Creating Higher Resolution Surface Forcings from NLDAS-2/Stage-IV/GSIP for Hydrologic Monitoring

Following recent progresses in areas such as weather forecast/reanalysis, remote sensing, and land surface modeling, researchers have been able to perform real-time or near real-time hydrologic monitoring at an increasingly higher spatial resolution. Currently, the National Center for Environmental Predictions (NCEP) North-American Land Data Assimilation System phase 2 (NLDAS-2) project is providing high-quality operational surface meteorological forcing data products at 0.125 degree resolution. The NLDAS-2 product has been the standard data source for (and backbone of) many current hydrologic monitoring efforts. And higher resolution goals have been set for various ongoing efforts like the 0.3125 degree NLDAS-3.

Here we experiment a way to provide higher resolution surface forcing dataset by downscaling the 0.125 degree NLDAS-2 product and merging it with the 4-km Stage-IV radar/gauge rainfall product and the GOES Solar Insolation Product (GSIP). The hourly Stage-IV product is first gap-filled with Stage II product and then adjusted against 6-hourly Stage IV data. The adjusted 4-km Stage-IV is then rescaled to match NLDAS-2 precpitation at 0.125 degree and daily level (preserving variability at fine temporal/spatial scales). The GSIP is used replace NLDAS-2 solar radiation whenever available. Other NLDAS-2 variables are downscaled with the help of 1-km elevation data: 1) elevation adjustment for temperature (fixed lapse rate) and pressure (hydrostatic), 2) bilinear interpolation of relative humidity & vapor pressure calculated from relative humidity and elevation adjusted temperature/pressure, 3) longwave from elevation adjusted radiative temperature, 4) solar angle adjustment for GSIP, 5) bilinear interpolation of wind & shortwave radiation.

We also show how the downscaled forcing dataset helps enable a near real-time hydrologic monitoring system over the Contiguous United States (CONUS).