Retrospective and Near–Real-Time Surface Meteorology in the North American Land Data Assimilation System Phase 3 (NLDAS-3)

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Abstract High-resolution, reliable surface meteorological estimates are essential for hydrologic modeling, climate research, and disaster management. Previous phases of the North American Land Data Assimilation System (NLDAS-1 and NLDAS-2), developed jointly by NOAA, NASA, and academic partners, established widely used observation-driven land hydrology modeling environments over the contiguous United States, supporting applications such as drought monitoring, water resource management, agricultural planning, and land–atmosphere research. However, increasing scientific and operational demands require finer spatial resolution, broader geographic coverage, and near-real-time availability. Building on this foundation, we present the North American Land Data Assimilation System Phase 3 (NLDAS-3), which expands coverage to all of North and Central America and increases spatial resolution to 1 km. We developed a 1-km, hourly gridded surface meteorological dataset available in both retrospective and near-real-time modes. NLDAS-3 integrates satellite-based precipitation products and reanalysis fields from NASA and partner agencies. Meteorological variables are downscaled using elevation-based corrections to better represent fine-scale spatial variability across complex terrain. Evaluation against more than 3,000 ground stations and ten widely used reference datasets demonstrates that NLDAS-3 consistently outperforms existing products. Relative to NLDAS-2, NLDAS-3 achieves substantial average reductions in root mean square error (RMSE), including 18% for precipitation, 10% for air temperature, 42% for surface pressure, and 22% for longwave radiation. Extended Triple Collocation analysis further corroborates these improvements. Overall, NLDAS-3 represents a significant advancement in the quality, consistency, availability, and spatial resolution of surface meteorological data, providing a valuable resource for research and operational applications across North and Central America.

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