Simulation of Regional Yields and GHG Emissions Under Climate Change of Wheat-Based Systems in the US Pacific Northwest.

As part of the Regional Approaches to Climate Change (REACCH) project (funded by USDA-NIFA), a regional assessment of historical and future yields and greenhouse gas (GHG) emissions of wheat-based cropping systems in the US Pacific Northwest is being conducted. This computer simulation-based assessment is being done using the CropSyst cropping systems simulation model and daily weather data downscaled to a 4x4 km grid. Future weather is projected using 14 general circulation models (GCMs) and two representative concentration pathways of future atmospheric CO₂ (rcp 4.5 and rcp 8.5). The study region is divided in 4 agro-ecological zones (AEZ): low, intermediate and high precipitation zones and irrigated zone. A typical conventional tillage (CT) cropping system in each AEZ is evaluated as a baseline, with alternative cropping systems being considered later in the project. The results presented include projections for the periods 2015-44 (2030s) and 2035-64 (2050s). Overall, the mean of all GCMs indicates a trend to a small increase in winter wheat yields by half of the century, but with large variability among GCMs. GHG emissions, represented by changes in soil organic carbon and N₂O emissions, are projected to increase slightly due to enhanced soil carbon losses due to warming, with N₂O losses decreasing slightly due to some increase in crop N uptake while fertilization application is kept invariant.