Agro-ecological class stability decreases in response to climate change projections for the Pacific Northwest, USA

Authors: KAUR, HARSIMRAN - Washington State University; Huggins, David; RUPP, RICHARD - Washington State University; ABATZOGLOU, JOHN - University Of Idaho; STOCKLE, CLAUDIO - Washington State University; REGANOLD, JOHN - Washington State University

Submitted to: Frontiers in Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary: Climate change will impact the viability of different dryland cropping systems of the inland Pacific Northwest. Understanding how the current climate determines where different dryland cropping systems occur can provide insights into how future climate change could influence cropping system distributions across the region. We identified three climatic variables that are very predictive of where different cropping systems currently occur throughout eastern Washington, northern Idaho and northeast Oregon: (1) Holdridge evapotranspiration index; (2) spring precipitation (March, April and May); and (3) precipitation of the warmest four-month season (June, July, August and September). Applying future changes in these climatic variables resulted in significant regional shifts in cropping systems. We found over 50% increases in more dynamic cropping systems that use annual fallow and less occurance of stable cropping systems with annual cropping. These future spatial shifts in cropping systems would result in more use of fallow, a greater hazard for soil erosion, greater cropping system uncertainty, and potentially less cropping system flexibility. These projections are counter to cropping system goals of increasing intensification, diversification, and productivity. These results will be useful for producers, NRCS, Conservation Districts and scientists interested in climate change impacts on cropping systems, soil erosion and overall soil health.

Technical Abstract: Climate change will impact bioclimatic drivers that regulate the geospatial distribution of dryland agro-ecological classes (AECs). Characterizing the geospatial relationship between present AECs and their bioclimatic controls will provide insights into potential future shifts in AECs as climate changes. The major objectives of this study are to quantify empirical relationships between bioclimatic variables and the current geospatial distribution of six dryland AECs of the inland Pacific Northwest of the United States; and apply bioclimatic projections from downscaled climate models to assess geospatial shifts of AECs under current production practices. Two Random Forest variable selection algorithms, VarSelRF and Boruta, were used to identify relevant bioclimatic variables. Three bioclimatic variables were identified by VarSelRF as useful for predictive Random Forest modeling of six AECs: (1) Holdridge evapotranspiration index; (2) spring precipitation (March, April and May); and (3) precipitation of the warmest four-month season (June, July, August and September). Super-imposing future climate scenarios onto current agricultural production systems resulted in significant geospatial shifts in AECs. The Random Forest model projected a 58% and 63% increase in area under dynamic annual crop-fallow-transition (AC-T) and dynamic grain-fallow (GF) AECs, respectively. By contrast, a 46% decrease in area was projected for stable AC-T and dynamic annual crop (AC) AECs across all future time periods for Representative Concentration Pathway 8.5. For the same scenarios, the stable AC and GF AECs showed the least declines in area (8% and 13%, respectively), compared to other AECs. Future spatial shifts from stable to dynamic AECs, particularly to dynamic AC-T and dynamic GF AECs would result in more use of fallow, a greater hazard for soil erosion, greater cropping system uncertainty, and potentially less cropping system flexibility. These projections are counter to cropping system goals of increasing intensification, diversification, and productivity.