Structure for Unifying Multiple Modeling Alternatives:
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This is the source code repository for the Structure for Unifying Multiple Modeling Alternatives or SUMMA. More information about SUMMA, including publications, test data sets, and sample applications can be found on the SUMMA web site at NCAR.

##Description SUMMA is a hydrologic modeling aproach that is built on a common set of conservation equations and a common numerical solver, which together constitute the “structural core” of the model. Different modeling approaches can then be implemented within the structural core, enabling a controlled and systematic analysis of alternative modeling options, and providing insight for future model development.

The important modeling features are:

  1. The formulation of the conservation model equations is cleanly separated from their numerical solution;

  2. Different model representations of physical processes (in particular, different flux parameterizations) can be used within a common set of conservation equations; and

  3. The physical processes can be organized in different spatial configurations, including model elements of different shape and connectivity (e.g., nested multi-scale grids and HRUs).

SUMMA can be used to configure a wide range of hydrological model alternatives. We anticipate that systematic model analysis will help researchers and practitioners understand reasons for inter-model differences in model behavior, and, when applied across a large sample of catchments, may provide insights on the dominance of different physical processes and regional variability in the suitability of different modeling approaches. An important application of SUMMA is selecting specific physics options to reproduce the behavior of existing models – these applications of “model mimicry” can be used to define reference (benchmark) cases in structured model comparison experiments, and can help diagnose weaknesses of individual models in different hydroclimatic regimes.

##Credits SUMMA's initial implementation is described in two papers published in Water Resources Research. If you use SUMMA, please credit these two publications.

  • Martyn P. Clark, Bart Nijssen, Jessica D. Lundquist, Dmitri Kavetski, David E. Rupp, Ross A. Woods, Jim E. Freer, Ethan D. Gutmann, Andrew W. Wood, Levi D. Brekke, Jeffrey R. Arnold, David J. Gochis, Roy M. Rasmussen, 2015: A unified approach for process-based hydrologic modeling. Part 1: Modeling concept. Water Resources Research, doi:10.1002/2015WR017198.

  • Martyn P. Clark, Bart Nijssen, Jessica D. Lundquist, Dmitri Kavetski, David E. Rupp, Ross A. Woods, Jim E. Freer, Ethan D. Gutmann, Andrew W. Wood, David J. Gochis, Roy M. Rasmussen, David G. Tarboton, Vinod Mahat, Gerald N. Flerchinger, Danny G. Marks, 2015: A unified approach for process-based hydrologic modeling: Part 2. Model implementation and example applications. Water Resources Research, doi:10.1002/2015WR017200.

In addition, an NCAR technical note describes the SUMMA implementation in detail:

  • Martyn P. Clark, Bart Nijssen, Jessica D. Lundquist, Dmitri Kavetski, David E. Rupp, Ross A. Woods, Jim E. Freer, Ethan D. Gutmann, Andy W. Wood, Levi D. Brekke, Jeffrey R. Arnold, David J. Gochis, Roy M. Rasmussen, David G. Tarboton, Vinod Mahat, Gerald N. Flerchinger, and Danny G. Marks, 2015: The structure for unifying multiple modeling alternatives (SUMMA), Version 1.0: Technical Description. NCAR Technical Note NCAR/TN-514+STR, 50 pp., doi:10.5065/D6WQ01TD.


We have successfully installed SUMMA on a number of Unix-like (*nix) operating systems, including Linux and Darwin (Mac OS X). To compile SUMMA, you will need:

  • a Fortran compiler. We have successfully used the intel Fortran compiler (ifort) and the GNU Fortran compiler (gfortran, version 4.8 or higher), the latter of which is freely available. Since we do not use any compiler-specific extensions, you should be able to compile SUMMA with other Fortran compilers as well.

    If you do not have a Fortran compiler, you can install gfortran for free. The easiest way is to use a package manager. Which package manager depends on your *nix flavor. On OS X, you can use any of the free OS X package managers, including MacPorts, fink, or homebrew. Note that gfortran is installed as part of the gcc compiler suite.

  • the NetCDF libraries. NetCDF or the Network Common Data Format is a set of software libraries and self-describing, machine-independent data formats that support the creation, access, and sharing of array-oriented scientific data. They are widely used in the hydrometeorological community and eventually all SUMMA I/O will use NetCDF. Most *nix package managers include a NetCDF port. Note that you need to ensure that:

    • You have NetCDF version 4.x;
    • The NetCDF libraries are compiled with the same compiler as you plan to use for compiling SUMMA; and
    • You have the NetCDF Fortran library installed (libnetcdff.*) and not just the C-version.
  • the LAPACK — Linear Algebra PACKage library. LAPACK provides a series of routines for linear algebra operations, including matrix solvers. How to install the library depends on your *nix variant and is not covered here. For example, on OS X you will get all the necessary LAPACK routines by installing the ATLAS software (again, this is easiest using a package manager; note that ATLAS can take many hours to build the first time when you install it).

  • The ATLAS (Automatically Tuned Linear Algebra Software) library. Note that this is required on OS X using the gfortran compiler to be able to use LAPACK. It's not clear that this is used on other *nix machines.

  • a copy of the SUMMA source code from this repo. You have a number of options:

    • If you just want to use the latest stable release of SUMMA, then simply look for the most recent tag;
    • If you want the latest and greatest (and potentially erroneous), download a copy of the master branch (or clone it);
    • If you may want to do SUMMA development, then fork the repo on github and start editing your own copy.

    Note that you will not be able to contribute to the main SUMMA repo directly. If you are seriously interested in contributing, spend a little time learning git. It will be useful anyway. For more information about working with the SUMMA code, please see the following documents:

Once you have all the above, you can compile SUMMA using the following steps:

  1. Navigate to your local copy of the SUMMA directory and go to the build subdirectory;

  2. Edit part 0 of the Makefile. At the very least, you will need to set F_MASTER and FC. You may also need to set NCDF_PATH and LAPK_PATH and you may need to add some extra entries if you are using a different Fortran compiler or your setup is different (if someone wants to contribute an actual configure script that would be great);

  3. Type make. If all goes well, this will build SUMMA and move the executable summa.exe to the bin directory. You may get some warnings (depending on your compiler settings), but you should not get any errors;

  4. Pay attention to the make output. You may need to set some environment variables (LD_LIBRARY_PATH in particular) to support dynamic linking;

  5. Run summa.exe. If all goes well, you should get an error message that looks something like:

    Usage: summa.exe master_file [-s file_suffix] [-g startGRU countGRU] [-c checkHRU]
      summa.exe   -- summa executable
      file_suffix -- text string defining the output file suffix
      master_file -- path/name of master file
      startGRU    -- the index of the first GRU for a parallelization run
      countGRU    -- the number of GRUs for a parallelization run
      checkHRU    -- the index of the HRU for a single HRU run

If you get this far then SUMMA is installed correctly and functional.

Continue reading SUMMA configuration to learn more about how to configure SUMMA for your application. We strongly recommend that you get the test applications to help you get started.


SUMMA is distributed under the GNU Public License Version 3. For details see the file COPYING in the SUMMA root directory or visit the online version.