Date of Award:

12-2008

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Civil and Environmental Engineering

Department name when degree awarded

Biological and Irrigation Engineering

Committee Chair(s)

David G. Chandler

Committee

David G. Chandler

Committee

Daniel G. Marks

Committee

Christopher M. U. Neale

Committee

Gary P. Merkley

Committee

David G. Tarboton

Committee

Lawrence E. Hipps

Abstract

This research is focused on understanding the sensitivity of a hydrologic regime at the Reynolds Creek Experimental Watershed (RCEW), a snowmelt dominated semi-arid mountain basin located in southwest Idaho, to climate warming.

Climate data, collected during 1962 to 2006 at many locations in the RCEW, was carefully checked, preprocessed, and corrected for errors and noise signals introduced by the instrument malfunctioning and extreme weather conditions. An Automated Precipitation Correction Program (APCP) was developed to remove mechanical errors from the weighing-recording bucket type precipitation gauge measurements. APCP produces comparable results to the manual techniques but a degree faster (few minutes against 2-3 days) and is not influenced by operator biases.

Long-term climate data collected over a range of elevations of RCEW were analyzed for temporal trends. Significant increase in temperatures, with minimum temperature rising at a faster rate than maximum temperature, was observed at all elevations. Though trends in annual precipitation and streamflow were not significant, streamflow shows a seasonal shift to larger winter and early spring flows, and reduced late-spring and summer flows. These analyses indicate more precipitation as rain than snow, decrease in snow water equivalent (SWE), reduction in number of soil freeze days, and earlier occurrence of plant-water stress. All trends show a significant elevation gradient in either timing or magnitude.

To assess the sensitivity of the mountain snow cover to natural climate variability, and as forced by warming climate, snow cover development and melt during five snow seasons (1984, 1986, 1987, 2001, and 2006) were simulated under actual (base), warm (+2°C), and cold (-2°C) forcing climate scenarios, at the Reynolds Mountain East (RME) basin, a head water catchment of the RCEW. Selected seasons displayed tremendous variability in snow distribution, accumulation, and melt with snowcover during dry snow (1987, 2001) seasons substantially smaller, and peak snow accumulations and melts about a month earlier compared to wet snow seasons (1984, 1986, 2006). Results from altered climate scenario simulations show that colder conditions result in less rain and more snow, increase in SWE, later timing of peak SWE, and later snowmelt. The simulations with warm scenarios show more rain and less snow, decrease in SWE, earlier timing of peak SWE, and earlier timing of snowmelt. In general, seasonal snowcover shows greater sensitivity to warm scenarios than cold.

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