Preprints
https://doi.org/10.5194/hess-2021-362
https://doi.org/10.5194/hess-2021-362

  13 Jul 2021

13 Jul 2021

Review status: this preprint is currently under review for the journal HESS.

Stream discharge depends more on the temporal distribution of water inputs than on yearly snowfall fractions for a headwater catchment at the rain-snow transition zone

Leonie Kiewiet1,2, Ernesto Trujillo3,4, Andrew Hedrick4, Scott Havens4, Katherine Hale5, Mark Seyfried4, Stephanie Kampf1, and Sarah E. Godsey2 Leonie Kiewiet et al.
  • 1Department of Ecosystem Science and Sustainability, Colorado State University, Fort Collins, CO, USA
  • 2Department of Geosciences, Idaho State University, Pocatello, ID, USA
  • 3Department of Geosciences, Boise State University, Boise, ID, USA
  • 4USDA Agricultural Research Service, Boise, ID, USA
  • 5Department of Geography, University of Colorado, Boulder, CO, USA

Abstract. Climate warming affects snowfall fractions and snowpack storage, displaces the rain-snow transition zone towards higher elevations, and impacts discharge timing and magnitude as well as low-flow patterns. However, it remains unknown how variations in the spatial and temporal distribution of precipitation at the rain-snow transition zone affect discharge. To investigate this, we used observations from eleven weather stations and snow depths measured in one aerial lidar survey to force a spatially distributed snowpack model (iSnobal/Automated Water Supply Model) in a semi-arid, 1.8 km2 headwater catchment at the rain-snow transition zone. We focused on surface water inputs (SWI; the summation of rainfall and snowmelt) for four years with contrasting climatological conditions (wet, dry, rainy and snowy) and compared simulated SWI to measured discharge. We obtained a strong spatial agreement between snow depth from the lidar survey and model (r2: 0.88), and a median Nash-Sutcliffe Efficiency (NSE) of 0.65 for simulated and measured snow depths for all modelled years (0.75 for normalized snow depths). The spatial pattern of SWI was consistent between the four years, with north-facing slopes producing 1.09 to 1.25 times more SWI than south-facing slopes, and snow drifts producing up to six times more SWI than the catchment average. We found that discharge in a snowy year was almost twice as high as in a rainy year, despite similar SWI. However, years with a lower snowfall fraction did not always have lower annual discharge nor earlier stream drying. Instead, we found that the dry-out date at the catchment outlet was positively correlated to the snowpack melt-out date. These results highlight the heterogeneity of SWI at the rain-snow transition zone and emphasize the need for spatially distributed modelling or monitoring of both the snowpack and rainfall.

Leonie Kiewiet et al.

Status: open (until 07 Sep 2021)

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Leonie Kiewiet et al.

Leonie Kiewiet et al.

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Short summary
Mountainous regions are receiving more rain and less snow due to climate change. We investigated how that change affects stream discharge in a region that already receives a mix of rain and snow, by simulating rainfall and snowmelt for four contrasting years. We found that stream discharge depended more on the temporal distribution of precipitation than on yearly snowfall fractions. This highlights the importance of distributed modelling of rainfall and snowmelt in headwater-scale studies.