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Assessing the hydrological impacts of climate change in the Pacific Northwest (PNW) region of the United States is important. Many global circulation models (GCMs) have a wide range of temperature and precipitation predictions for the PNW region (Bureau of Reclamation, 2011). Numerous studies have reported that decreasing snow pack, increasing temperatures and decreasing streamflow for many basins. For instance, Mote (2003) indicates that annual average temperatures in the Northwest rose faster than the global average during the 20th century. This warming occurred mostly during the winter and spring. The predominance of winter and spring warming, especially in regard to extreme minimum temperatures, was confirmed more recently in a smaller study at two locations: one in Western Montana and the other in British Columbia (Caprio et al., 2009). The warming climate has resulted in a lengthened growing season (Kunkel et al., 2004), decline of snowpack (Mote, 2006), and earlier timing of the spring runoff (Stewart et al., 2005; Hamlet and Lettenmaier, 1999). Water supply in the West is vulnerable to climatic change, mainly because it relies heavily upon the capture of the spring runoff. Precipitation typically accumulates in the mountains as snowpack and is released during the spring melt, which may continue at high elevations into July. Warmer temperatures are likely to lead to more rain and less snow in the winter, causing an increase in the wintertime streamflow and decrease in spring runoff. Warmer weather is also likely to cause snowpack to retreat to higher elevations and experience earlier melt (Hamlet and Lettenmaier, 1999).


Published in Climate Change / Book 1 (ISBN 978-953-307-419-1).

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