Publication Date

8-2015

Date of Final Oral Examination (Defense)

5-8-2015

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Hydrologic Sciences

Department

Geosciences

Major Advisor

Kelly Cobourn, Ph.D.

Advisor

Alejandro N. Flores, Ph.D.

Advisor

Jennifer Pierce, Ph.D.

Abstract

As climate changes, the final date of spring snowmelt is projected to occur earlier in the year within the western United States. This earlier snowmelt timing may impact crop yield in snow-dominated watersheds by changing the timing of water delivery to agricultural fields. There is considerable uncertainty about how agricultural impacts of snowmelt timing may vary by region, crop type, and practices like irrigation vs. dryland farming. We utilize parametric regression techniques to isolate the magnitude of impact snowmelt timing has had on historical crop yield independently of climate and physiographic variables that also impact yield. To do this, we examine the historical relationship between snowmelt timing and non-irrigated wheat and barley yield using a multiple linear regression model to predict yield in several Idaho counties as a function of snowmelt date, climate variables (precipitation and growing degree-days), and spatial differences between counties. We apply non-parametric techniques to identify controls on this relationship. To do this, we employ classification and regression trees to predict the relationship between snowmelt timing and yield as a function of both climate and physiographic variables (e.g., elevation). Snowmelt timing significantly predicts crop yield independently of climate variables, which also explain yield. Most trends suggest a decrease in non-irrigated wheat and barley yield with earlier spring snowmelt, but a significant opposite relationship is observed in some Idaho counties. Spring and summer precipitation appears to buffer the negative impact of early snowmelt timing on yield, along with several physiographic characteristics (including elevation/latitude of snowmelt and elevation of planting). These controls may assist agricultural producers, land managers, and water managers in decision making as early snowmelt timing occurs in the future.

Available for download on Sunday, August 27, 2017

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