SUMMA or the Structure for Unifying Multiple Modeling Alternatives is a hydrologic modeling approach 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:
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.
SUMMA is an open-source project, with code made available under version 3 of the GNU General Public License (GPLv3). Among other things this means that we require that if you make changes to SUMMA (which we strongly encourage) and you want to distribute those changes, then all released improved versions must also be free software.
The SUMMA source code is maintained and distributed through the SUMMA page on github. This site also maintains information on model installation. Most of the active development on SUMMA is managed and discussed on this page as well.
This tar archive contains a series of test cases for SUMMA:
There are two classes of test cases:
The motivation for SUMMA's development and some initial examples are described in a two-part paper in Water Resources Research. If you use SUMMA, please credit these two publications:
Clark, M. P., B. Nijssen, J. Lundquist, D. Kavetski, D. Rupp, R. Woods, E. Gutmann, A. Wood, L. Brekke, J. Arnold, D. Gochis, and R. Rasmussen, 2015a: A unified approach to process-based hydrologic modeling. Part 1: Modeling concept. Water Resources Research, 51, doi: 10.1002/2015WR017198.
Clark, M. P., B. Nijssen, J. Lundquist, D. Kavetski, D. Rupp, R. Woods, E. Gutmann, A. Wood, D. Gochis, R. Rasmussen, D. Tarboton, V. Mahat, G. Flerchinger, and D. Marks, 2015b: A unified approach for process-based hydrologic modeling: Part 2. Model implementation and example applications. Water Resources Research, 51, doi: 10.1002/2015WR017200
SUMMA's implementation is described in detail in an NCAR Technical Note:
Clark, M. P., B. Nijssen, J. Lundquist, D. Kavetski, D. Rupp, R. Woods, E. Gutmann, A. Wood, L. Brekke, J. Arnold, D. Gochis, R. Rasmussen, D. Tarboton, V. Mahat, G. Flerchinger, and D. Marks (2015a), The Structure for Unifying Multiple Modeling Alternatives (SUMMA), version 1: Technical description, NCAR Technical Note NCAR/TN-514+STR, 54 pp., National Center for Atmospheric Research, Boulder, Colo., doi:10.5065/D6WQ01TD.
Martyn Clark, RAL Hydrometeorology Applications Program
Bart Nijssen, UW Hydro | Computational Hydrology
Jessica Lundquist, Mountain Hydrology Research, University of Washington
Dmitri Kavetski, School of Civil, Environmental and Mining Engineering