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

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.