Abstract
Abstract The effects of watershed subdivisions on hydrological simulations have not been evaluated in Arctic conditions yet. This study applied the Soil and Water Assessment Tool and the threshold drainage area (TDA) technique to evaluate the impacts of watershed subdivision on hydrological simulations at a 5,913-km2 Arctic watershed, Målselv. The watershed was discretized according to four TDA scheme scales including 200, 2,000, 5,000, and 10,000 ha. The impacts of different TDA schemes on hydrological simulations in water balance components, snowmelt runoff, and streamflow were investigated. The study revealed that the complexity of terrain and topographic attributes altered significantly in the coarse discretizations: (1) total stream length (−47.2 to −74.6%); (2) average stream slope (−68 to −83%); and (3) drainage density (−24.2 to −51.5%). The spatial density of weather grid integration reduced from −5 to −33.33% in the coarse schemes. The annual mean potential evapotranspiration, evapotranspiration, and lateral flow slightly decreased, while areal rainfall, surface runoff, and water yield slightly increased with the increases of TDAs. It was concluded that the fine TDAs produced finer and higher ranges of snowmelt runoff volume across the watershed. All TDAs had similar capacities to replicate the observed tendency of monthly mean streamflow hydrograph, except overestimated/underestimated peak flows. Spatial variation of streamflow was well analyzed in the fine schemes with high density of stream networks, while the coarse schemes simplified this. Watershed subdivisions affected model performances, in the way of decreasing the accuracy of monthly streamflow simulation, at 60% of investigated hydro-gauging stations (3/5 stations) and in the upstream. Furthermore, watershed subdivisions strongly affected the calibration process regarding the changes in sensitivity ranking of 18 calibrated model parameters and time it took to calibrate.
Highlights
The semi-distributed model SWAT (Soil And Water Assessment Tool) (Neitsch et al 2009) was developed to predict the impacts of human activities (Gassman et al 2007) and climate change (Dile et al 2013) on environment and water resources in large complex watersheds
To investigate the effects of watershed subdivisions on the hydrological simulations, the present study focused on the evaluation of the simulation results of water balance components and streamflow
Discrepancies in watershed characteristics and land-use composition resulting from different threshold drainage area (TDA) schemes
Summary
The semi-distributed model SWAT (Soil And Water Assessment Tool) (Neitsch et al 2009) was developed to predict the impacts of human activities (Gassman et al 2007) and climate change (Dile et al 2013) on environment and water resources in large complex watersheds. Lumped models consider the entire watershed/basin as a single system (Devi et al 2015); on the other hand, the semi-distributed models like SWAT divide the whole watershed/basin into smaller sub-watersheds/sub-basins (Daofeng et al 2004; Dwarakish & Ganasri 2015). Choosing the size for the sub-basins influences the. Journal of Water and Climate Change Vol 00 No 0, 2 homogeneous assumption because the larger the sizes of the sub-basins, the higher variable conditions the sub-basins have (Bingner et al 1997). When the sizes of sub-basins are reduced and the number of sub-basins are increased, it significantly influences the amounts of required input data and model parameters, the computational process (Bingner et al 1997), as well as the calibration effort since the large number of sub-basins may require more adjusted model parameters needed to optimize the simulation results and more iterations needed for running the calibration (Rouhani et al 2009)
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