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Grand Mesa, Uncompahgre and Gunnison National Forest Watershed Vulnerability Assessment, Rocky Mountain Region (R2) Season Precipitation (%) Temperature (˚C) Temperature (˚F) Annual -10.0 +3.0 +5.4 Winter ~0.0 +3.0 +5.4 Spring -15.0 +3.0 +5.4 Summer -20.0 +4.0 +7.0 Fall -10.0 +3.0 +5.4 Table 2. Temperature and Precipitation Changes for “More Extreme” Climate Change Scenario developed by Barsugli and Mearns for the Gunnison Basin Predicted changes under the “more extreme” scenario include: 1. Increase in annual temperatures of 3 ˚C (5.4 ˚F). 2. A 10% decrease in annual precipitation, with greater decreases in warm season precipitation. 3. Decrease in precipitation and increase in temperature, both act to reduce annual stream flow totals in the range of 20% to 25%. 4. Warming temperatures lead to a later accumulation of snow in the fall and earlier snowmelt in the spring. Because this likely represents a hot/dry scenario for much of the west, the potential exists for more frequent dust deposition events, which also may lead to an earlier melt and to reduced water yield from the snowpack. 5. Snowmelt-driven stream flow will peak about two or more weeks earlier in the spring, though this effect may be less if dust effects on snowmelt are strong. The combined effects of dust and temperature on snowmelt timing tend to be dominated by the dust effects. 6. The much earlier melt, along with decreased summer precipitation and increased summer temperatures, will result in extremely low amounts of water stored in the soils during summer and fall. VIC Model Climate Change Predictions The primary predictive model used to display climate changes was the VIC hydrologic model. Data derived using the VIC model were available from the Climate Impacts Group (CIG) at the University of Washington. Historic trends were developed from the climate record from 1916 to 2006. Future prediction results for temperature- and precipitation-related parameters were generated using: 1) a composite of the 10 climate models that best resembled the historic trend, 2) the MIROC_3.2 model (more extreme temperature increases), and 3) the PCM1 model (less extreme temperatures increases) for two time periods (2030-2059 and 2070-2099) using the A1B emissions scenario. Data were available at the ~6 km-grid scale for monthly averages for 21 parameters for each model, but not all parameters were reviewed by the GMUG team. (Data downloaded from ftp://ftp.hydro.washington.edu/pub/climate/USFS_monthly_summaries/CO/ on 11/5/2010). In addition, some of the data were summarized at the HUC-5 scale. (Data downloaded from ftp://ftp2.fs.fed.us/incoming/gis/PNF/WVA/ on 10/22/2010). Outputs obtained from the VIC Model data are described below. 84 Assessing the Vulnerability of Watersheds to Climate Change
Grand Mesa, Uncompahgre and Gunnison National Forest Watershed Vulnerability Assessment, Rocky Mountain Region (R2) Initially, we reviewed the HUC-5 data for the composite, and MIROC_3.2 models, comparing projections of historic condition with two time periods (2030-2059 and 2070-2099) for the following parameters: • precipitation (monthly total, seasonal* total) • tmax (daily maximum temperature monthly average, seasonal* average) • tmin (daily minimum temperature monthly average, seasonal* average) • runoff (monthly total, seasonal* total) • baseflow (monthly total, seasonal* total) • hydrograph (runoff + baseflow as monthly total, seasonal* total) *Seasonal breakdown: winter = December, January, February; spring = March, April, May; summer = June, July, August; fall = September, October, November Charts for each HUC-5 were created to compare the composite and MIROC_3.2 model results to the historic trend for these parameters (this information is available as GMUG Appendix A at www.fs.fed.us/ccrc/wva/appendixes). (Note: We did not chart the PCM1model results that averaged between the composite and MIROC_3.2 results). For most HUC-5 watersheds, the data display future decreases in summer and fall precipitation and shifts in precipitation between winter and spring. Temperature increases of 2 to 3 ˚C are predicted for both maximum and minimum temperatures throughout the year. Runoff periods are predicted to shift one to two months earlier and total runoff is reduced. (Note: these predictions are in addition to the changes already seen since 1978, described earlier.) Because some HUC-5 watersheds include a wide range of elevations (ranges of 5,000 to 7,000 feet), we also reviewed the 6 km-grid scale VIC data. Predicted results for the composite and MIROC_3.2 models were compared to the historic trend for the same parameters listed above, as well as for evapotranspiration. We looked at the actual change between modeled and historic results, and the percent change on a monthly basis at the 6 km-grid scale. Maps showing monthly results at the grid scale display large differences between higher and lower elevation areas (see this information is available as GMUG Appendix B at www.fs.fed.us/ccrc/wva/appendixes). We used the six geographic areas (areas with similar climatic regimes and elevation ranges) to examine predicted climate changes (see Figure 4). Since most of the lower elevations within the HUC-5 scale watersheds are actually below the GMUG Forest boundary, reviewing exposure parameters at the geographic area scale is more representative for the GMUG. We chose to focus on a smaller subset of VIC parameters at the geographic area scale. We compared the predicted seasonal temperature changes (both maximum and minimum averages) from the MIROC_3.2 model to the historic model. Figure 16 displays the seasonal increase in maximum average temperature by geographic area. Figure 17 displays the seasonal increase in minimum average temperature by geographic area. 85 Assessing the Vulnerability of Watersheds to Climate Change
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AUTHORS AND CONTRIBUTORS Authors* M
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ASSESSSING THE VULNERABILITY OF WAT
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staff; the task group included repr
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Figure 2. Conceptual model for asse
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Figure 3. Density of springs and sm
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Using Historic Data One finding con
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NF (Region 8) relied on information
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level of uncertainty. Though there
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climate (Casola et al. 2005). Only
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sensitivity. Most were derived from
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The sensitivity evaluation typicall
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in exposure. The result of combinin
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highest priority for management act
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to information affected the assessm
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with and rely on in many resource d
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Pilot National Forest Reports Conte
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Assessment of Watershed Vulnerabili
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Gallatin National Forest Watershed
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Coconino National Forest Watershed
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Sawtooth National Forest Watershed
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Ouachita National Forest Watershed
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Chugach National Forest Watershed V
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