Yuri Kim
GEOG711
Term project proposal first draft
Nov. 6, 2007
A comparison of RHESSys and SWAT for modeling of water and nitrogen yield
1. Introduction
There are different process based modeling approaches to understand and simulate
hydrologic and nutrient process. It can range from empirical to physically based models
and from lumped to fully distributed models. In this context, Regional Hydro-Ecologic
Simulation System (RHESSys) and Soil and Water Assessment Tool (SWAT) represent
different modeling approaches. The most prominent difference between RHESSys and
SWAT is spatial representation; RHESSys is based on hierarchical and distributed
elements with spatial relation, whereas SWAT is composed of hydrologic response units
(HRU) without spatial position within a watershed. Also the methods that explain
hydrologic and nutrient processes are different in RHESSys and SWAT. Therefore,
comparing RHESSys and SWAT will show how these two models are differently applied
and how the simulation results differently or identically explain water and nutrient
process.
2. Objective
The main purpose of this study is comparing framework, algorithms, parameter values
and output results of these two models. Also it would be interesting to see how well these
two modeling work can simulate water yield changing pattern in response of land use
change during long term simulation.
3. Method
The simulation targets of RHESSys and SWAT are not identical; RHESSys is for water,
carbon and nitrogen, and SWAT is for water, sediment, nitrogen, phosphorous and
pesticide. Thus, water and nitrogen, the common features of two models, are appropriate
for the output comparison with daily, monthly, and annual temporal scales.
4. Study sites
The Flat river watershed mostly located in the Person County of North Carolina is one of
the head water areas of Falls Lake, the water source of the Raleigh area. The land use
history of Flat river watershed demonstrates that considerable portion of this area was
actively used for agricultural activity at least by late 1930’s, but now it has been naturally
changed to forest area. For a control watershed, the Linville river watershed is selected as
a long term forested area.
5. Expected results
The hydrologic simulation will produce water distribution in each hydrologic component:
soil water, total stream flow composition, evapotranspiration, etc. The nitrogen modeling
will also indicate nitrogen process and yield soil and water (kg N/ha with timescale).