Articles | Volume 21, issue 11
Hydrol. Earth Syst. Sci., 21, 5401–5413, 2017
Hydrol. Earth Syst. Sci., 21, 5401–5413, 2017

Research article 01 Nov 2017

Research article | 01 Nov 2017

Field-scale water balance closure in seasonally frozen conditions

Xicai Pan1,2, Warren Helgason3,1, Andrew Ireson4,1, and Howard Wheater1 Xicai Pan et al.
  • 1Global Institute for Water Security, University of Saskatchewan, Saskatoon, SK, Canada
  • 2State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, China
  • 3Civil and Geological Engineering, University of Saskatchewan, Saskatoon, SK, Canada
  • 4School of Environment and Sustainability, University of Saskatchewan, Saskatoon, SK, Canada

Abstract. Hydrological water balance closure is a simple concept, yet in practice it is uncommon to measure every significant term independently in the field. Here we demonstrate the degree to which the field-scale water balance can be closed using only routine field observations in a seasonally frozen prairie pasture field site in Saskatchewan, Canada. 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. In each period, we attempt to quantify the residual between net precipitation (precipitation minus evaporation) and the change in field-scale storage (snow and soil moisture), while accounting for measurement uncertainties. When the residual is negligible, a simple 1-D water balance with no net drainage is adequate. When the residual is non-negligible, we must find additional processes to explain the result. We identify the hydrological fluxes which confound the 1-D water balance assumptions during different periods of the year, notably blowing snow and frozen soil moisture redistribution during the snow accumulation period, and snowmelt runoff and soil drainage during the melt period. Challenges associated with quantifying these processes, as well as uncertainties in the measurable quantities, caution against the common use of water balance residuals to estimate fluxes and constrain models in such a complex environment.

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 on 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.