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Climate Variability, Climate Change, and Large-Scale Ecological Responses: Challenges for Ecosystem Science and Management in the West
Julio L. Betancourt, U.S. Geological Survey, Tuscon, AZ
Two important sources of uncertainty in water planning and ecosystem management in the western U.S. are decadal-to-multidecadal (D2M) natural climate variability and anthropogenic climate change. D2M variability is characteristic of the instrumental record of the past century, as well as tree-ring chronologies of last two millennia. D2M variability can synchronize fluctuations in resource availability within and across regions, and may play a major role in resetting ecosystems at regional scales. Although the tropical Pacific is paramount, D2M variability in the North Atlantic (the so-called Atlantic Multidecadal Oscillation or AMO) and the North Pacific (Pacific Decadal Oscillation) also may play important roles. Resource managers have barely addressed the challenges posed by D2M variability, which makes it that much harder to reckon the impacts of climate change. Abrupt cool season warming beginning 1976-1984, depending on the region, brought on a marked increase in springtime temperatures, an earlier onset of spring by 8 to 10 days, a rise in the elevation at which it rains rather than snows, a decrease in snowpack, earlier snowmelt timing, a shift to an earlier pulse of snowmelt-fed discharge, and an increase in the frequency of large fires A set of nested and downscaled climatological and hydrological models was used recently to attribute many of these changes to the buildup in greenhouse gas emissions, but many questions remain. My presentation will rely on statistical approaches to identify spatiotemporal patterns of temperature, precipitation, and spring onset variations to explore their associations with various modes of large-scale climate variability in the context of climate change. Climatic change compromises a central tenet in water and ecosystem management that natural systems fluctuate within an unchanging and well-defined envelope of variability. These assumptions are embodied to varying degrees in the concepts of Hydrologic Stationarity (HS) and Historic Range of Variation (HRV), and most certainly in the guiding principles of restoration and preservation in environmental and natural resources law. Adaptation to climate change will require retooling traditional methods and developing alternative ones that are better suited for managing and governing resources and ecosystems under a nonstationary climate.
Email: jlbetanc@usgs.gov