Comment on Groundwater Affects the Geomorphic and Hydrologic Properties of Coevolved Landscapes by Litwin et al.

The objective of this comment is to correct two sets of statements in Litwin et al. (2022, https://doi.org/10.1029/2021JF006239), which consider our research work (Bonetti et al., 2018, https://doi. org/10.1098/rspa.2017.0693; Bonetti et al., 2020, https://doi.org/10.1073/pnas.1911817117). We clarify here that (a) the specific contributing area is defined in the limit of an infinitesimal contour length instead of the product of a reference contour width (Bonetti et al., 2018, https://doi.org/10.1098/rspa.2017.0693), and (b) not all solutions obtained from the minimalist landscape evolution model of Bonetti et al. (2020, https://doi. org/10.1073/pnas.1911817117) are rescaled copies of each other. We take this opportunity to demonstrate that the boundary conditions impact the obtained solutions, which has not been considered in the dimensional analysis of Litwin et al. (2022, https://doi.org/10.1029/2021JF006239). We clarify this point by using dimensional analysis and numerical simulations for a square domain, where only one horizontal length scale (the side length l) enters the physical law. Plain Language Summary This comment is focused on rectifying the statements regarding the previous works of Bonetti et al. (2018, https://doi.org/10.1098/rspa.2017.0693) and Bonetti et al. (2020, https://doi.org/10.1073/pnas.1911817117) in Litwin et al. (2022, https://doi.org/10.1029/2021JF006239). We clarify here the definition of the specific contributing area and the role of boundary conditions in the obtained solutions of the landscape evolution model, which has been left unnoticed by Litwin et al. (2022, https://doi. org/10.1029/2021JF006239). Using dimensional analysis and simulations for a square domain, we show that only those solutions remain rescaled copies of each other where the non-dimensional group containing the influence of boundary conditions remains the same. This result was already incorporated in the dimensional analysis of Bonetti et al. (2020, https://doi.org/10.1073/pnas.1911817117), where a non-dimensional index C-I was derived explicitly.

Automated summary

This comment clarifies the misunderstandings in Litwin et al.'s interpretation of the previous works by Bonetti et al., specifically regarding the definition of specific contributing area and the impact of boundary conditions on solutions of the landscape evolution model.