Overview of the North American Land Data Assimilation System

The NCEP Environmental Modeling Center and its NOAA Climate Program Office/Climate Prediction Program for the Americas (CPO/CPPA) partners developed the North American Land Data Assimilation System (NLDAS) to monitor land surface states, and surface water and energy budgets. NLDAS is used to support the NCEP/Climate Prediction Center and the National Integrated Drought Information System in drought and flood monitoring and seasonal hydrological forecasting.

NLDAS land-surface monitoring consists of a 29-year (1979-2007) retrospective and a companion near real-time extension, with hourly water and energy fluxes and state variables (e.g. soil moisture, snowpack, runoff, evaporation) at 1/8th degree resolution over the continental US from four land surface models (NCEP/Noah, NASA/Mosaic, OHD/SAC, and Princeton/VIC). Land model forcing is from the NCEP retrospective and real-time North American Regional Reanalysis System (NARR), except precipitation which uses daily gauge-based precipitation disaggregated to hourly using radar and satellite data.

The NLDAS seasonal hydrological prediction system uses three different sources for generating downscaled ensemble seasonal forecasts of surface forcing to drive the VIC land model in an uncoupled mode which yields one to six month ensemble seasonal hydrological predictions (of e.g. streamflow, etc).

Long-term NLDAS water fluxes (streamflow, evaporation), energy fluxes (sensible heat, latent heat, ground heat, net radiation) and state variables (soil moisture, soil temperature, snow cover, snow water equivalent) are evaluated and validated using in-situ observations and retrieved products from satellite data.