Work

Balancing subsurface complexity and model simplicity: How much spatially distributed field data is needed to simulate streamflow in a subalpine critical zone

Year: 2026

Type: article

Abstract: Representing subsurface heterogeneity in hydrological models is particularly challenging, as geological and geophysical data are often sparse and infrequent. Hydrologists face two main challenges in subsurface characterization: determining the necessary depth and detail for accurate flow modeling, and developing cost and time-effective methods to capture subsurface heterogeneity. In this study, we conducted preparatory geological and geophysical surveys to investigate subsurface structures and develop conceptual models for the studied catchment. We began with a simple single-layer subsurface model based on initial field investigations and progressively refined it into a more complex three-layer model that incorporates geological, geophysical, and hydraulic properties measured in the field. These conceptual subsurface models were used to inform a 3D hydrological model applied to a 15.28 ha subalpine catchment at Lautaret Pass. Results show that both the three-layer homogeneous and three-layer heterogeneous models perform best, yielding comparable results for runoff (KGEnp = 89, 91), soil moisture (MAPE = 0.23, 0.22), and evapotranspiration (MAPE = 6.65, 6.60). The three-layer model introduces an active regolith layer at an optimal depth, which is responsible for storing and releasing infiltrated water. We argue that conceptual homogeneous models can meet hydrological objectives, provided they are grounded in reliable geological and geophysical field data. However, we also show that the heterogeneous model performs slightly better in capturing snowmelt amplitude, baseflow, evapotranspiration, and surface heterogeneities. These results highlight how cost and time-effective geophysical methods that capture vertical heterogeneity can be leveraged to upscale critical zone processes.

Source: Journal of Hydrology

DOI: 10.1016/j.jhydrol.2026.136455