Simulation of runoff from the Navarro watershed in Costa Pica was undertake
n using the U.S. Geological Survey's Precipitation Runoff Modeling System,
developed and operated within the Modular Modeling System. A geographic inf
ormation system (GIS) database of watershed characteristics, and GIS-based
methodology for delineating modeling response units (MRU) were utilized to
enhance the spatial representation of watershed features and physical proce
sses. Simulations were carried out using a series of MRU resolutions (from
90 m(2) to 1,260 m(2)) in order to determine the range through which the hy
drologic response could be accurately modeled. Fractal characterization pro
vided a method to measure the relationship of the MRU patterns (based prima
rily on land cover) at the different resolutions. The range of self-similar
ity of the MRU patterns, as determined by fractal characterization, was com
pared to the range of resolutions through which accurate hydrologic simulat
ions were achieved. The results from this research revealed a strong corres
pondence between the two ranges, and indicate that a range of data resoluti
ons may be useful in representing tropical watershed characteristics for hy
drologic modeling and watershed management.