northwestern AS regions. According to the 50 km model simulation, significant changes in annual mean and maximum Significant Wave Height (SWH) and wind speed are observed in the Eastern AS and Southern BoB, where maximum wave heights are projected to decrease. In contrast, increased wave activity is anticipated in the future for the Northwestern AS and Western AS.