Landscape controls on long-term runoff in sub-humid heterogeneous Boreal Plains catchments

We compared median runoff (R) and precipitation (P) relationships over 25 years from 20 meso-scale (50 to 5,000 km2) catchments on the Boreal Plains (BP), Alberta, Canada, to understand controls on water sink and source dynamics in water-limited, low-relief northern environments. Long-term catchment R and runoff efficiency (RP-1) were low and varied spatially by over an order of magnitude (3 to 119 mmyr-1, 1 to 27%). Inter-catchment differences were not associated with small variations in climate. The partitioning of P into evapotranspiration (ET) and R instead reflected the interplay between underlying glacial deposit texture, overlying soil-vegetation land cover, and regional slope. Correlation and PCA results show that peatland-swamp wetlands were the major source areas of water. The lowest estimates of median annual catchment ET (321 to 395 mm) and greatest R (60 to 119 mm, 13 to 27% of P) were observed in low-relief, peatland-swamp dominated catchments, within both fine-textured clay-plain and coarse-textured glacial deposits. In contrast, open-water wetlands and deciduous-mixedwood forest land covers acted as water sinks, and less catchment R was observed with increases in proportional coverage of these land-covers. In catchments dominated by hummocky moraines, long-term runoff was restricted to 10 mmyr-1, or 2% of P. This reflects the poor surface-drainage networks and slightly greater regional slope of the fine-textured glacial deposit, coupled with the large soil-water and depression storage and higher AET of associated shallow open-water marsh wetland and deciduous-forest land covers. This inter-catchment study enhances current conceptual frameworks for predicting water yield in the BP based on the sink and source functions of glacial landforms and soil-vegetation land covers. It offers the capability within this hydro-geoclimatic region to design reclaimed catchments with desired hydrological functionality and associated tolerances to climate or land-use changes, and inform land management decisions based on effective catchment-scale conceptual understanding.