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S. T. Ligare, Center for Watershed Sciences, University of California, Davis, CA, USA.



Whitewater recreation is an aesthetic ecosystem service potentially affected by climate warming alterations to runoff. In California's Sierra Nevada, climate change is likely to reduce water availability with warmer air temperatures and stationary or decreasing precipitation, which will likely alter whitewater recreation opportunities. In this study, we identified 128 whitewater runs on the west slope of the Sierra Nevada within a 13-basin study area that ranged from serene float trips to remote, difficult, kayak expeditions. We used a spatially explicit, one-dimensional rainfall-runoff model to estimate the unregulated hydrology at specific locations within flow thresholds amenable to whitewater recreation. Climate warming scenarios were simulated by increasing air temperature by 2 °C, 4 °C and 6 °C and assuming no change in precipitation.

With mild warming, the average number of boatable weeks per year increases, but more extreme warming decreases the average boatable weeks per year across the Sierra Nevada. Runs in low-elevation drainages, such as the Cosumnes and the Tule River Basins, are most vulnerable to changes in boatable weeks. Yet, high-elevation watersheds, such as the Kern River, also have a large reduction in boatable weeks. Watersheds in the central Sierra Nevada show an increase in boatable weeks. Overall, we found elevation and run type to be the best predictors of resiliency for Sierra Nevada whitewater runs.

Recreation is important for management of rivers, yet it is difficult to quantify and to plan for. This research provides a sensitivity analysis approach to climate warming for the Sierra Nevada and presents a method that can be applied to other regions and whitewater rivers. The observed reduction in whitewater recreation opportunities in unregulated rivers because of climate warming and continued increases in population will likely increase the importance of whitewater boating on regulated rivers and thus the reliance on operations for meeting multiple demands. Copyright © 2011 John Wiley & Sons, Ltd.

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