by Carolyn J. Browning, Thomas V. Cech, Robert White, and Matthew A. Wilson, Ph.D.
Observed and projected events associated with climate change indicate the need for a paradigm shift from reactive, small-scale, and short-term flood mitigation to proactive, large-scale, and long-term ecosystem adaptation. Adaptation is defined here as “adjustment in natural or human systems in response to actual or expected climatic stimuli or their effects, which moderates harm or exploits beneficial opportunities”.1
Climate Change and Watershed Ecosystems
The Intergovernmental Panel on Climate Change and the U.S. Climate Change Science Program have concluded that climate change will affect water resources in the Intermountain West. Total annual precipitation is increasing in the northern latitudes and average precipitation over the continental United States is increasing as well. However, the Western and Southwestern regions of the United States are trending toward reduced precipitation. In the context of higher temperatures, this reduction in precipitation results in lower soil moisture and a substantial effect of runoff in rivers.1,3 Scientific consensus further suggests that more intense precipitation events are likely to increase in frequency in these regions, thereby increasing flood risk with a high level of statistical confidence (90%).
Natural vegetation cover that is integral to healthy watersheds can be affected by the stresses of climate change noted above. Direct effects can include die-off during drought and blowdown of trees during storm events. In addition, ecological systems, such as fisheries, wetlands, and riparian areas, may be impacted. Indirect climate-sensitive disturbances can include invasive species infestations and wildfire.3 Such effects result in increased vulnerability of watershed ecosystems to long-term stressors.
Studies have further concluded that changes to runoff and streamflow would have considerable regional-scale consequences for economies as well as natural ecosystems.4 The intensity of extreme weather events–droughts, heat waves, floods, and violent storms–could adversely impact regional economic systems, such as ranching, farming, and recreation.
Watershed-Based Planning in the Intermountain West
In the Intermountain West, observed climate-related trends in temperature, snowfall, and streamflow suggest that changes in watershed management practices will be necessary to adapt to the altered hydrologic regime.5 The watershed approach to wetland mitigation6 provides a firm foundation for broadening the analytical lens to include climate-driven variability factors at the watershed scale and to allow for such adaptation. Entire river systems, including upland areas and tributaries throughout the Intermountain West, are becoming dryer and flooding with more intensity.5 Increased drought, coupled with more intense rainfall and flood events, can cause downstream environmental impacts, such as increased sedimentation.
Local flood mitigation activities and river monitoring in the Intermountain West should include consideration of climate change impacts. Observed climate changes create opportunities for a broader view of watershed planning and management activities, including diverting excess flows to downstream reservoirs and groundwater recharge projects in areas like the Lower Arkansas Basin and enlarging existing infrastructure to capture flows produced during intense rain events.
Case Study: Arkansas Headwaters Recreation Area
The Arkansas Headwaters Recreation Area in Colorado encompasses 152 stream miles and more than 4,500 square miles surrounding the Arkansas River from its headwaters in town of Leadville, downstream to the city of Pueblo. The upper river is a regional jewel that provides numerous ecosystem services, including important fisheries and wildlife habitat, water supply, water quality, flood control, and recreation. Competing demands on river basin resources are numerous. Diverse land ownership, past and present mining with associated superfund sites, and agriculture, ranching, and forestry activities make this system complex to manage.
Over the past decade, the area has experienced trends indicative of climatic-related variability throughout the Intermountain West: drought, erosive forces from intense rainfall events, loss of upland vegetative cover, and higher sedimentation rates. However, a lack of baseline data and analysis suggests that additional work is needed to understand the causes and sources of sediment loading and susceptibility to climate-driven variability. Most recently, due to recurring localized flash flood events, the Colorado Division of Parks and Outdoor Recreation initiated a collaborative partnership to lead a pilot stream restoration project at Hecla Junction in the Arkansas Headwaters Recreation Area. This pilot project seeks to apply stream restoration and sediment reduction approaches; monitor physical, chemical, and biological parameters of success; and relate “lessons learned” to other at-risk tributaries in the area. Preliminary results of the restoration project will be compiled after project construction in 2011, thus providing an opportunity to expand the future watershed planning framework to link climate change to local management.
Conclusion and Future Directions
Although impacts of climate change are now being felt across the Intermountain West, a disconnect remains between observed long-term, large-scale trends and flood mitigation activities at the local level. The case study at the Arkansas Headwaters Recreation Area provides a foundation for approaching ecosystem adaption by incorporating climate change variability into local watershed planning and management. A critical next step could be the initiation of a watershed planning process that promotes an approach sensitive to the regional variability driven by climate change.
We gratefully acknowledge this article’s review by our colleagues and experts in the field. We also wish to recognize the efforts of various federal and state land management agencies as well as public and private entities to promote and support watershed protection and climate change adaptation in the upper Arkansas River basin. Contributors include, but are not limited to, the U.S. Environmental Protection Agency, U.S. Department of Interior Bureau of Land Management, U.S. Department of Agriculture Forest Service and Natural Resource Conservation Service, Colorado Department of Public Health and Environment, Colorado Water Conservation Board, Colorado State Parks, and Colorado Division of Wildlife. Contributing members from the Arkansas Headwaters Recreation Area Citizens Task Force include anglers, commercial and river rafting permittees, public representatives, various environmental nonprofit groups, water users, riverfront property owners, local governments, and agricultural members.
1 Intergovernmental Panel on Climate Change. (2007). Summary for policymakers. In M.L. Parry, O.F. Canziani, J.P. Palutikof, P.J. van der Linden, & C.E Hanson (Eds.), Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge, UK, and New York: Cambridge University Press, pp. 7-22.
2 U.S. Interagency Climate Change Adaptation Task Force. (2010). Progress Report of the Interagency Climate Change Adaptation Task Force. Washington, DC.
3 U.S. Climate Change Science Program. (2008). Decision-Support Experiments and Evaluations using Seasonal-to-Interannual Forecasts and Observational Data: A Focus on Water Resources. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Beller-Simms, N., Ingram, H., Feldman, D., Mantua, N., Jacobs, K.L., & Waple, A.M. (Eds.). Asheville, NC: National Oceanic and Atmospheric Administration and National Climatic Data Center, 192 pp.
4 Milly, P.C.D., Dunne, K.A., & Vecchia A.V. (2005). Global pattern of trends in streamflow and water availability in a changing climate. Nature 438(7066), 347-350.
5 Udall, B., & Bates, G. (2007). Climatic and hydologic trends in the Western U.S.: A review of recent peer-review research. Intermountain West Climate Summary, January 2007. Boulder, CO: Western Water Assessment, 1-8.
6 U.S. Army Corps of Engineers and U.S. Environmental Protection Agency. (2008). Final wetland mitigation rule. Federal Register, 73(70)