How might Canadian Shield surface water drainage pattern change in a wetter climate?

The Canadian Shield (CS), a vast deglaciated Precambrian crystalline bedrock region of northern North America, is poorly drained and contains more lakes than anywhere else on Earth. Despite observations and climate model projections of increasing precipitation over the region, the effects of a wetter Arctic climate on CS drainage patterns are unknown, and made even more uncertain by the region's deranged, poorly mapped surface drainage pattern. Using the 90 m Merit Digital Elevation Model (MERIT DEM), we examine current and plausible future CS drainage patterns based on topographic inundation modeling. CS surface runoff is characterized by 'fill-and-spill' hydrology, in which topographic depressions fill with water when upstream depressions fill and overtop their storage capacities and flow downstream. In addition to typical DEM artifacts, numerous CS physical depressions create abundant depression storage and fill-and-spill junctures. To simulate different water balance scenarios, we model changing depression storage and hydrologic connectivity across the CS landscape assuming different uniformly applied inundation depths (0.05 - 2.0 m) as a proxy for increasing water balance scenarios. Due to CS crystalline bedrock substrate and permafrost, we assume negligible subsurface infiltration and storage. Our results show that just a ~1 m increase in regional water balance would cause a ~200% increase in the number of CS topographic depressions experiencing fill-and-spill hydrology, and increase the number of interconnected lakes from approximately 1.3M to 3.8M. Many new streams would also form. While the overall drainage pattern remains stable even up to a +2 m increase in inundation, we conclude that CS surface water depression storage and hydrological connectivity is highly sensitive to future changes in regional water balance. Future work will examine the sensitivity of CS depression storage, hydrological connectivity, and drainage pattern to changing future water balance as projected by regional climate models.