Evaluation of New and Upgraded Land-Surface Models in the North American Land Data Assimilation System (NLDAS)

The North American Land Data Assimilation System (NLDAS) has produced over 34 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 a long-term consistent LSM output dataset. The NLDAS domain extends from 25 to 53 North 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 have been 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. The results of the data assimilation will be presented in a companion presentation submitted to this same session.

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. The Land surface Verification Toolkit (LVT), also developed at GSFC, will be used to compare the performances of the various LSMs and model versions. Evaluations against gridded and in situ observations of surface fluxes, snow, and soil moisture will be shown, also including routed model runoff against streamflow observations. Model climatologies and time series over the entire NLDAS record will also be presented, as well as comparisons of various energy and water cycle budget terms.