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Guo-Yue Niu and Zong-Liang Yang

the climate system by altering soil thermal and hydrological properties. Freezing of soil water delays the winter cooling of the land surface, and thawing of the frozen soil delays the summer warming of the land surface ( Poutou et al. 2004 ). Frozen soil also affects the snowmelt runoff and soil hydrology by reducing the soil permeability. Runoff from the Arctic river systems is about 50% of the net flux of freshwater to the Arctic Ocean ( Barry and Serreze 2000 ). This is a large percentage when

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David W. Clow

. Observed changes include decreases in the proportion of precipitation falling as snow ( Knowles et al. 2006 ), decreases in 1 April snow-water equivalent (SWE) in snowpacks ( Mote 2006 ), and earlier runoff during the spring snowmelt period ( Cayan et al. 2001 ; McCabe and Clark 2005 ; Regonda et al. 2005 ; Stewart et al. 2005 ). These studies indicated that in the west, changes were most pronounced in the Cascade Mountains, the northern Sierra Nevada, and the northern Rocky Mountains, where

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Jessica D. Lundquist and Alan L. Flint

1. Introduction In the western United States, over half of the water supply comes from mountain snowpacks, and over the past 50 yr, warmer winters and springs have led to earlier snowmelt ( Stewart et al. 2005 ). The fraction of annual streamflow that runs off during late spring and early summer has declined by 10% to 25% ( Roos 1991 ; Wahl 1992 ; Dettinger and Cayan 1995 ). Snowmelt runoff timing has advanced by approximately one to three weeks in the large majority of mountainous catchments

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Sebastian H. Mernild and Glen E. Liston

land surfaces are typically visibly homogeneous with a covering of ice and snow, and snow, respectively: high albedo and low amounts of absorbed solar radiation therefore provide small differences in energy partitioning between the marine and terrestrial surfaces ( Hansen et al. 2008 ). After terrestrial snowmelt in the spring, the land surface warms up, giving rise to a temperature gradient between the land and the still frozen sea. During daytime, cold and moist sea breezes affect the air

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Pablo F. Dornes, John W. Pomeroy, Alain Pietroniro, and Diana L. Verseghy

during the snow season due to internal feedback processes. Similarly, the Snow Model Intercomparison Project (SnowMIP) found a wide range of capabilities in simulating snow water equivalent (SWE) at a point during the accumulation and melt periods between the models ( Etchevers et al. 2004 ). Small-scale heterogeneity is especially important in arctic and subarctic mountain environments during the spring snowmelt season. Over the winter, snow is blown from areas of high wind exposure to sheltered

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Holger Fritze, Iris T. Stewart, and Edzer Pebesma

comparatively narrow window of time during which runoff is generated for the year. In rain-dominated and mixed runoff regimes, the largest fraction of runoff comes during winter and early spring, closely following the precipitation pattern. For snowmelt-dominated basins, most of the winter precipitation is stored as snow in the higher elevations of the watershed and is released during spring and early summer. This spring snowmelt runoff pulse contributes up to 75% of total annual runoff for the snowmelt

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Jinwon Kim, Yu Gu, and K. N. Liou

static stability and vertical motions. Gueymard et al. (2000) also reported that dust originating from China has affected the surface insolation in the United States, and may have altered the regional circulation and water cycle. In a regional model study over East Asia, Giorgi et al. (2002) reported that anthropogenic sulfates can induce a negative radiative forcing at the top of the atmosphere (TOA) by as much as −15 W m −2 . The aerosol radiative forcing on spring snowmelt in the Sierra Nevada

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Boksoon Myoung, Seung Hee Kim, Jinwon Kim, and Menas C. Kafatos

1. Introduction Winter snowpack is one of the most important components of water storage and supply in the western United States (WUS) ( Serreze et al. 1999 ; Mote et al. 2005 ). Therefore, a pronounced trend or variability of the snowpack amount (e.g., decreasing trends in winter snowpack) and snowmelt is of great concern, especially in the upper southwestern United States (UP_SW), which includes California, Nevada, Utah, and Colorado. A number of previous studies have documented decreasing

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John Pomeroy, Chad Ellis, Aled Rowlands, Richard Essery, Janet Hardy, Tim Link, Danny Marks, and Jean Emmanuel Sicart

variable in forested environments ( Link and Marks 1999 ; Hardy et al. 2004 ; Link et al. 2004 ). Therefore, it is the purpose of this paper to examine the variability of shortwave irradiance in coniferous forest environments during snowmelt to estimate the significance of this variability to snow-covered area depletion. A companion paper ( Essery et al. 2008 ) focuses on estimating the spatial distribution of shortwave transmission through coniferous canopies using remote sensing and explicit

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D. Marks, A. Winstral, G. Flerchinger, M. Reba, J. Pomeroy, T. Link, and K. Elder

evaluate fluxes simulated by a widely applied and validated energy balance snowmelt model. As a method, EC has been in wide use since the early 1990s, but only in the past decade or so have EC systems been applied over natural field sites with complex canopy and terrain structure. In the past few years, the reliability of EC systems has improved, and the size and power requirements have been reduced to the point that they can be operated unattended at a remote site without line power. Although the EB

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