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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
16 Jun 2016
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Hydrology and Earth System Sciences (HESS) and is expected to appear here in due course.
Field-scale water balance closure in seasonally frozen conditions
X. Pan1, W. Helgason2,1, A. Ireson3,1, and H. Wheater1 1Global Institute for Water Security, University of Saskatchewan, Saskatoon, SK, Canada
2Civil and Geological Engineering, University of Saskatchewan, Saskatoon, SK, Canada
3School of Environment and Sustainability, University of Saskatchewan, Saskatoon, SK, Canada
Abstract. Hydrological water balance closure is a simple concept, yet in practice it is usually impossible to measure every significant term independently in the field. Here we explore field scale water balance closure in a prairie pasture field site in Saskatchewan, Canada. The area is cold, flat and semi-arid, with snowmelt-dominated runoff. Arrays of snow and soil moisture measurements were combined with a precipitation gauge and flux tower evapotranspiration estimates. We consider three hydrologically distinct periods: the snow accumulation period over the winter, the snowmelt period in spring, and the summer growing season. Over two years studied (1 November 2012 to 31 October 2014), we saw similar snowpacks develop each winter result in markedly different runoff responses during melt. This was attributed to different soil moisture conditions prior to the snow accumulation period in each year. In the more typical year (2013), the snow pack mostly infiltrates into the soil, and the water balance is dominated by vertical land-atmosphere exchanges. However, in the wetter year (2013–2014), the snowpack was not absorbed as soil moisture, and significant losses (i.e. deep or lateral fluxes) occurred in response to rainfall in the early growing season. As a result, we were unable to close the water balance. In particular, we were unable to quantify how the excess melt water was partitioned between lateral runoff and vertical soil drainage leading to groundwater recharge. Shallow piezometers suggest groundwater recharge was significant in the wet year, and was depression focused. It is concluded that models which use physically-based process representations to partition the melt cannot be rigorously validated using conventional field-scale measurements based on water balance residuals. Rather, models should be constrained using direct observations, accounting for uncertainty, and there is a need to establish which observations (what, where and when) are most effective at constraining the uncertainties in the water balance components.

Citation: Pan, X., Helgason, W., Ireson, A., and Wheater, H.: Field-scale water balance closure in seasonally frozen conditions, Hydrol. Earth Syst. Sci. Discuss.,, in review, 2016.
X. Pan et al.
X. Pan et al.
X. Pan et al.


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Short summary
In this paper we present a case study from a heterogeneous pasture site in the Canadian prairies, where we have quantified the various components of the water balance at the field scale, and critically examine some of the simplifying assumptions which are often invoked when applying water budget approaches in applied hydrology. We highlight challenges caused by lateral fluxes of blowing snow and ambiguous partitioning of snow melt water into runoff and infiltration.
In this paper we present a case study from a heterogeneous pasture site in the Canadian...