Progress of the NOAA/NCEP NLDAS Drought Monitor and NLDAS Products

The NCEP Environmental Modeling Center (EMC) collaborated with its CPPA (Climate Prediction Program of the Americas) partners to develop a North American Land Data Assimilation System (NLDAS, http://www.emc.ncep.noaa.gov/mmb/nldas). The NLDAS system includes multi-model analysis/monitoring products to focus on drought and flood monitoring. NLDAS products consist of 29-year (1979-2007) retrospective and 1.5-year near realtime (2008-current time with a 4-day lag) water and energy fluxes, and state variables with an hourly temporal resolution and a 1/8th degree spatial resolution for four land surface models (NCEP/Noah, NASA/Mosaic, OHD/SAC, and Princeton/VIC). This study used commonly hourly land surface forcing derived from NCEP's retrospective and realtime North American Regional Reanalysis System (NARR) except for precipitation. The precipitation forcing is anchored to a daily gauge-only precipitation analysis over CONUS that applies the Parameter-elevation Regressions on Independent Slopes Model (PRISM) correction. This daily precipitation analysis is then temporally disaggregated to hourly precipitation amounts using stage II radar and satellite retrieved precipitation products. The NARR-based surface downward solar radiation is bias-corrected using seven years (1997-2004) of GOES satellite-derived solar radiation retrievals.

The 29-year NLDAS retrospective is used to derive the climatology of each of the four land models. Then current realtime land states (soil moisture, snowpack) and water fluxes (evaporation, total runoff, routing streamflow) of each of the four land models from daily update executions are depicted as anomalies and percentiles with respect to their own model climatology. One key application of the realtime updates is drought monitoring over CONUS, shown at the "NLDAS Drought" tab of the NLDAS web site.

This presentation summarizes the upgrade of three land surface models (i.e., Noah, SAC, VIC) and their rerun results. We compare the results between rerun and old-run and validated them using USGS observed streamflow at 965 basins over the CONUS. We also compare the results from NLDAS drought monitoring and US drought monitor for the last year. Finally we discussed NLDAS drought monitoring and its products expansion to CPC and National Integrated Drought Information System (NIDIS).