In our 2010 paper on TopoToolbox published in Environmental Modelling and Software, we have introduced a matrix algebraic approach to calculate flow accumulation. In a recent paper in Water Resources Research, Alan Richardson and colleagues take this approach a step further by presenting a method that enables implicit, parallizable solving of the flow accumulation equation by a preconditioned iterative solver. Their approach leads to significant speed-ups particularly for processing large datasets on many-core computational systems such as large GPU clusters. In addition, this method is particularly suited in situations when drainage areas need to be calculated very frequently such as in landscape evolution models (LEMs) since upslope areas calculated in a previous time step can be used as initial guess for the next iteration. When drainage patterns stabilize during a simulation, this may speed up such calculations tremendously.