On the accurate simulation of hydrological droughts in Alpine regions: investigating the multiple role of rainfall-runoff model dynamics and basin characteristics

The reliability of rainfall-runoff models in reproducing hydrological drought events is of primary importance for multiple applications (e.g. water resource management or agricultural risk assessment), especially in a context of expected future water scarcity. Typical model performance metrics are often not enough to assess the accuracy in the simulation of droughts. In fact, it is necessary to consider drought-specific indices taking into account, e.g., low flow characteristics, duration and deficit volumes as well as their seasonality and timing. Understanding which hydrological processes are (or are not) adequately modeled and why, in respect to such drought-specific performances, allows to assess the strengths and weaknesses of each model and may provide guidance on how to improve model set-up and its reliability.

Through the application of a conceptual semi-distributed model on a set of Alpine basins, the aim of this preliminary work is to analyse the relationship between drought-specific performance metrics, basin characteristics and model parameters. In particular, the specific influence of the different model state variables (e.g. snow water equivalent, evapotranspiration and soil moisture) on the reproduction of drought events is investigated.

The model used is a semi-distributed modelling framework based on the airGR rainfall-runoff models (Coron et al. 2017), applied through the R package airGRiwr (Dorchies 2022). The case study is a set of Alpine catchments, characterised by a high degree of “nestdness” which allows to fully implement the semi-distributed model structure and to perform its diagnosis.

The major advantage of a semi-distributed model, if properly set-up, is its ability to differentiate hydrological dynamics between the sub-catchments. In mountainous basins, for instance, simulating in a separate way the upstream headwater sub-catchments may substantially improve the accuracy in the simulation of snow storage and melting, which strongly affect the occurrence and timing of drought events. For this reason, the work will also analyse the benefits of an increasing spatial resolution of the semi-distributed set-up of the model, comparing the outcomes obtained when sequentially calibrating the model in a semi-distributed fashion on the upstream sub-catchments in respect to the baseline of a lumped configuration.

 

References

Coron, L., Thirel, G., Delaigue, O., Perrin, C. and Andréassian, V. (2017). The Suite of Lumped GR Hydrological Models in an R package. Environmental Modelling and Software, 94, 166-171, doi: 10.1016/j.envsoft.2017.05.002.

David Dorchies (2022). airGRiwrm: 'airGR' Integrated Water Resource Management. R package version 0.6.1. https://CRAN.R-project.org/package=airGRiwrm