Reliability of regional and global climate models to simulate precipitation extremes over India

Extreme precipitation events over India have resulted in loss of human lives and damaged infrastructures, food crops, and lifelines. The inability of climate models to credibly project precipitation extremes in India has not been helpful to longer-term hazards resilience policy. However, there have been claims that finer-resolution and regional climate models may improve projections. The claims are examined as hypotheses by comparing models with observations from 1951-2005. This paper evaluates the reliability of the latest generation of general circulation models (GCMs), Coupled Model Intercomparison Project Phase 5 (CMIP5), specifically a subset of the better performing CMIP5 models (called "BEST-GCM"). The relative value of finer-resolution regional climate models (RCMs) is examined by comparing Coordinated Regional Climate Downscaling Experiment (CORDEX) South Asia RCMs ("CORDEX-RCMs") versus the GCMs used by those RCMs to provide boundary conditions, or the host GCMs ("HOST-GCMs"). Ensemble mean of BEST-GCMs performed better for most of the extreme precipitation indices than the CORDEX-RCMs or their HOST-GCMs. Weaker performance shown by ensemble mean of CORDEX-RCMs is largely associated with their high intermodel variation. The CORDEX-RCMs occasionally exhibited slightly superior skills compared to BEST-GCMs; on the whole RCMs failed to significantly outperform GCMs. Observed trends in the extremes were not adequately captured by any of the model ensembles, while neither the GCMs nor the RCMs were determined to be adequate to inform hydrologic design.