Model-based reanalyses attempt to reconstruct past climate and specific historical weather events through an ‘optimal’ merging of past observations and modern NWP via the process of data assimilation (DA). Typically, the reanalysis dataset consists of 3-6hourly snapshots of the Earth System (atmosphere, ocean, land, cryosphere) through time (selected cases to multi-decadal sequences). Unlike observation-only based reanalysis datasets, model-based reanalyses provide complete gridded analyses of observed variables (e.g. winds, temperatures, precipitation, etc.) as well as those not observed (fluxes, 3D cloud, etc.) through the complex, multivariate, dynamically and physically consistent processes represented within modern NWP and DA systems.The regional reanalysis has been produced as part of the Indian Monsoon Data Assimilation and Analysis (IMDAA) project and is the outcome of a collaboration between the Met Office (MO), the National Centre for Medium Range Weather Forecasting (NCMRWF) and the India Meteorological Department(IMD).