3.2.1 Verification against stream gauges
Gauged water heights from five USGS stream gauges within the model domain are retrieved during model simulations at the 15-min interval. Surface water heights from two simulation schemes are extracted at collocated stream gauge locations. It is worth mentioning that the terrain elevation imposes great uncertainties when comparing model simulations to observations, as the sub-grid variation cannot be resolved in the current settings. Despite the resolution mismatch, these gauge readings are still the most widely used source to verify the model performance. Table 4 shows the respective performance for with and without re-infiltration scenarios with respect to observations. The re-infiltration scheme greatly improves the NSE scores (+139.9%) and CC (+7.24%) while reducing RMSE (-18.2%). Especially for the gauge 08075900, there is more than a 400% increase in NSE score, jumping from 0.12 to 0.69. By breaking down the RMSE into systematic error RMSES and random error RMSER, we see the reduced error is largely attributed to minimized systematic error (-31.2%), relative to the random error (-13.1%). The systematic bias is much alleviated by considering the re-infiltration scheme.
The reason for such a leap comes from better characterization of its flow recession limbs, as shown in Figure 6. Both schemes are capable of simulating the peak water height values without delays, but water in the scenario without re-infiltration falls mildly in the recession stage, resulting in much higher water height than the observations. On the other hand, flow for the re-infiltration scenario follows the gauge readings closely, especially after the first peak (from 2017-08-26 to 2017-08-27). Apart from this best-performing gauge, the re-infiltration scheme improves capturing falling water across all the gauge stations, thereby leading to significant performance gains. Consistently, previous studies also highlighted that the re-infiltration markedly reduces recession limbs in the hydrograph (Nahar et al., 2004).
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