Constraining the HBV model for robust water balance assessments in a cold climate

Helene Birkelund Erlandsen,Hege Hisdal,Stephanie Eisner,Lena Merete Tallaksen,Stein Beldring,Shaochun Huang

doi:10.2166/nh.2021.132

Abstract

Abstract Robust projections of changes in the hydrological cycle in a non-stationary climate rely on trustworthy estimates of the water balance elements. Additional drivers than precipitation and temperature, namely wind, radiation, and humidity are known to have a significant influence on processes such as evaporation, snow accumulation, and snow-melt. A gridded version of the rainfall-runoff HBV model is run at a 1 × 1 km scale for mainland Norway for the period 1980–2014, with the following alterations: (i) the implementation of a physically based evaporation scheme; (ii) a net radiation-restricted degree-day factor for snow-melt, and (iii) a diagnostic precipitation phase threshold based on temperature and humidity. The combination of improved forcing data and model alterations allowed for a regional calibration with fewer calibrated parameters. Concurrently, modeled discharge showed equally good or better validation results than previous gridded model versions constructed for the same domain; and discharge trend patterns, snow water equivalent, and potential evaporation compared fairly to observations. Compared with previous studies, lower precipitation and evaporation values for mainland Norway were found. The results suggest that a more robust and more physically based model for climate change studies has been obtained, although additional studies will be needed to further constrain evaporation estimates.

Highlights

Many hydrological models were developed for operational water resources management and have been built to rely only on input data that is commonly available, and to be easy to use
Numerically solving the surface energy balance requires an increase in input data requiring higher storage and pre-processing capacity, as well as an increase in model integration time; it allows the computation of surface temperature, and imposing a closed surface energy balance, which further constrains the latent heat flux or evaporation estimates
Six soil parameters are routinely calibrated: field capacity (FC), an exponent controlling the fraction of infiltration that percolates to the upper zone, a parameter controlling the percolation to the lower zone, the upper and lower zones’ runoff response coefficients, and the upper zone recession parameter

Summary

Introduction

Many hydrological models were developed for operational water resources management and have been built to rely only on input data that is commonly available, and to be easy to use. The non-stationarity of the current climate calls for hydrological models with a stronger physical basis and a higher robustness in a wide range of climates (Ferguson ; Clark et al ). Hydrological models range from the simplest, datadriven, lumped, and conceptually based water balance models, to those akin to land surface models, where the surface energy balance is solved numerically (see e.g. Kauffeldt et al ). Numerically solving the surface energy balance requires an increase in input data requiring higher storage and pre-processing capacity, as well as an increase in model integration time; it allows the computation of surface temperature, and imposing a closed surface energy balance, which further constrains the latent heat flux or evaporation estimates. The term evaporation encompasses water loss from soil, leaves, lakes, and plant stomata (transpiration)

Methods

Discussion

Conclusion