Climate Change Impacts On Dryland Cropping Systems in the Central Great Plains, USA.

Agricultural systems models are essential tools to assess potential climate change (CC) impacts on crop production and help guide policy decisions.  In this study, impacts of GCM projected CC on dryland crop rotations of wheat-fallow (WF), wheat-corn-fallow (WCF), and wheat-corn-millet (WCM) in the U.S. Central Great Plains (Akron, Colorado) were simulated using the CERES V4.0 crop modules in RZWQM2. The CC scenarios for CO₂, temperature and precipitation were based on a synthesis of IPCC (2007) projections for Colorado. The CC for years 2025, 2050, 2075, and 2100 (CC projection years) was super-imposed on measured baseline climate data for 15-17 years collected during the long-term WF and WCF (1992-2008), and WCM (1994-2008) experiments at the location to provide inter-annual variability.  For all the CC projection years, a decline in simulated wheat yield and an increase in actual transpiration were observed, but compared to the baseline these changes were not significant (p>0.05) in all cases but one. However, corn and proso millet yields in all rotations and projection years declined significantly (p<0.05), which resulted in decreased actual transpiration.  Simulated adaptation via changes in planting dates did not mitigate the yield losses of the crops significantly. Overall, the projected negative effects of rising temperatures on crop production dominated over the positive impacts of atmospheric CO₂ increases in these dryland cropping systems. For comparison, possible effects of historical CO₂ increases during the past century (from 300 to 380 ppm) on crop yields were also simulated using 96 years of measured climate data (1912-2008) at the location. During the period, on average the CO₂ increase enhanced wheat yields by about 30 % with no significant changes in corn yields.