Date of Final Oral Examination (Defense)

8-2009

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Hydrologic Sciences

Department

Geosciences

Major Advisor

James P. McNamara, PhD

Abstract

Increasing populations, rapid land use changes, and climate change in mountainous areas have stressed water resources and reduced available water from snowpacks. In anticipation of warmer temperatures, receding snowlines, and increasing water demands, water managers will need detailed snowmelt energy and water balance information from the margin as transitional snow replaces deeper snowpacks. Patchy shallow snow, found at transitional snow elevations, has a distinct energy balance that includes local advection and short wave radiation penetration of snow less than 10 cm deep. Solar penetration to the soil surface provides a heat source that can be absorbed by the soil and conducted back to the snow. The objective of this study is to compare ground heat flux beneath snow less than 10 cm depth (shallow) and greater than 10 cm depth to see if solar penetration of shallow snow results in the heating of soils and an increased ground heat flux. Further objectives of the study are to evaluate the mathematical model for ground heat flux and to assess distributed temperature sensing (DTS) as a tool for measuring soil/snow interface temperatures beneath spatially unpredictable shallow snow extents.

To capture and quantify the additional energy flux below patches of spatially unpredictable shallow snow, near surface soil temperatures must be taken at large spatial scales. High spatial resolution DTS was deployed prior to snow season, 2.5 cm beneath the soil surface throughout a mid-elevation semi-arid watershed, to capture near surface soil temperatures below spatially unpredictable patchy snow. Ground heat flux was modeled from the soil temperatures.

The soil column in this study showed an increasing modeled ground heat flux as soil temperature measurement moved closer to the soil-snow interface. This trend violates the steady state assumption of the model with respect to the soil column and reveals that soil temperature measurement depth has a substantial inverse relationship with the magnitude of modeled ground heat flux.

The DTS was successful in capturing soil temperatures beneath the unpredictable snow patches. However, due to DTS spatial averaging along the cable to produce point measurements, temperature accuracy was compromised. Despite the possible accuracy of ±0.04°C, this compromise lead to uncertainties in heat sources responsible for soil temperature differences beneath shallow and deep snow.

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