mrstu / ulm

Unified Land Model

Release Notes - Unified Land Model (ULM)

The Unified Land Model (ULM) is an implementation of the Noah Land Surface Model and the Sacramento hydrologic model.

Important features include:

• NetCDF formatted and ALMA convention output
• The ability to characterize sub grid cell elevation heterogeneity via elevation bands

##Date: 2015-Mar-11

Authors:

• Ben Livneh, [email protected]
• Ted Bohn, [email protected]
• (PI: Dennis Lettenmaier)

Contributors

• Matt Stumbaugh, [email protected]
• (Bart Nijssen)

Source

Land Surface Hydrology Group Department of Civil and Environmental Engineering University of Washington, Seattle, USA

History

• 2013-Mar-11
  • Bug fixes
  • snow scraping option
  • check for snowband elevation and elevation parameter consistency
  • Conversion of CHANGELOG and README from *.txt to *.md
• 2012-Jul-23 Updated ULM updates and runfiles BL
• 2008-May-12 Modified to reflect NOAH 2.8 update. TJB

Notes

Compiling ULM

The makefile in this directory is set up to compile ULM on hydra.

• subdaily forcings in netCDF fomat must include: downwelling sw, lw radiations, specific humidity, surface pressure, rainfall and snowfall rates, air temperature, and wind.
• There is a sample global file in this directory "ulm.input.template" where the strings that begin and end with "X" are those paths to be replaced.
• Input data are the same as Noah + SAC with the exception of the "sac_const.txt" file. This file is different for ULM than for SAC. Please use the file in this directory as the constants file for all basins: sac_const.txt
• In order to change which variables are output, please change the files: driver/OPEN_OUTPUT.f90 and driver/WRITE_OUTPUT.f90 and ensure that the variable list match in both of these files.
• To run ULM, simply type the name of the executable followed by the global file e.g. % ulm ulm.input

Further Details

The original base version of the model physics source code (the SFLX routine, found in the "src/physics" directory) was Noah 2.7.1.As NOAA/NCEP have updated their version of SFLX, we have attempted to incorporate their latest updates into our code base, keeping our version almost identical to theirs. The current version of SFLX in our implementation is 2.8.

The bulk of the changes to the code were made in the i/o and pre-processing code, found in the "src/driver" directory.The i/o and preproc code began from the NLDAS driver code; since then we have changed the files from fortran 77 to fortran 90 to take advantage of dynamic array allocation (which allows us to run the model over any arbitrary basin simply by feeding it new parameter files, without needing to recompile the code with new array dimensions).

The implementation of elevation bands involves dividing the grid cell into fractions ("bands"), representing quantiles of the cell's elevation distribution.Each band's temperature and precipitation are derived from the grid cell average temperature and precipitation based on parameters from the snowbands parameter file.Each band's values of DQSDT2, TH2, SPFH_SAT, and SPFH are modified accordingly, while the values of the other forcing variables are held equal to the grid cell average values. In addition, the following state variables have an added "band" dimension:

• T1
• STC
• SMC
• SH2O
• CMC
• SNOWH
• SNEQV
• SNCOVR
• LSTSNW

The following derived quantities also have an added "band" dimension:

• CH
• CM
• ALB_TOT (albedo)
• SOLNET(net solar radiation)

The outputs of the SFLX routine are aggregated over all elevation bands to give average values for the entire grid cell.

One of the other models in our system here is the SAC/SNOW17 model, which needs potential evapotranspiration supplied as an input.The value output by Noah is typically the used as the input to SAC/SNOW17.Since this quantity is band- dependent, and also must be available at the same time intervals as the forcing data, we have modified Noah to output a separate PE file, containing PE as a function of grid cell and band, at the time interval of the forcing data.

The driver code is set up to save a state (restart) file and end the simulation when the end of the forcing file is reached.This state file can be used as the initial condition file for a new run using the next forcing file.

To compile the noah model, you may first need to edit src/makefile so that the compiler is set to your system's fortran 90 (or later) compiler.In addition, you will need to have netCDF libraries installed on your system.Then, simply cd to the "src" directory and type "make".You may then wish to copy the executable "noah" to the "bin" directory (this insulates your working version of noah from any development you might do in the "src" directory).

To run the noah model, first prepare a control file listing the names of the necessary input files and the values of the run parameters (sample input files and documentation should be available under the "data" directory in this distribution).If your current directory is the "bin" directory, and your control file is located at /my_path/input.txt, simply type noah /my_path/input.txt to run the model.To create a log file, redirect the model's output from stdout to a file:

noah /my_path/input.txt > logfile.txt