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Grand Mesa, Uncompahgre and Gunnison National Forest Watershed Vulnerability Assessment, Rocky Mountain Region (R2) areas (Cochetopa, Uncompahgre, and West Elk). The amount of available water is expected to become limiting in the Uncompahgre, Cochetopa, and West Elk geographic areas for three out of four seasons. Figure 19 displays the annual change in aridity indices for both the composite and MIROC_3.2 models, compared to the historic trend. All geographic areas are predicted to become drier. The largest changes will actually occur at the highest elevations (San Juans, Upper Taylor, and Grand Mesa) in those geographic areas with the highest precipitation. These areas also have the greatest capacity to buffer the effects of climate change because of the high levels of water produced from snowmelt and higher occurrence of aquatic habitats. These areas also support high levels of water development for human uses, so any increase in aridity could have a dramatic effect on water uses. This is potentially a very big concern in the Grand Mesa geographic area, where the annual aridity index is predicted to drop below 1. Airidity Index (mm/mm) 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 -­‐11.18% -­‐23.35% Historic COMP MIROC -­‐9.37% 1.29 -­‐18.31% -­‐11.87% 1.07 -­‐22.00% Figure 19. Annual Change in Aridity Index by Geographic Area 0.88 0.87 Geographic areas were ranked for exposure, based on the predicted changes (from the MIROC_3.2 model outputs) for maximum and minimum temperatures and the annual percent change in aridity index (Table 3). A score of 1 indicates lower exposure; a score of 6 indicates higher exposure. Figure 20 displays this ranking. 88 Assessing the Vulnerability of Watersheds to Climate Change -­‐8.72% -­‐9.53% -­‐8.57% -­‐18.05% -­‐18.79% -­‐18.80% San Juans Upper Taylor Grand Mesa West Elk Cochetopa Uncompahgre 0.75 0% -­‐10% -­‐20% -­‐30% -­‐40% -­‐50% -­‐60% -­‐70% -­‐80% -­‐90% -­‐100% Percent Change (%)

Grand Mesa, Uncompahgre and Gunnison National Forest Watershed Vulnerability Assessment, Rocky Mountain Region (R2) Geographic Area Tmin Rank* TMax Rank* Aridity Index Rank* 89 Assessing the Vulnerability of Watersheds to Climate Change Exposure Rank** Exposure Rank (numeric) Uncompahgre 6 6 4 0.89 6 Grand Mesa 5 5 5 0.83 5 San Juans 4 4 6 0.78 4 West Elk 3 3 1 0.39 3 Upper Taylor 2 2 2 0.33 2 Cochetopa 1 1 3 0.28 1 Table 3. Geographic Area Exposure Ranking * Highest number has most change ** (Tmin Rank + Tmax Rank + Aridity Index Rank) / 18 Figure 20. Geographic Area Exposure Ranking Table 4 summarizes key potential climate changes described above and their potential effects to hydrologic process and identified aquatic resource values. This table was modified from Table 2 found in Furniss et al (2010).

Grand Mesa, Uncompahgre and Gunnison National Forest Watershed Vulnerability Assessment, Rocky<br />

Mountain Region (R2)<br />

Geographic Area<br />

Tmin<br />

Rank*<br />

TMax<br />

Rank*<br />

Aridity<br />

Index Rank*<br />

89 Assessing the Vulnerability of Watersheds to Climate Change<br />

Exposure<br />

Rank**<br />

Exposure<br />

Rank<br />

(numeric)<br />

Uncompahgre 6 6 4 0.89 6<br />

Grand Mesa 5 5 5 0.83 5<br />

San Juans 4 4 6 0.78 4<br />

West Elk 3 3 1 0.39 3<br />

Upper Taylor 2 2 2 0.33 2<br />

Cochetopa 1 1 3 0.28 1<br />

Table 3. Geographic Area Exposure Ranking<br />

* Highest number has most change<br />

** (Tmin Rank + Tmax Rank + Aridity Index Rank) / 18<br />

Figure 20. Geographic Area Exposure Ranking<br />

Table 4 summarizes key potential climate changes described above and their potential effects to<br />

hydrologic process and identified aquatic resource values. This table was modified from Table 2<br />

found in Furniss et al (2010).

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