Future climates are simulated by general circulation models (GCM) using climate change scenarios (IPCC 2014). To project climate change for the sagebrush biome, we used 11 GCMs and two climate change scenarios from the IPCC Fifth Assessment, representative concentration pathways (RCPs) 4.5 and 8.5 (Moss et al. 2010, Van Vuuren et al. 2011). RCP4.5 scenario represents a future where climate policies limit and achieve stabilization of greenhouse gas concentrations to 4.5 W m-2 by 2100. RCP8.5 scenario might be called a business-as-usual scenario, where high emissions of greenhouse gases continue in the absence of climate change policies. The two selected time frames allow comparison of near-term (2020-2050) and longer-term (2070-2100) [...]
Summary
Future climates are simulated by general circulation models (GCM) using climate change scenarios (IPCC 2014). To project climate change for the sagebrush biome, we used 11 GCMs and two climate change scenarios from the IPCC Fifth Assessment, representative concentration pathways (RCPs) 4.5 and 8.5 (Moss et al. 2010, Van Vuuren et al. 2011). RCP4.5 scenario represents a future where climate policies limit and achieve stabilization of greenhouse gas concentrations to 4.5 W m-2 by 2100. RCP8.5 scenario might be called a business-as-usual scenario, where high emissions of greenhouse gases continue in the absence of climate change policies. The two selected time frames allow comparison of near-term (2020-2050) and longer-term (2070-2100) projections relative to the recent past (1980-2010). To evaluate differences across the sagebrush biome, climate projections were evaluated for (1) the biome as a whole and (2) different groupings of ecoregions with similar climate and topography. Over all of the ecoregions examined, average temperatures are projected to increase by about 1 to 3C in the near-term (2020-2050 compared to 1980-2010) under RCP4.5 and RCP8.5. Variability in these near-term temperature changes is primarily a result of different climate models (GCMs) rather than different representative concentration pathways (RCPs). Longer-term (2070-2100) forecasts of average temperature change within these ecoregions vary more substantially, ranging from about 2C to 5C under RCP 4.5 and about 3C to 7C under RCP 8.5. Precipitation is projected to increase slightly across most of the sagebrush biome. However, precipitation is generally more difficult for GCMs to simulate accurately. The projections for precipitation suggest greater uncertainty among GCMs and RCPs than for temperature. In the near-term (2020-2050) biome-wide precipitation change varies among GCMs from a small (less than 10 percent) decrease, to an increase of roughly 20 percent. Longer-term (2070-2100) projections show greater variability, with biome-wide precipitation changes ranging from a 10 percent decrease (about 25 mm yr-1) in the lowest GCM to increases of almost 50 percent (about 150 mm yr-1) in the highest GCM for RCP 8.5.
These changes in precipitation and temperature can influence water cycling and alter the temporal and depth patterns of soil water availability to plants. In particular, warmer temperatures and slightly wetter winters will promote greater moisture availability during winter and early spring, but soils are likely to dry out earlier in the year, creating longer and drier periods of limited moisture availability during the warm season. Geographic patterns identified in projections of climate change illustrate important variations among big sagebrush ecoregions and, thus, sage-grouse habitat types. In particular, the largest increases in spring soil water availability are projected to occur in the high-elevation, mountain big sagebrush and mountain brush areas in the eastern and central portion of the sagebrush biome (Palmquist et al., in review). By contrast, the most dramatic decreases in summer soil moisture are projected in the west-central part of the sagebrush biome. Furthermore, days with wet soil are projected to decrease throughout the range of big sagebrush ecosystems due to temperature related increases in evapotranspiration. These decreases will be especially large in the mid- to high-elevation areas in the northern portion of the biome.
