North American Land Data Assimilation System Version 2.5: Real-Time Evaluation and Operational Implementation at NCEP

The North American Land Data Assimilation System (NLDAS) has a long successful history of producing A) surface meteorological forcing, and B) land surface datasets from land-surface models (LSMs) to provide soil moisture, snow cover, surface evaporation, runoff/streamflow products, among other quantities. Since Phase 2 of NLDAS (NLDAS-2) was implemented in the NCEP product suite in August 2014, these products have been widely used for drought monitoring and water resources management purposes. However, this operational system has a 3.5-4 day time lag, which hampers its applications for real-time operational tasks, such as the weekly US drought monitor and initializing land states in NWP models. To close this time lag, the NCEP/EMC NLDAS team worked with its collaborators for the last two years to integrate CPC daily gauge precipitation, EMC hourly stage IV radar-based national precipitation analyses, and fields from both the NAMv4 reanalysis and forecast to upgrade the current operational NLDAS system to an actual real-time NLDAS system with zero time lag. The upgraded NLDAS-2.5 will be implemented in October 2018. The resulting zero-lag, real-time status of NLDAS-2.5 products will positively benefit the NLDAS Drought Monitor, which is updated daily in support of national operational drought monitoring and prediction tasks. Real-time NLDAS-2.5 drought products will result in better timeliness for depictions of drought extent and severity over CONUS.

This presentation summarizes the evaluation of the upgraded fully real-time NLDAS-2.5 system including its design and infrastructure changes from NLDAS-2, product distribution, and assessment of water and energy fluxes, and state variables, as well as its impacts when compared with NLDAS-2 drought persistence results. In particular, using the current operational NLDAS drought-monitor indicators as a benchmark, we evaluate the impact of real-time surface meteorological forcing, including NAMv4 forecast products, on drought indicators.