| 11 Dec 2025
New insights from fully-integrated surface-subsurface hydrological modeling in high-elevation glaciated environments
Abstract. Recent modeling efforts go towards distributed physics-based modeling for improved hydrological process understanding. The sparse hydro-climatological observations and complex topography in high-elevation mountainous environments have, however, hampered the application of such data-intensive and sophisticated techniques for detailed process exploration. In particular, characterizing surface-subsurface water exchange processes in these terrains remains understudied. Here we implement a fully-integrated and fully-distributed surface-subsurface hydrological model, WaSiM, to quantify the observed streamflow variations and their interactions with groundwater in the high-elevation glaciated environment (Martell Valley) in the central European Alps since the 2000s. Extensive field observations (meteorology, vegetation, glacier mass balance, soil properties, river discharge), especially in-situ groundwater levels, were collected to investigate hydrological processes and constrain model parameters in the surface and subsurface. We observe that in contrast to the delayed responses typically observed in aquifers, shallow alpine groundwater responds nearly as quickly as streamflow to peak snowmelt and extreme rainfall events, highlighting the need for improved subsurface parametrization in hydrological modeling. Surprisingly, we are able to obtain satisfactory model performance when subsurface lateral flow is constrained to zero, indicating its limited influence in river discharge generation at the site and providing new insights into hydrological processes in such an environment. Moreover, to overcome the challenges of integrating point-scale groundwater observations into a fully-distributed hydrological model in high-elevation catchments, we suggest pre-calculating the Topographic Wetness Index to guide piezometer placement. Despite the inherent uncertainties associated with the necessary assumptions of modeling, this study sheds new light on surface-subsurface hydrological processes in high-alpine landscapes.
This study implements a fully-integrated and fully-distributed surface-subsurface hydrological model using the WaSiM framework to examine water exchange processes in the high-elevation, glaciated Martell Valley in the Italian Alps. The authors utilize extensive field data, including rare in-situ high-elevation groundwater level observations—to constrain model parameters across snow, glacier, and subsurface modules
This paper is worthy of publication as it addresses a significant gap in mountain hydrology: the quantification of surface-subsurface interactions in cryosphere-dominated environments. The integration of groundwater level observations into a distributed physics-based model for a high-alpine catchment is a notable technical achievement.
1- While the model achieved satisfactory performance with subsurface lateral flow constrained to zero, this remains a counter-intuitive finding for steep alpine terrains. The authors acknowledge that their piezometers were placed in relatively flat floodplains. The finding might be a localized artifact of piezometer placement rather than a catchment-wide process. More discussion is needed on how this parameterization might affect the model’s ability to simulate hillslope-to-stream connectivity in steeper parts of the catchment.
2- The study notes a specific numerical requirement in WaSiM where the lower boundary of the soil layers must be identical to the lower boundary of the aquifer (calibrated here to 1.30 m). This 1.30 m constraint is quite shallow for an entire catchment. While it may represent the shallow porous aquifers observed, it automatically excludes any simulation of deeper groundwater flow paths. The authors should explicitly clarify if this thickness (1.30 m) is applied uniformly across the entire 77 km2 catchment, including the valley floor where sedimentary deposits are likely much deeper.
3- In Section 6.3, the recommendation to match the TWI spatial resolution to the model resolution (25m×25m) is clear. It might be helpful to include a brief sentence advising how practitioners should handle areas where the 25m grid might smooth over critical local topographic features (like small moraines) mentioned earlier in the text.
4- It would be beneficial to explicitly discuss if this "zero interflow" finding is a physical characteristic of the Martell Valley (e.g., due to high vertical conductivity in porous aquifers) or if it highlights a structural limitation in how current physics-based models distribute lateral flow in steep, shallow-soil alpine terrains. In Section 5.3, consider clarifying if "zero interflow" refers to the model parameter dr being set to 0, and briefly reiterate the physical implication for the reader.
5- As you are working on surface-subsurface hydrological model I do strongly recommend to broad your literature review and cite "Assimilation of sentinel‐based leaf area index for modeling surface‐ground water interactions in irrigation districts"