Integrated assessment of GCM-derived climate change on grain production, water supply and unmanaged ecosystems in the conterminous USA

Twelve climate change scenarios (three GCMs -- BMRC, UIUC and UIUC + Sulfates – each at two levels of global mean temperature (GMT) rise and two levels of CO2-fertilization effectiveness) were applied to the conterminous USA and used to drive the EPIC, HUMUS and BIOME3 models which determine impacts on ,respectively, grain yields, water yields and NPP and geographic distribution of unmanaged ecosystems. Grain production is lower in the scenarios associated with higher global mean temperature. CO2 – fertilization raises production and offsets losses. Because of its great extent, its variable soils, typography and climate, the overall national production of the several crops studied is not greatly affected by the climatic change scenarios used since gains and losses in the different producing regions tend to offset one another, but important differences in regional impacts are noted. Regions most likely to be affected are those on the margins of currently important production zones. Impacts are most consequential in the semi-arid and arid western U.S. Increases and decreases in water supply may be greater than 50% in the Midwest and Southwest. CO2-fertilization leads to a small but significant increase in water yields. One of the more counter-intuitive findings is that total irrigation in the continental US declines under all climate change scenarios studied. In certain regions and scenarios, precipitation declines so much that water supplies are limited and very little cropland can be irrigated; in other scenarios precipitation is so plentiful that irrigation is unnecessary. Drastic decreases in NPP occur in unmanaged ecosystems under the BMRC climates in which the rise in regional temperatures and decrease in precipitation is most extreme. In contrast, the UIUC and UIUC + Sulfate scenarios lead to increases in NPP, especially in the West where precipitation increases most. Agricultural areas that would be abandoned for lack of profitability and those into which it might expand are identified in this study as are the consequences of abandonment and expansion for unmanaged ecosystems.