Impacts of Climate Variability and Change, Pacific Northwest

Experience of the recent past illustrates the impacts that the climate variations have on the Pacific Northwest, and illustrates that there are both winners and loser when the climate is different from the "average."The mild winter and spring of 1997-98 saw an early snow melt, which strained regional water supplies during the summer and fall months.An especially warm and dry summer, coupled with the early melt, led to exceptionally low flows and high temperatures in many Northwest streams.These conditions in turn caused sever difficulties for salmon.However, 1997-98 also had benefits for the region, which avoided the damage and disruption caused by heavy snow fall and winter flooding during the previous two winters.Climate is not a constant, and yet many aspects of human infrastructure and activities are planned with the assumption that it is constant.But what happens when climate produces a surprise?What if, furthermore, there are long-term changes in climate?Humans have altered the composition of Earth's atmosphere to such an extent that climate itself appears to be changing.The consequences of a changing climate may be beneficial for some places and activities, and detrimental for others.This report describes the possible impacts of human-induced climate change and of natural climate variability like El Niño, focusing on the water resources, salmon, forests, and coasts of the Pacific Northwest (PNW).It has been prepared largely by the Climate Impacts Group (CIG) at the University of Washington.The CIG, under the direction of Professor Edward L. Miles, is an interdisciplinary group of researchers from the physical, biological, and social sciences working together to understand the impacts of climate variability and change on the Northwest.Looking at the recent past, much of the climate history of the PNW can be described by a few recurring patterns.The strongest pattern highlights the tendency for winter climate to be either relatively cool and wet or relatively warm and dry.Cool-wet winters are generally associated with increased risks of flooding and landslides, abundant summer water supply, more abundant salmon, reduced risk of forest fires, and improved tree growth (except at high elevation).Warm-dry winters are often followed by summer water shortages, less abundant salmon, and increased risk of forest fires.The occurrence of the cool-wet or warm-dry winter pattern is influenced by two main climate variations in the Pacific Basin: ENSO (El Niño-Southern Oscillation) primarily on year-to-year timescales and PDO (the Pacific Decadal oscillation) primarily on decade-to-decade timescales.ENSO and PDO cause variation sin snowpack and streamflow, and hence the ability to meet water resource objectives; with respect tot he region's water resources, ENSO and PDO can reinforce or cancel each other.In contrast, the response of forests and salmon is correlated more strongly with the PDO than with ENSO.The magnitude of seasonal anomalies of temperature and precipitation leading to the above effects is strikingly small, but these past anomalies enable us to calibrate the possible responses to long-term climate change.Looking to the future, computer models of climate generally agree that the PNW will become, over the next half century, gradually warmer and wetter, with most of the precipitation increase in winter.These trends mostly agree with observed changes over the past century.Wetter winters would likely mean more flooding of certain rivers, and landslides on steep coastal bluffs.The region's warm, dry summers may see slight increases in rainfall, according tot he models, but the gains in rainfall will be more than offset by losses due to increases in evaporation.Loss of moderate-elevation snowpack in response to warmer winter temperatures would have enormous and mostly negative impacts on the region's water resources, forests, and salmon.Among these impacts are a diminished ability to store water in reservoirs for summer use, more drought-stressed tress leading to reductions in forested area, and spawning and rearing difficulties for salmon.Knowing what changes might occur is only part of the challenge, however.This knowledge must make its way from the realm of research to the realm of decisions, and be used in decisions.Large practical and, in some cases, legal constraints prevent climate information from being fully utilized.Meeting the challenges posed by climate variations and climate change will require considerable revision of the policies and practices concerning how the region's natural resources are managed.An indication of the scope of such revisions comes from considering how government agencies have handled climate-related stresses in the past, like droughts and coastal erosion.In many cases, agencies cannot even make use of a good seasonal forecast in making short-term planning decision: the operating assumption is often that climate is constant and extremes do not occur.There are wide variations among the four sectors considered here in how management presently makes use of climate information.