Comparative Analysis of Modern Reanalysis Products for Climate and Weather Studies: Global and Indian Perspectives

Review Article

Abstract

Reanalysis datasets are essential to modern climate and weather research, providing spatially and temporally consistent reconstructions of atmospheric, land, and ocean conditions. They are produced by assimilating historical observations into numerical weather prediction models using fixed physical parameterizations and data assimilation schemes, creating long-term homogeneous datasets crucial for climate diagnostics, extreme event analysis, and impact assessments. Advances in computing power, satellite observations, and assimilation techniques have enabled the development of high-resolution global and regional reanalysis products. This review presents a comparative evaluation of major global reanalysis datasets, including ERA5, MERRA-2, JRA-55, and NCEP/NCAR, alongside Indian climate datasets such as India Meteorological Department (IMD) gridded observations and regional reanalysis efforts by the Indian Institute of Tropical Meteorology (IITM) and the Ministry of Earth Sciences (MoES). Key features—including spatial and temporal resolution, assimilation frameworks, variable availability, strengths, and limitations—are assessed with emphasis on applications over the Indian subcontinent. The analysis shows that global reanalysis products provide dynamically consistent multi-variable datasets suitable for large-scale circulation studies, climate variability assessment, and boundary condition generation. However, their representation of regional processes, particularly the Indian Summer Monsoon, localized extreme rainfall, and temperature extremes, remains limited. In contrast, Indian gridded and regional datasets better capture monsoon rainfall patterns, surface temperature variability, and extreme events due to dense observational networks and regionally optimized methods. The review highlights the need for careful dataset selection based on research objectives and advocates integrated global–regional reanalysis frameworks to improve weather forecasting, climate resilience planning, and climate change impact assessments in India.