Midwinter melts in the Canadian prairies: energy balance and hydrological effects

Abstract

Abstract. Snowpack accumulation and depletion are important elements of the hydrological cycle in the Canadian prairies. The surface runoff generated during snowmelt is transformed into streamflow or fills numerous depressions driving the focussed recharge of groundwater in this dry setting. The snowpack in the prairies can undergo several cycles of accumulation and depletion in a winter. The timing of the melt affects the mechanisms of snowpack depletion and their hydrological implications. The effects of midwinter melts were investigated at four instrumented sites in the Canadian prairies. Unlike net radiation-driven snowmelt during spring melt, turbulent sensible heat fluxes were the dominant source of energy inputs for midwinter melt occurring in the period with low solar radiation inputs. Midwinter melt events affect several aspects of hydrological cycle with lower runoff ratios than subsequent spring melt events, due to their role in the timing of the focussed recharge. Remote sensing data have shown that midwinter melt events regularly occur under the present climate throughout the Canadian prairies, indicating applicability of the study findings throughout the region.

Effects of antecedent moisture and macroporosity on infiltration and water flow in frozen soil

“…The field is used as summer pasture, and the maximum soil frost depth measures approximately 0.8-1.0 m (Mohammed, Pavlovskii, Cey, & Hayashi, 2019). The depression from which the soil columns and samples were collected is one of several depressions at the site, two of which (East and West) have been closely monitored as part of a larger study of prairie hydrology, and its hydrologic function is considered representative of other nearby depressions (Mohammed et al, 2019;Pavlovskii, Hayashi, & Itenfisu, 2019). All soil columns, bulk soil, and soil samples were collected from a single topographic depression (designated "East") at the site.…”

“…A heat lamp, concealed within an insulated box, was set on top of each soil column to replicate solar radiation, approximately 250 W m −2 (Pavlovskii, Hayashi, & Itenfisu, 2019), during spring thaw conditions at the field site. The column base was surrounded with insulation, and the entire column assembly was situated above a catchment cylinder used to collect and measure exfiltration from the column.…”

“…Recognizing the overly simplistic models employed for such complex macropore flow systems, the fact that macropore densities bracket the measured values suggests that the rapid flow in the current study likely occurred due to preferential flow in macropores. Midwinter soil freeze-thaw cycles and snowmelt events are a common occurrence throughout many cold regions (Bayard, Stähli, Parriaux, & Flühler, 2005;Pavlovskii, Hayashi, & Itenfisu, 2019;Sutinen, Hänninen, & Venäläinen, 2008) and are expected to increase in frequency and magnitude due to climate change (Henry, 2008). The numbers presented here represent active macropores because research has shown that infiltrating water preferentially migrates through only a fraction of the availability of macroporosity, particularly at greater depths (Cey & Rudolph, 2009;Jarvis, 2007;Nimmo, 2010;Stadler et al, 2000).…”

Quantifying terrain controls on runoff retention and routing in the Northern Prairies

“…Thus, the observed association between depression storage capacity and types of surficial deposits (Figure 4a (Pavlovskii, Hayashi, & Itenfisu, 2019). This implies that the depression storage capacity in areas covered by stagnant ice moraine deposits is sufficient to retain a large fraction of a typical spring runoff volume.…”

“…The variation in depression storage capacity also affects the sensitivity of depression‐focused recharge and runoff routing to the variability in runoff generation. The median depression storage capacity in stagnant ice moraine deposits of 15–26 mm (Figure a) is comparable in magnitude with a long‐term average spring runoff of 22–39 mm observed at a Prairie site in Saskatchewan (Coles, McConkey, & McDonnell, ) and with recently observed snowmelt runoff values of 19.5–21 mm at site 50 km south‐east of the study area (Pavlovskii, Hayashi, & Itenfisu, ). This implies that the depression storage capacity in areas covered by stagnant ice moraine deposits is sufficient to retain a large fraction of a typical spring runoff volume.…”