Assessing Added Value of Dynamical Downscaling for Wind Speed Over South Asia: A Distribution Added Value Approach
摘要
High-resolution regional climate model simulations have become increasingly prevalent due to advances in computational resources. In this study, we examine the added value of wind speed simulations of two regional climate models (RCA4, REMO2009) forced by MPI’s Earth System Model (MPI-ESM-LR) over South Asia. The simulation data is acquired from the Coordinated Regional Climate Downscaling Experiment (CORDEX-SA) for the period from 1974 to 2004. To quantify the added value, we adopt the recently developed Distribution Added Value (DAV) metric, which allows a direct comparison of probability density functions (PDFs) for wind speed between the high-resolution regional model runs and the HadISD observational data. We calculate the DAV for both full PDFs and the upper-tail PDFs (P95) at the annual and seasonal levels (autumn, spring, summer, and winter). For the RCA4 model, our analysis reveals substantial added value, with DAV values ranging from 8.4 to 11.5% for the full PDF and from 4.7 to 12.1% for the upper-tail PDF (P95). Conversely, the REMO2009 model shows negative DAV values, indicating limited improvement in reproducing wind speed patterns, with values ranging from −9.9 to −10.8% for the full PDF and from −13.5 to −17.9% for the upper-tail PDF (P95). The ensemble mean shows DAV values from −2.4 to −2.1% for the full PDF and from 0.6 to 1.8% for the upper-tail PDF (P95). Our findings indicate that the RCA4 model demonstrates significant added value in reproducing wind speed characteristics over South Asia, particularly in extreme events. On the other hand, the REMO2009 model reveals limited improvement in capturing wind speed patterns, while the ensemble mean exhibits moderate added value. Overall, our study highlights the advantages of utilizing high-resolution wind speed downscaling, as demonstrated by the positive DAV values in RCA4, offering valuable insights for climate modeling and impact assessments in South Asia.