Estimation and Evaluation
of Spatially Distributed Snowmelt Model Parameters
Using the Modular Modeling System (MMS)
George H. Leavesley1, Roland J. Viger1, Lauren E. Hay1,
and Steven L. Markstrom1
The U.S. Geological Survey (USGS) Modular Modeling System (MMS) is an integrated system of
computer software developed to provide a framework for the development, integration, application,
and analysis of hydrologic and ecosystem models. MMS uses a library of compatible modules and
models for simulating a variety of hydrologic and ecosystem processes. A geographic information
system (GIS) interface, the GIS Weasel, has been developed to support MMS in model development,
application, and analysis. The GIS Weasel permits application of a variety of GIS tools to delineate,
characterize, and parameterize the topographic, hydrologic, and biologic features of a physical sys-
tem for use in a variety of lumped- and distributed-parameter modeling approaches.
A major difficulty in the application of distributed-parameter models has been the general lack of
objective methods for parameter estimation. To address this problem, a number of parameter-
estimation methods are being developed and evaluated using available digital databases, MMS, and
the GIS Weasel. Databases used in this study were USGS 3-arc second digital elevation models,
State Soils Geographic (STATSGO) 1-km gridded soils data, and Forest Service 1-km gridded vege-
tation type and density data.
Initial research is being conducted using the distributed snowmelt-model component of the USGS
Precipitation-Runoff Modeling System (PRMS). PRMS uses an energy-balance approach to simu-
late the initiation, accumulation, and melt processes of a snowpack. Distributed PRMS parameters
estimated using the digital databases include slope, aspect, elevation, soil type, available water-
holding capacity of the soil, vegetation type, vegetation cover density, solar radiation transmission
coefficient, and interception-storage capacity for each hydrologic response unit (HRU) delineated.
Precipitation distribution was computed using selected precipitation-elevation distribution method-
ologies coupled with MMS.
Evaluation of estimated parameters on four basins in the Rocky, Sierra-Nevada, and Cascade moun-
tain ranges showed reasonable simulations of snow accumulation and melt, and of streamflow tim-
ing and volume. Robustness of parameter estimates and the accuracy of simulation results were a
function of database accuracy, resolution, and scale, as well as the uncertainties associated with
precipitation distribution and basic model conceptualization. While initial evaluation efforts are
being focused on PRMS applications in the United States, the tools provided by MMS and the GIS
Weasel are generic and are applicable to a wide variety of distributed-parameter snowmelt models
and geographic regions. Additional models and regional data sets will be added to the analysis in the
next phase of this investigation.
1 U.S. Geological Survey, WRD, Box 25046, MS 412, Denver Federal Center, Denver, Colorado 80225, USA