Impacts of Increased over-Winter Precipitation on Dryland Cereal Production Systems in the Pacific Northwest.

Climate change adaptation in agriculture will require a thorough understanding of field scale climate induced changes to nutrient transport and soil water storage and erosion. We must further understand how climate change may impact annual farm management decisions and the coupled effect this will have on the soil and nutrient transport. Across the cereal grain production region of the inland Pacific Northwest, referred to here as the Regional Approaches to Climate Change (REACCH), climate and soil variability result in dramatic differences in the type and intensity of crop production.  Future climate projections suggest a slight decline in summer precipitation and an increase in winter precipitation in the REACCH region. The increase in winter precipitation in the crop-fallow transition zone (300-500 mm/yr precipitation) may allow growers to convert to annual cropping, while growers in wetter regions (> 500 mm/yr) may need to rely on more fall-seeded crops to avoid delayed spring planting.  In Pullman WA, located in the high precipitation annual cropping zone, climate models predict an increase in winter precipitation of 75 mm and a decline of 7 mm during summer months by the latter half of the 21^st century. The predicted change in seasonal precipitation may have significant implications on the future management of cropping systems, soil water storage and erosion, and nitrate export in the region. At the field scale, complex topography, soil development, and historically high soil erosion has led to extreme variability in water storage and crop yield.  Over the last 10 years more growers are transitioning to variable rate fertilizer application strategies to minimize nitrogen losses.  Using spatially distributed biophysical models we examine the spatial and temporal impact of future climate scenarios and associated farm management adaptations on soil water storage and nitrate export in the high precipitation zone of the REACCH region.