CLIMATE CHANGE IMPACTS AND MITIGATION ON WHEAT SYSTEM IN PACIFIC NORTHWEST
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Although the world’s food demand is projected to increase due to population growth, the future of the global food supply is not well understood given the complex nature of stressors such as climate change. The goal of this dissertation is to improve our understanding of the impact of climate change on wheat-based dryland agriculture in the inland U.S. Pacific Northwest (PNW). We address the following three specific objectives: (i) Investigate how dryland wheat production in the PNW responds to future climate conditions and how would environmental conditions for wheat change in the future. (ii) Understand how climate change affects possible shifts between the historical borders of different agro-ecological areas and associated cropping systems in the drylands of the PNW. (iii) Evaluate the impact of climate change on greenhouse gas emissions (GHG) and components of the soil nitrogen and carbon budgets. A regional assessment was conducted using a cropping systems simulation model (CropSyst) and daily weather data (4x4 km grid) downloaded from twelve general circulation model (GCMs) climate projections for two representative concentration pathways of atmospheric CO2 (RCP 4.5 and RCP 8.5). The results presented include projections for a baseline historical period (1980–2010) and future periods 2015-45 (2030s), 2035-65 (2050s) and 2055-85(2070s). The study region was divided into three agro-ecological zones (AEZs): grain fallow, grain fallow transition, and continuous cropping. The following rotations were included: WW–SF, WW–SW–SF, and WW–SW–SP, where WW is winter wheat, SW is spring wheat, SP is spring peas, and SF is summer fallow. A reduced conservational tillage practices in each AEZ was evaluated. The results indicated that regional dryland wheat production will increase in the future, but with spatial variation and uncertainty related to future weather projections. Improvement in yield will provide opportunities for intensification of cropping systems and may lead to some reduction of fallow use. Total GHG emissions (nitrous oxide and carbon dioxide from reduced SOC stocks) had a decreasing trend while N2O emissions accounted for a larger portion of total GHG and the relative contribution had an increasing trend toward the 2070s since SOC losses were lower.