Hydrologic Model Parameter Estimation in Ungauged Basins using Simulated
SWOT Discharge Observations
Abstract
In situ gauge networks are often used in hydrologic model calibration,
but these networks are limited or nonexistent in many regions. The
upcoming Surface Water Ocean Topography (SWOT) mission promises to fill
this observation gap by providing discharge estimates for rivers wider
than 100 meters. SWOT observation utility for model parameter selection
in regions devoid of in situ gauges is assessed using proxy SWOT
discharge estimates derived from an observing system simulation
experiment and Monte Carlo methods. The sensitivity of the parameter
selection to measurement error and observation frequency is also
evaluated. Single- and multi-point parameter selection are performed for
ten sub-basins within the Susitna and upper Tanana river basins in
Alaska. SWOT is expected to observe Alaskan river points 4-7 times per
21-day repeat cycle with 120-km swath coverage. For an expected SWOT
measurement error of 35%, parameter estimation is successful for 50%
(90%) of sub-basins using single- (multi-) point parameter selection.
Decreasing observation frequency to simulate lower latitudes resulted in
success for only 10% of midlatitude and tropical sub-basins for
single-point selection, whereas multi-point selection was successful in
80% (60%) of midlatitude (tropical) sub-basins. Single-point parameter
selection is more sensitive to measurement error than multi-point
parameter selection. The results strongly support the use of multi-point
over single-point parameter selection, yielding robust results nearly
independent of observation frequency. Most importantly, this study
suggests SWOT can be used to successfully select hydrologic model
parameters in basins without an in situ gauge network.