THE INFLUENCE OF PRECIPITATION PHASE ON HYDROGRAPH FORM

The diversity of topographic and climatic characteristics in mountainous catchments drives heterogeneity in hydrologic processes and inhibits the progression of hydrologic sciences for several reasons. First, unrecognized heterogeneity introduces noise into hydrologic scaling relationships. Second, heterogeneity complicates hydrologic modeling and subsequent prediction of the impacts of climate change on water resources. Third, heterogeneity limits the applicability of generalized techniques of water resource management. In efforts to advance the science beyond some of these dilemmas we have implemented a hydrologic monitoring network that spans a large elevation and spatial gradient in the Salmon River basin, central Idaho. We attempt to answer the question: what is the influence of precipitation phase on hydrograph form? We used hypsometry to identify basins that are contained entirely within distinct elevation zones: low (400 – 1800 m), mid (1000 – 2200 m) and high (2200 – 3200 m). We hypothesize that these zones are dominated by, liquid, mixed phase and solid precipitation, respectively. We have monitored two years of spring snowmelt runoff and results thus far suggest that all monitored catchments exhibit snow influence. However, low elevation catchments are characterized by short duration, low magnitude snowmelt runoff events, tending to have an overall flashier nature, especially during winter months. Mid elevation catchments exhibit a greater snow influence, reflected in longer duration, higher magnitude snow melt events and reflect the input of mixed-phase precipitation with occasional liquid precipitation events during winter months. High elevation catchments are characterized by the longest duration, highest magnitude snow melt runoff and have uneventful baseflow hydrographs during winter months, reflecting the active construction of a snow reservoir. Our work demonstrates that the magnitude, frequency and duration of hydrologic events vary with time and intensity across a landscape. We argue that hydrologic and metrological networks that are designed to document the variability in hydrologic processes across elevation and orographic gradients will be the most valuable for advancing the science and methods of water resources management in the midst of a warming climate.