35. Assimilation of High Resolution MODIS Snow Cover Data into
the LIS Noah and SAC-HT/SNOW17 Models over the Continental
United States (CONUS)
Author：
Jiarui DONG (NOAA/NCEP/EMC & IMSG), Mike EK (NOAA/NCEP/EMC)
Affiliation： NOAA/NCEP/EMC
In the western United States, over half of the water supply is derived from mountain
snowmelt. In many mid latitude and high altitude regions, the snow delays runoff
and provides water in the spring and summer when it is needed most. Therefore,
accurate knowledge of snowpack properties is important for short-term weather
forecasts, climate change prediction, and hydrologic forecasting.
As both the model predictions and passive microwave snow water equivalent (SWE)
observations contain large errors due to land surface complexities and temporally
frequent snowmelt processes in the western United States, the 500-m daily MODIS
snow cover area (SCA) product has been used in this study as an important
constraint on snowpack processes in land surface and hydrological models. The
uncertainty in the MODIS SCA product has been assessed over some selected
regions, and quality control will be applied to the MODIS SCA product before it is
assimilated into the SNOW17 model.
In this study, we assimilate the MODIS derived snow cover fraction (SCF) into the
LIS Noah land surface and SAC-HT/SNOW17 hydrological models operating on the
HRAP (Hydrologic Rainfall Analysis Project) grid at 4.7625-km resolution over the
test regions and potential over the entire CONUS. To avoid cloud contamination, we
update the snow cover fraction at pixels which feature less than 50% cloud coverage.
Because the change in snow cover fraction makes no change to the amount of SWE
in the SNOW17 module, we have developed a new scheme to account for the effect
of a change in snow cover fraction to total SWE. We select the traditional bisection
method to study this inverse problem, and perform a series of tests to assess the
assimilation algorithm performance. Multi-year model simulations with and without
MODIS SCF assimilation are presented, and evaluated with in-situ SWE
observations and stream flow records.