Comparison of agricultural impacts of climate change calculated from high and low resolution climate change scenarios: Part I. The uncertainty due tospatial scale

We investigated the effect of two different spatial scales of climate chang e scenarios on crop yields simulated by the EPIC crop model for corn, soybe an, and wheat, in the central Great Plains of the United States. The effect of climate change alone was investigated in Part I. In Part II (Easterling et al., 2001) we considered the effects of CO2 fertilization effects and a daptation in addition to climate change. The scenarios were formed from fiv e years of control and 2 x CO2 runs of a high resolution regional climate m odel (RegCM) and the same from an Australian coarse resolution general circ ulation model (GCM), which provided the initial and lateral boundary condit ions for the regional model runs. We also investigated the effect of two di fferent spatial resolutions of soil input parameters to the crop models. We found that for corn and soybean in the eastern part of the study area, sig nificantly different mean yield changes were calculated depending on the sc enario used. Changes in simulated dryland wheat yields in the western areas were very similar, regardless of the scale of the scenario. The spatial sc ale of soils had a strong effect on the spatial variance and pattern of yie lds across the study area, but less effect on the mean aggregated yields. W e investigated what aspects of the differences in the scenarios were most i mportant for explaining the different simulated yield responses. For instan ce, precipitation changes in June were most important for corn and soybean in the eastern CSIRO grid boxes. We establish the spatial scale of climate change scenarios as an important uncertainty for climate change impacts ana lysis.