The relative contributions of alpine and subalpine ecosystems to the water balance of a mountainous, headwater catchment

Abstract

Climate change is affecting the hydrology of high‐elevation mountain ecosystems, with implications for ecosystem functioning and water availability to downstream populations. We directly and continuously measured precipitation and evapotranspiration (ET) from both subalpine forest and alpine tundra portions of a single catchment, as well as discharge fluxes at the catchment outlet, to quantify the water balance of a mountainous, headwater catchment in Colorado, USA. Between 2008 and 2012, the water balance closure averaged 90% annually, and the catchment ET was the largest water output at 66% of precipitation. Alpine ET was greatest during the winter, in part because of sublimation from blowing snow, which contributed from 27% to 48% of the alpine, and 6% to 9% of the catchment water balance, respectively. The subalpine ET peaked in summer. Alpine areas generated the majority of the catchment discharge, despite covering only 31% of the catchment area. Although the average annual alpine runoff efficiency (discharge/precipitation; 40%) was greater than the subalpine runoff efficiency (19%), the subalpine runoff efficiency was more sensitive to changes in precipitation. Inter‐annual analysis of the evaporative and dryness indices revealed persistent moisture limitations at the catchment scale, although the alpine alternated between energy‐limited and water‐limited states in wet and dry years. Each ecosystem generally over‐generated discharge relative to that expected from a Budyko‐type model. The alpine and catchment water yields were relatively unaffected by annual meteorological variability, but this interpretation was dependent on the method used to quantify potential ET. Our results indicate that correctly accounting for dissimilar hydrological cycling above and below alpine treeline is critical to quantify the water balance of high‐elevation mountain catchments over periods of meteorological variability. Copyright © 2015 John Wiley & Sons, Ltd.

Assessing Variation in Water Balance Components in Mountainous Inland River Basin Experiencing Climate Change

“…Thompson et al [20] proposed a synthesis framework to compute the water balance from vegetation patterns and catchment scales. Knowles et al [21] estimated the relative contributions of the two ecosystems to the water balance. These reports facilitate our current understanding of the changes of the spatial distribution of water balance components at specific scales.…”

Now You See It Now You Don’t: A Case Study of Ephemeral Snowpacks in the Great Basin U.S.A.

“…Reduction in snow duration can also be caused by the melt of snowpack (Mote, 2006) and losses from sublimation (Harpold et al, 2012;Hood et al, 1999); however, much less is known about the role and distribution of these processes outside of the seasonal snowpack zone. Finally, wind scour can reduce snowpacks by redistributing it to other areas or by increasing blowing wind sublimation (Knowles et al, 2015;Leathers et al, 2004). …”

“…Elevation effects likely a summation of variety of factors, including temperature controls on the rain-snow transition, longwave radiation in cloudy areas, and sensible heat 20 flux. Aspect is often a secondary control on snow distributions because it influences incoming shortwave radiation (Jost et al, 2007;Pomeroy et al, 2003) and wind patterns (Knowles et al, 2015;Leathers et al, 2004;Winstral et al, 2013). Shortwave radiation is the primary driver of ablation via melt and sublimation (Cline, 1997;Marks and Dozier, 1992).…”

Observations and simulations of the seasonal evolution of snowpack cold content and its relation to snowmelt and the snowpack energy budget

“…We employed an additional high alpine station (D1, 3739 m) in the meteorological data infilling procedure (Appendix A), but did not perform model simulations there due to a lack of snow pit validation data. From 2008 to 2012, annual precipitation in the alpine and subalpine averaged 1071 and 752 mm, respectively (Knowles et al, 2015) and the ratio between above-and below-treeline precipitation varies annually as a function of upper-air flow regimes (Kittel et al, 2015). The majority of annual precipitation is snow, with estimates of the proportion of snowfall ranging from 63 to 80 % of total precipitation (Caine, 1996;Knowles et al, 2015).…”

“…From 2008 to 2012, annual precipitation in the alpine and subalpine averaged 1071 and 752 mm, respectively (Knowles et al, 2015) and the ratio between above-and below-treeline precipitation varies annually as a function of upper-air flow regimes (Kittel et al, 2015). The majority of annual precipitation is snow, with estimates of the proportion of snowfall ranging from 63 to 80 % of total precipitation (Caine, 1996;Knowles et al, 2015). Over our study period, December, January, and February mean air temperature was −10.3 • C in the alpine and −6.2 • C in the subalpine.…”