|Separating wet and dry years to improve calibration of SWAT in Barrett Watershed, southern California
|Gao, X., X. Chen, T.W. Biggs and H. Yao
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|337 km^2 Cottonwood River, a tributary of the Tijuana River that drains to the Barrett Reservoir in far south west California, U.S.
|Hydrological models often perform poorly in simulating dry years in regions with large
inter-annual variability in rainfall. We calibrated the Soil and Water Assessment Tool (SWAT) model
to dry and wet years separately, using the semi-arid Barrett watershed on the west coast of USA as
an example. We used hydrological and meteorological data from 1980–2010 to calibrate the SWAT
model parameters, compared the monthly runoff results simulated by SWAT using a traditional
calibration for the entire runoff series with results using a calibration with the wet and dry year
series, and analyzed differences in the most sensitive parameters between the wet and dry year series.
The results showed that (1) the SWAT model calibrated to the entire runoff series produced significant
differences in simulation efficiency between the wet years and dry years, with lower efficiency during
the dry years; (2) the calibration with separate wet and dry years greatly enhanced the SWAT model’s
simulation efficiency for both wet and dry years; (3) differences in hydrological conditions between
wet and dry years were represented by changes in the values of the six most sensitive parameters,
including baseflow recession rates, channel infiltration rates, Soil Conservation Service (SCS) curve
number, soil evaporation, shallow aquifer flow, and soil water holding capacity. Future work can
attempt to determine the physical processes that underlie these parameter changes and their impact
on the hydrological response of the semi-arid watersheds.
|runoff; dry year; parameter; calibration; SWAT; Barrett watershed