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Climate-related research activities at the Loch Vale WEBB site

Water resources

High-elevation and high-latitude watersheds in North America receive the majority of their annual precipitation as winter and spring snow [Serreze et al., 1999]. Most of this snow accumulates in seasonal snowpacks, which represent a natural storage reservoir whose size exceeds that of manmade reservoirs in many river basins of the world [Mote, 2006; Nijssen et al., 2001]. Arid regions, such as western United States, that receive relatively little precipitation during summer months are heavily dependent on natural and manmade storage to provide water for agriculture, industry, and drinking during the dry summer and fall seasons [Barnett et al., 2005].

Three of the five WEBB watersheds are in terrain with seasonal snowpacks. Loch Vale, in the Colorado Rocky Mountains, typically receives 70-80% of annual precipitation in the form of snow; investigation of hydroclimatic processes that influence the timing of snowmelt is an important area of research. Recently, WEBB researchers used a new statistical method, the Regional Kendall Test (RKT), to document changes in the timing of snowmelt and streamflow runoff in Loch Vale and elsewhere in Colorado [Clow, submitted 2008]. Snowmelt and streamflow are occurring approximately two weeks earlier now than in the late 1970s, and the changes were positively correlated with increasing springtime air temperatures, and negatively correlated with maximum snow water content of the snowpack [Clow, submitted 2008]. Use of the RKT allowed identificaton of trends that had previously gone undetected due to large interannual variability and the relatively short period of record of the SNOTEL data sets [Stewart et al., 2005].

Average annual nitrate deposition for the Rocky Mountains, 1992–1999.

Analyses of temporal and spatial variations in the depth and water content of seasonal snowpacks has been another area of extensive research at the Loch Vale WEBB site. Spatial variations in snowpack depth and water content have been monitored since 1991t through the WEBB program, permitting development of snowpack distribution models using a combination of binary decision tree and geostatistical techniques [Balk and Elder, 2000; Cline, 1995]. Using data from Loch Vale and 65 additional sites, the methods have been applied to the Rocky Mountain region, and solute chemistry has been added to the analysis to develop maps of nitrogen, sulfur, and acidity deposition in snow [Nanus et al., 2003]. Long-term, repeat sampling at these sites permitted an evaluation of temporal trends in solute deposition that accounted for climate variability [Ingersoll et al., 2008]. This allowed separation of trends attributable to climate versus those due to variations in nitrogen and sulfur emissions [Ingersoll et al., 2008].

Analysis of streamflow records for climate-induced trends in cold climates has been hampered by the poor quality of discharge records during winter months, which is due to the presence of in-channel ice that causes variable backwater conditions and alters the stage-discharge relationship. WEBB research contributed to the recent development of an automated dye-dilution gaging system, which can provide high-quality, real-time discharge data at 8 hour intervals in ice-affected streams [Clow and Fleming, 2008].

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