Runoff Threshold Responses in Continental Boreal Catchments: Nexus of Subhumid Climate, Low‐Relief, Surficial Geology, and Land Cover

We examined annual runoff from 20 meso-scale catchments over 25 years, to elucidate how interactions between physiography and long-term weather patterns influence the magnitude of spatial–temporal thresholds in annual runoff responses in water-limited, low-relief, glaciated continental Boreal landscapes. Annual runoff ranged over 2 orders of magnitude (<3 to >300 mm) among catchments receiving similar annual precipitation. Threshold relationships were observed with cumulative regional moisture deficits that reflected spatial–temporal differences in effective storage and antecedent moisture among catchments with differing portions of glacial-deposit and land-cover types. The importance of the glacial-deposit texture and forest-peatland cover on runoff behavior among catchments varied with weather patterns and catchment antecedent moisture states. Dry states yielded low annual runoff that ranged by 2 orders of magnitude (0–80 mm), with higher values in catchments with predominantly coarse-textured deposits. During near normal antecedent moisture, annual runoff remained low (<10 mm) in catchments associated with fine-textured, hummocky landforms and deciduous forests. Annual runoff >10 mm was observed only in catchments with extensive peatlands. Infrequent wet states resulted in increased runoff in all catchments; however, ranges in maximum runoff were associated with heterogeneity in catchment landforms and land covers. Integrating cumulative precipitation with the proportion of glacial-deposit and land-cover types within catchments can (a) represent water cycling and regional sink-source dynamics controlling runoff and (b) provide an effective management framework for predicting climate and land use impacts on regional runoff in water-limited, low-relief, glaciated landscapes such as the Boreal Plain.