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Milzow C.,Technical University of Denmark | Milzow C.,Institute for Environmental Engineering | Kinzelbach W.,Institute for Environmental Engineering
Water Resources Research | Year: 2010

To be computationally viable, grid-based spatially distributed hydrological models of large wetlands or floodplains must be set up using relatively large cells (order of hundreds of meters to kilometers). Computational costs are especially high when considering the numerous model runs or model time steps necessary in calibration and long-term simulation. To parameterize such models, upscaling procedures are required in furnishing equivalent hydrological model parameters on the grid scale. Here we investigate the effect of a new upscaling technique for hydrological flow parameters dependent upon the small-scale terrain elevation distribution, namely, resistance to flow, infiltration, and depression storage volume. In the new procedure, these hydrological model parameters on the grid scale become functions of the water table elevation. These functions are established by preparatory, nonrecurring, simulations using the highest available topographic data as input. In this way, the variability and spatial correlation of elevation data on the subscale is preserved on the model scale, at least to some extent. The MODFLOW-based hydrological model of the Okavango Wetlands is used as a study case. The effectiveness of the new upscaling technique is judged on the basis of comparison of computed flooding patterns with and without implementation of the new technique. It is shown that model results are considerably influenced by this new more flexible parameterization. The partitioning of flows toward the different distributary systems of the Okavango Wetlands is improved by the new technique. © 2010 by the American Geophysical Union.


Miles E.S.,University of Cambridge | Pellicciotti F.,Institute for Environmental Engineering | Pellicciotti F.,Northumbria University | Willis I.C.,University of Cambridge | And 3 more authors.
Annals of Glaciology | Year: 2016

Supraglacial ponds on debris-covered glaciers present a mechanism of atmosphere/glacier energy transfer that is poorly studied, and only conceptually included in mass-balance studies of debriscovered glaciers. This research advances previous efforts to develop a model of mass and energy balance for supraglacial ponds by applying a free-convection approach to account for energy exchanges at the subaqueous bare-ice surfaces. We develop the model using field data from a pond on Lirung Glacier, Nepal, that was monitored during the 2013 and 2014 monsoon periods. Sensitivity testing is performed for several key parameters, and alternative melt algorithms are compared with the model. The pond acts as a significant recipient of energy for the glacier system, and actively participates in the glacier's hydrologic system during the monsoon. Melt rates are 2-4 cmd-1 (total of 98.5m3 over the study period) for bare ice in contact with the pond, and <1mmd-1 (total of 10.6m3) for the saturated debris zone. The majority of absorbed atmospheric energy leaves the pond system through englacial conduits, delivering sufficient energy to melt 2612m3 additional ice over the study period (38.4m3 d-1). Such melting might be expected to lead to subsidence of the glacier surface. Supraglacial ponds efficiently convey atmospheric energy to the glacier's interior and rapidly promote the downwasting process.

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