PRMS: Precipitation-Runoff Modeling System
VERSION/DATE: Version 2.1 1/17/96
OPERATING SYSTEM: DOS
PRMS - Precipitation-Runoff Modeling System By G. H. Leavesley, R. W. Lichty, B. M. Troutman, and L. G. Saindon DATE: 1983
For installation of PRMS 1 megabyte of free disk space is needed.
To run PRMS, the following are necessary: - 386 or greater processor - math coprocessor - 2 megabytes of combined free extended memory and free disk space on installation drive (the greater proportion available as memory, the better performance will be)
The concepts, structure, theoretical development, and data requirements of the precipitation-runoff modeling system (PRMS) are described. The precipitation-runoff modeling system is a modular-design, deterministic, distributed-parameter modeling system developed to evaluate the impacts of various combinations of precipitation, climate, and land use on streamflow, sediment yields, and general basin hydrology. Basin response to normal and extreme rainfall and snowmelt can be simulated to evaluate changes in waterbalance relationships, flow regimes, flood peaks and volumes, soil- water relationships, sediment yields, and ground-water recharge. Parameter-optimization and sensitivity analysis capabilities are provided to fit selected model parameters and evaluate their individual and joint effects on model output. The modular design provides a flexible framework for continued model-system enhancement and hydrologic-modeling research and development.
The precipitation-runoff modeling system (PRMS) is a modular-design modeling system that has been developed to evaluate the impacts of various combinations of precipitation, climate, and land use on surface-water runoff, sediment yields, and general basin hydrology. Basin response to normal and extreme rainfall and snowmelt can be simulated on various combinations of land use to evaluate changes in water-balance relationships, flow regimes, flood peaks and volumes, soil-water relationships, sediment yields, and ground-water recharge. PRMS is a deterministic physical-process modeling system. To reproduce the physical reality of the hydrologic system as closely as possible, each component of the hydrologic cycle is expressed in the form of known physical laws or empirical relationships that have some physical interpretation based on measurable watershed characteristics.
The modular design of PRMS provides a flexible modeling capability. Each component of the hydrologic system is defined by one or more subroutines that are maintained in a computer-system library. All subroutines are compatible for linkage to each other. Given a specific hydrologic problem and its associated data constraints, the user can select an established model from the library or can design his own model using selected library and user-supplied subroutines. The library also contains subroutines for parameter optimization, sensitivity analysis, and model output handling and analysis. The initial system subroutines were obtained by modularizing an event-type distributed routing rainfall-runoff model (Dawdy and others, 1978) and a daily flow rainfall- and snowmelt-runoff model (Leavesley and Striffler, 1978), and by writing new algorithms for processes and procedures not available in these models. Additional subroutines will be added and existing subroutines will be modified and improved as experience is gained from model applications in various climatic and physiographic regions.
PRMS is designed to function either as a lumped- or distributed- parameter type model and will simulate both mean daily flows and stormflow hydrographs. PRMS components are designed around the concept of partitioning a watershed into units on the basis of characteristics such as slope, aspect, vegetation type, soil type, and precipitation distribution. Each unit is considered homogeneous with respect to its hydrologic response and 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 HRU'S, weighted on a unit-area-basis, produces the daily system response and streamflow from the watershed. Partitioning provides the ability to impose land-use or climate chances on parts or all of a watershed, and to evaluate resulting hydrologic impacts on each HRU and on the total watershed.
Input variables include descriptive data on the physiography, vegetation, soils, and hydrologic characteristics of each HRU, and on the variation of climate over the watershed. The minimum driving variables required to run in the daily-flow mode are (1) daily precipitation, and (2) maximum and minimum daily air temperatures. Daily pan-evaporation data can be substituted for air temperature for situations where snowmelt simulation is not required; daily solar radiation data are recommended when snowmelt will be simulated. To simulate stormflow hydrographs, rainfall depths for time intervals of 60 minutes or less are required. PRMS is designed to run with data retrieved directly from the U.S. Geological Survey's National Water Data Storage and Retrieval (WATSTORE) system (Hutchinson, 1975). However, PRMS also can use data not stored on the WATSTORE system. Programs are available to read and reformat these data to make them model- compatible.
The modular system approach provides an adaptable modeling system for both management and research applications. For management problems, a model can be tailored to geographic region, data, and problem characteristics. Research applications include development of new model components and the testing and comparison of various approaches to modeling selected components of the hydrologic cycle. New model components proposed as future additions to PRMS include water-quality components and expanded saturated-unsaturated flow and ground-water flow components.
This documentation is designed to provide the user with the basic philosophy and structure of PRMS, instructions for application of established models designed as cataloged procedures, and instructions for interaction with the PRMS library to permit user additions or modifications of model components. The components and subroutines described in this document are those available at the time of publication. However, the library is dynamic and will be enhanced and updated through time. This manual will be updated to reflect major additions and changes through manual inserts or republications.
All components of PRMS except the hydrologic and meteorologic data retrieval subroutines (DVRETR and UVRET) are written in FORTRAN. PRMS data sets are handled using an indexed sequential (ISAM) file structure. Because PRMS has been developed on an AMDAHL computer system, DVRETR and UVRET are written in PL/I programming language. To run PRMS on computer systems that don't have ISAM file or PL/I-FORTRAN interface capabilities will require modifications to DVRETR and UVRET. Descriptions of DVRETR and UVRET are given in attachment VII to facilitate user modifications. Future enhancement of the data management components includes the development of a FORTRAN-based data-management system. This system will permit creation, editing, and limited analysis of a PRMS data set.
The PRMS structure has three major components. The first is the data- management component. It handles the manipulation and storage of hydrologic and meteorologic data into a model-compatible direct access file. The second is the PRMS library component. This component consists of both a source-module library and a load-module library for the storage of the compatible subroutines used to define and simulate the physical processes of the hydrologic cycle. In addition, it contains the parameter- optimization and sensitivity-analysis subroutines for model fitting and analysis. The third component is the output component that provides the model output handling and analysis capabilities.
The three PRMS components are shown schematically in figure 1. Hydrologic and meteorologic field data are collected and stored in either user data files or the U.S. Geological Survey's WATSTORE system. Data interface programs accept data from these two sources and convert and store the data in an index-sequential (ISAM) file, which is fully model- compatible. The precipitation-runoff model either is selected as a cataloged procedure from the PRMS library or is created from PRMS library- and user-supplied subroutines. The model reads initialization and basin characteristics information from card-deck input and accesses the ISAM data file for hydrologic and meteorologic data required for model operation. Model outputs can be printed and stored for further analysis.