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Introduction

Goal

The aim of this article is to provide an assessment of the performance of spwb_land() for the prediction of watershed outflow. To this aim, we simulate hydrological processes in a set of benchmark watersheds and compare the model predictions of watershed outflow against measurements obtained using river gauges at watershed outlets.

Simulation procedure

For each watershed, the following procedure has been conducted:

  1. Initial warm-up simulation for a specified number of years
  2. Simulation for the period with observed data before calibrating watershed parameters
  3. Manual calibration of watershed parameters (to be replaced with automatized calibration)
  4. Final simulation for the period with observed data after calibrating watershed parameters.

Goodness-of-fit statistics

The following goodness of fit statistics are calculated using package hydroGOF:

  • Nash-Sutcliffe Efficiency (NSE): This coefficient is sensitive to extreme values and might yield sub-optimal results when the dataset contains large outliers.
  • Kling–Gupta efficiency (KGE): Provides a decomposition of the Nash-Sutcliffe efficiency, which facilitates the analysis of the importance of different components (bias, correlation and variability).
  • Index of agreement (d): Initially proposed by Willmott (1981) to overcome the drawbacks of the R2, such as the differences in observed and predicted means and variances (Legates and McCabe, 1999). d is also dimensionless and bounded between 0 and 1 and can be interpreted similarly to R2.
  • Volumetric efficiency index (VE): Originally proposed by Criss and Winston (2008) to circumvent some of the NSE flaws. VE values are also bounded [0, 1] and represent the fraction of water delivered at the proper time.
  • Root mean squared error (RMSE): The usual estimation of average model error (i.e. the square root of mean squared errors).

Hydrological analysis

Watershed (TETIS) parameters

The following table contains the set of TETIS parameters employed in spwb_land() simulations on all watersheds, before and after calibration:

medfateland medfate model watershed Calibration R_localflow R_interflow R_baseflow n_interflow n_baseflow num_daily_substeps rock_max_infiltration deep_aquifer_loss
2.5.1 4.8.0 tetis aiguadora before 1 50 5 1.0 1.0 4 10 0
2.5.1 4.8.0 tetis aiguadora after 1 8 1 0.5 0.7 4 10 5
2.5.1 4.8.0 tetis aiguadora before 1 50 5 1.0 1.0 4 10 0
2.5.1 4.8.0 tetis aiguadora after 1 8 1 0.5 0.7 4 10 5
2.5.2 4.8.0 tetis aiguadora before 1 50 5 1.0 1.0 4 10 0
2.5.2 4.8.0 tetis aiguadora after 1 8 1 0.5 0.7 4 10 5

Evaluation results

AIGUADORA watershed with TETIS and version 2.4.6

Graphical evaluation

Daily

Monthly

Goodness-of-fit

Scale Calibration NSE KGE d VE RMSE
Daily Before -10.432 -2.136 0.614 -3.571 2.487
Daily After -0.748 0.132 0.306 -0.224 0.973
Monthly Before -21.961 -3.604 0.652 -3.483 2.352
Monthly After -1.519 -0.209 0.325 -0.054 0.779

Hydrological analysis

Density distribution

Percentiles

Observed Uncalibrated Calibrated
1% 0.040 0.980 0.051
5% 0.060 1.129 0.095
10% 0.070 1.254 0.134
15% 0.080 1.377 0.169
25% 0.110 1.580 0.250
50% 0.250 2.201 0.590
75% 0.520 3.088 1.279
85% 0.820 3.749 1.765
90% 1.150 4.262 2.126
95% 1.724 5.175 2.719
99% 3.370 7.220 4.049

AIGUADORA watershed with TETIS and version 2.5.1

Graphical evaluation

Daily

Monthly

Goodness-of-fit

Scale Calibration NSE KGE d VE RMSE
Daily Before -7.688 -1.721 0.543 -2.851 2.257
Daily After -0.388 0.306 0.466 0.061 0.902
Monthly Before -16.128 -3.002 0.592 -2.804 2.096
Monthly After -0.396 0.139 0.515 0.246 0.598

Hydrological analysis

Density distribution

Percentiles

Observed Uncalibrated Calibrated
1% 0.04 0.861 0.021
5% 0.06 0.995 0.057
10% 0.07 1.111 0.089
15% 0.08 1.227 0.116
25% 0.12 1.404 0.178
50% 0.26 2.006 0.474
75% 0.56 2.910 1.146
85% 0.89 3.576 1.618
90% 1.22 4.132 2.018
95% 1.82 5.035 2.582
99% 3.53 7.443 4.298

AIGUADORA watershed with TETIS and version 2.5.2

Graphical evaluation

Daily

Monthly

Goodness-of-fit

Scale Calibration NSE KGE d VE RMSE
Daily Before -7.688 -1.721 0.543 -2.851 2.257
Daily After -0.388 0.306 0.466 0.061 0.902
Monthly Before -16.128 -3.002 0.592 -2.804 2.096
Monthly After -0.396 0.139 0.515 0.246 0.598

Hydrological analysis

Density distribution

Percentiles

Observed Uncalibrated Calibrated
1% 0.04 0.861 0.021
5% 0.06 0.995 0.057
10% 0.07 1.111 0.089
15% 0.08 1.227 0.116
25% 0.12 1.404 0.178
50% 0.26 2.006 0.474
75% 0.56 2.910 1.146
85% 0.89 3.576 1.618
90% 1.22 4.132 2.018
95% 1.82 5.035 2.582
99% 3.53 7.443 4.298