Percent change in mean annual precipitation between 1971-2000 and 2070-2099 under Hadley A2 for the Apache-Sitgreaves study area, Arizona, USA

This map represents the percent change in average annual precipitation, simulated by the model MC1 between the 30-year periods 1971-2000 and 2070-2099 under the Hadley climate change and A2 emissions scenarios.  The average annual precipitation for the respective 30-year periods decreased in all of the 5,311 grid cells of the Apache-Sitgreaves study area. The greatest decrease was -25.1%; the least decrease was -9.2%; and the mean decrease was -15.8%

The vegetation model MC1 (e.g. Bachelet et al. 2001) was used to simulate vegetation dynamics, associated carbon and nitrogen cycle, water budget, and wild fire impacts at two study sites in eastern Oregon (Deschutes and Fremont-Winema National Forests) and in Arizona (Apache Sitgreaves National Forest area) in the context of a project funded by the USDA Forest Service (PNW 09-JV-11261900-003). Historical climate input data used to run the model were provided by the PRISM group (Chris Daly, OSU) at a 30arc second (800m) spatial grain. The model was also run using future climate change projections from various general circulation models including Hadley, CSIRO Mk3 and MIROC 3.2 medres. Future climate change climate datasets were generated through statistical downscaling from general circulation model output using a simple anomaly method and the climatology (1971-2000) from the PRISM group at 30arc second spatial grain.  The model was run assuming that nitrogen demand from the plants was always met so that the nitrogen concentrations in various plant parts never dropped below their minimum reported values. A CO2 enhancement effect increased productivity and water use efficiency as the atmospheric CO2 concentration increased.