Continuous simulations of urban stormwater runoff and total suspended solids loads: influence of varying climatic inputs and catchment imperviousness

Potential implications of climate change for future stormwater management were addressed by undertaking continuous simulations of runoff and total suspended solids (TSS) loads for three urban catchments, with imperviousness varying from 23 to 63%, which were exposed to five rainfall regimes during the snow-free part of the year: the current climate and four climate change scenarios projecting higher rainfalls. Simulated runoff volumes increased in all the future scenarios, particularly in the sub-arctic climate and the fixed uplift scenario (plus20) indicating appreciable rainfall increases. Simulated runoff volumes increased depending on the projected increases in rainfall and increasing runoff contributions from pervious areas when more intense future rainfalls exceeded hydrologic abstractions. The increased runoff volumes then contributed higher TSS loads, which were highly variable for the rainfall regimes tested. In cold climate regions, residues of solids from winter road maintenance may contribute to high initial accumulations of TSS on the catchment surface and high washed off loads. In general, the study suggests that intermediate design-life stormwater management facilities require flexible design allowing for future step-wise adaptation by gradually increasing design capacities and modifying treatment trains.