HYDROLOGICAL PROCESSES Hydrol. Process. 24, 775–788 (2010) Published online 26 January 2010 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/hyp.7531 The inﬂuence of DEM resolution on simulated solar radiation-induced glacier melt Chris Hopkinson, 1 * Laura Chasmer, 2 Scott Munro 3 and Michael N. Demuth 4 1 Applied Geomatics Research Group, Centre of Geographic Sciences, 50 Elliot Road, Lawrencetown, Nova Scotia, B0S 1M0, Canada 2 Cold Regions Research Centre, Wilfrid Laurier University, Waterloo, Ontario, Canada 3 Department of Geography, University of Toronto, Mississauga, Ontario, Canada 4 Natural Resources Canada, Geological Survey of Canada, Ottawa, Ontario, Canada Abstract: The inﬂuence of digital elevation model (DEM) resolution to modelled glacier melt during peak melt production was evaluated by performing a clear sky GIS radiation simulation over the Peyto Glacier in the Canadian Rockies. DEMs were generated at eight resolutions ranging from 1 m to 1000 m grid spacing from airborne lidar data. When applied to the planar area (PA) of the terrain, it was found that total melt increased with DEM resolution (r 2 D 0Ð63) by 4% over 3 orders of magnitude. This systematic scaling-effect was mitigated at the basin scale, however, when the DEM slope variant area (SVA) was used to account for the increased divergence from PA as resolution increases. However, even after the inclusion of SVA in glacier surface melt simulations, localized melt variations with scale were still evident in the ablation and accumulation zone observations. In the ablation zone, there was a systematic increase in simulated melt (¾4%) as resolution decreased from 1 m to 1000 m (r 2 D 0Ð89), with the opposite effect in the accumulation zone (r 2 D 0Ð81). DEM resolution also affected the diurnal melt cycle, such that for the entire glacier there was a tendency for a morning over-estimation and afternoon underestimation of melt rate with decreasing resolution. For the accumulation zone, there was an increased melt rate at low resolutions occurring in the afternoon, while in the ablation zone there was a tendency for increasing melt rates with decreasing resolution throughout the day. These localized spatio-temporal variations in simulated melt are largely due to the lowering of ridges and raising of valley ﬂoors that occur as resolution decreases. This scale dependence in the representation of terrain morphology directly controls the pattern and relative proportion of direct beam shadowing over actively melting surfaces and thereby has a systematic inﬂuence on the grid cell-level hydrological balance. It is recommended that GIS-based glacier melt modelling routines take into account the slope area of grid cells, while noting that the choice of DEM scale can have a discernible and systematic inﬂuence on modelled runoff magnitude. It is important to note that while higher grid resolutions mitigate the effect of terrain smoothing on spatio-temporal melt patterns, lower resolutions actually mitigate the systematic error associated with assuming all surface areas are planar. Copyright  2010 John Wiley & Sons, Ltd and Her Majesty the Queen in right of Canada. KEY WORDS DEM resolution; lidar; scaling; radiation balance; glacier melt; GIS Received 14 January 2008; Accepted 12 October 2009 INTRODUCTION In western Canada, glaciers play an important role in augmenting water resources and moderating river ﬂow variations (Young, 1991; Hopkinson and Young, 1998). As glacier areas continue to diminish and stresses on water resources increase, there is great interest in accu- rately predicting future glacial melt. Operational regional scale hydrological models are frequently used to quan- tify the impacts of changing glacier dimensions to river runoff (e.g. Demuth and Pietroniro, 2002; Comeau et al., 2009). However, as landcover and terrain data resolu- tions improve, there is a need to quantify the impacts of the environmental parameter simpliﬁcations inherent within models. Previous research has demonstrated that digital elevation model (DEM) accuracy increases with resolution (Li, 1992) and that derived hydrological model * Correspondence to: Chris Hopkinson, Applied Geomatics Research Group, Centre of Geographic Sciences, 50 Elliot Road, Lawrencetown, Nova Scotia, B0S 1M0, Canada. E-mail: chris.hopkinson@nscc.ca parameters are sensitive to DEM quality (Wise, 2000; Wechsler, 2007). With the growing availability of high-resolution ter- rain and landcover image data layers that provide impor- tant hydrological information about the landscape, GIS modelling approaches are becoming popular for sim- ulation of runoff. As glacial melt process understand- ing and model parameterizations become more sophis- ticated (e.g. Arnold et al., 1996; Munro, 2004; Hock, 2005), and computing capability more powerful, there follows an increased need to utilize the most spatially explicit data products available; e.g. airborne lidar (light detection and ranging) DEM datasets. In alpine envi- ronments, for example, it has been shown that while accurate watershed area, hypsometry and stream topol- ogy can be derived from high-resolution lidar DEMs, signiﬁcant errors can result when the same attributes are derived from publicly available 20 m contour data sources (Hopkinson et al., 2009). It is generally accepted that the magnitude of derived watershed attribute errors becomes more signiﬁcant as resolution decreases, as the Copyright  2010 John Wiley & Sons, Ltd and Her Majesty the Queen in right of Canada.