Precipitation Runoff Modeling System (PRMS/OMS) 
The Precipitation‑Runoff Modeling System (PRMS/OMS) is a modular, distributed‑parameter, physical‑process watershed model that was developed to evaluate the effects of various combinations of precipitation, climate, and land use on watershed response. Response to normal and extreme rainfall and snowmelt can be simulated to evaluate changes in water‑balance relations, flow regimes, flood peaks and volumes, soil‑water relations, and ground‑water recharge.
PRMS was originally developed as a single FORTRAN program composed of subroutines, each representing an individual process in the hydrologic cycle. While reasonable in concept and computationally efficient, experience with adding process components to the original code proved the modular-design and user-modifiable features of that version to be less than adequate. As a result, the architecture and modular structure of PRMS were redesigned. This design formed the basis for the USGS Modular Modeling System (MMS) and enabled the addition of new process algorithms and the enhancement of many of the features and capabilities of PRMS.
PRMS has now been integrated into the Object Modeling System (OMS). The FORTRAN modules have been ported to Java to facilitate their easier integration, scalability, portability and use with other models and model components being integrated into OMS as well. PRMS/OMS is being used within USDA for water supply forecasting at the NRCS National Water and Climate Center.
Distributed‑parameter capabilities are provided by partitioning a watershed into units, using characteristics such as slope, aspect, elevation, vegetation type, soil type, and precipitation distribution. Each unit is assumed to be homogeneous with respect to its hydrologic response and to the characteristics listed above; each unit is called a hydrologic response unit (HRU). A water balance and an energy balance are computed daily for each HRU. The sum of the responses of all HRUs, weighted on a unit‑area basis, produces the daily watershed response.
Watershed response can be simulated at both a daily and a storm time scale. In the daily mode, hydrologic components are simulated as daily average or total values. Streamflow is computed as a mean daily flow. In the storm mode, selected hydrologic components are simulated at time intervals that can range from less than one to 60 minutes. The time step must be constant within a storm but could be different for each storm. Continuity of mass is maintained as the model moves from daily mode to storm mode and back to daily mode. Storm hydrographs for selected rainstorms can be simulated in storm mode.
For storm-mode computations, a watershed is conceptualized as a series of interconnected flow‑plane and channel segments. An HRU is considered the equivalent of a single flow plane. The shape of the flow plane is assumed to be rectangular, with the length of one side of rectangle equal to the length of the channel segment that receives runoff from the flow plane. The flow-plane width is computed by dividing the HRU area by the channel segment length. All flow planes are assumed to connect to a channel segment. Cascading flow planes are not currently supported, but a module to support this capability is being developed.
Figure 1: PRMS Process Components
The process components simulated in PRMS are shown schematically in Figure 1. The processes shown are generic in name. Thus Figure 1 is a template for model design and not a flow chart describing a unique set of process algorithms. In the OMS design, process selection is part of the model building process. Each alternative computational method for a given process is a component that can be combined with other process and accounting components to build a unique model for a specific application.
A detailed description of the computational methods and equations used in PRMS was provided in Leavesley et al. (1983) and Leavesley and Stannard (1995). This material has been rewritten and is included in detailed documentation for each PRMS module. This documentation link is provided above. Component documentation includes the listing and definition of all parameters and variables used in the component, the equations used in the computational algorithms, and a text description of the component process and function.
Install PRMS Modeling Project
The basic OMS project structure is composed of a master directory, here PrmsOmsWork and four subdirectories.
Unzip the PRMS-prj.zip file and extract the contents to C:\ to be consistent with the paths used in the PRMS tutorials. However, it is not mandatory that the PrmsOmsWork directory be located at C:\ and it can be placed anywhere in the users directory structure.
The PRMS project contains data and simulation related files for the East Fork Carson River in California.
Execution of the models and tools provided in the jar file is supported by the use of an OMS3 Console.
The purpose of this example application is to provide a simple demonstration of how to execute a model in the OMS3 Console and to insure that the downloaded materials are installed correctly. In this example the PRMS model configuration named PrmsDdJh is being used. More detailed information on all PRMS model configurations, and the associated data and parameter files required for each, are provided in the Detailed Description and Execution of PrmsOms Model Configurations section below. PrmsDdJh will be run on the East Fort Carson River basin in California.
Model execution information is provide by a .sim file. A .sim file is a script that identifies the specific model to be executed, the data and parameter file locations, user selected output variables, selected statistical measures of model performance to be computed, selected output analyses to be displayed graphically.
To execute efc.sim, click on the Run icon in the efc.sim tab toolbar or type Ctrl+r. Notification of errors, selected model output, and model completion information will be written in the lower window field of the Console.
To view the plots specified in the analysis section of the .sim, click on the Analysis icon in the efc.sim tab toolbar.
This will open the Simulation Output graphical analysis window. Each of the timeseries plots specified in the Analysis section of the .sim will appear as a tab in the analysis window. Click on an individual tab to view the output.
Detailed Description and Execution of PrmsOms Model Configurations
Leavesley, G.H., Lichty, R.W., Troutman, B.M., and Saindon, L.G., 1983, Precipitation-runoff modeling system--User's manual, U.S. Geological Survey Water Resources Investigation Report 83-4238, 207 p.
Leavesley, G.H., and Stannard, L.G., 1995, The precipitation-runoff modeling system PRMS, in Singh, V.P., ed., Computer Models of Watershed Hydrology: Highlands Ranch, CO, Water Resources Publications, p. 281-310.
Leavesley, G.H., Markstrom, S.L., and Viger, R.J., 2006, USGS Modular Modeling System (MMS) – Precipitation-Runoff Modeling System (PRMS), in Singh, V.P. and Frevert, D.K., (Eds.), Watershed Models, CRC Press, p. 159-177.
Markstrom, S.L., Niswonger, R.G., Regan, R.S., Prudic, D.E., and Barlow, P.M., 2008, GSFLOW—Coupled ground-water and surface-water flow model based on the integration of the Precipitation-Runoff Modeling System (PRMS) and the Modular Ground-Water Flow Model (MODFLOW-2005): U.S. Geological Survey Techniques and Methods 6-D1, 240 p.
[#1]To distinguish the OMS version of PRMS from the USGS MMS version, the OMS version is termed PRMS/OMS. While there is agreement in the algorithm composition of most of the comparable MMS and OMS modules at this time, there is no guarantee that future PRMS/OMS components will replicate all future PRMS/MMS modules. The USGS provides collaborative support for the conversion of MMS PRMS components to PRMS/OMS components. However, USGS is not responsible for the development, validation, distribution, or support of PRMS/OMS.