Baseflow is an important component in hydrological modeling. The complexstreamflow recession process complicates the baseflow simulation. In order tosimulate the snow and/or glacier melt dominated streamflow receding quicklyduring the high-flow period but very slowly during the low-flow period in riversin arid and cold northwest China, the current one-reservoir baseflow approachin SWAT (Soil Water Assessment Tool) model was extended by adding a slow-reacting reservoir and applying it to the Manas River basin in the TianshanMountains. Meanwhile, a digital filter program was employed to separatebaseflow from streamflow records for comparisons. Results indicated that thetwo-reservoir method yielded much better results than the one-reservoir onein reproducing streamflow processes, and the low-flow estimation was improvedmarkedly. Nash-Sutcliff efficiency values at the calibration and validationstages are 0.68 and 0.62 for the one-reservoir case, and 0.76 and 0.69 forthe two-reservoir case. The filter-based method estimated thebaseflow index as 0.60, while the model-based as 0.45. The filter-basedbaseflow responded almost immediately to surface runoff occurrence at onset ofrising limb, while the model-based responded with a delay. In consideration ofwatershed surface storage retention and soil freezing/thawing effects oninfiltration and recharge during initial snowmelt season, a delay response isconsidered to be more reasonable. However, a more detailed description offreezing/thawing processes should be included in soil modules so as todetermine recharge to aquifer during these processes, and thus an accurateonset point of rising limb of the simulated baseflow.
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