Benchmarking the next phase of the North American Land Data Assimilation System (NLDAS) using the Land Verification Toolkit (LVT)

The North American Land Data Assimilation System (NLDAS) has produced over 35 years (Jan 1979 to present) of hourly land-surface meteorology and surface states, including soil moistures and temperatures, snow cover, runoff, and evapotranspiration. NLDAS uses the best-available observations and reanalyses to create near-surface forcing for land-surface models (LSMs) in “off-line” mode. The surface forcing is then used to drive the LSMs to produce long-term consistent LSM output datasets. The NLDAS domain extends over North America from 25-53North on a 1/8th-degree grid. NLDAS datasets are available at NCEP/EMC and via the GES DISC at NASA/GSFC. Datasets are updated in near real-time (with a typical 4-day lag) and a Drought Monitor is produced using the LSM output, including an ensemble-mean. NLDAS is a collaboration project between NCEP/EMC, NASA/GSFC, Princeton University, the University of Washington, NWS/OHD, and NCEP/CPC.

The existing Phase 2 of NLDAS employed four unique LSMs, each driven separately by the surface forcing. The four LSMs are: EMC's Noah version 2.8, GSFC's Mosaic, Princeton's VIC version 4.0.3, and OHD's SAC/SNOW-17. In the years since these model versions were first put into use for NLDAS, they have each received significant upgrades via improved model physics as well as parameter modifications. For the next phase of NLDAS, GSFC's Catchment LSM (the land model within the GEOS-5 GCM) has replaced the Mosaic LSM – and the Noah, VIC, and SAC-HTET/SNOW-17 LSMs were brought into their latest model versions. These models are run using the Land Information System (LIS) software framework developed at GSFC. The LIS software allows a common driver for all LSMs as well as the assimilation of remotely-sensed soil moisture and snow to improve model states and fluxes.

For this presentation, the new and upgraded LSMs will be evaluated against the Phase 2 versions of the LSMs as well as against available observations, both gridded and in situ. The Land Verification Toolkit (LVT), also developed at GSFC, will be used to compare the performances of the various LSMs and model versions. An integrated benchmarking system for NLDAS will be presented that demonstrates strengths and weaknesses of the land models through comparisons of energy and water cycle budgets as well as their individual terms. The goal of this system is to document the changes from NLDAS-2 to the next phase of NLDAS as well as to help identify the land model output that may be best to select for each end user's particular application.