Causes of recent changes in western North American snowpack

Climate Dynamics (Impact Factor: 4.23). 01/2011; 38(9):1885-1899. DOI:10.1007/s00382-011-1089-y

ABSTRACT Monthly snow water equivalent (SWE) station observations and gridded temperature data are used to identify mechanisms by which
warming affects the temporal and geographical structure of changes in western North American mountain snowpack. We first exploit
interannual variability to demonstrate the sensitivity of snowpack to temperature during the various phases of the snow season.
We show that mechanisms whereby temperature affects snowpack emerge in the mid to late portion of the snow season (March through
May), but are nearly absent during the earliest phase (February), when temperatures are generally well below freezing. The
mid to late snow season is precisely when significant loss of snowpack is seen at nearly all locations over the past few decades,
both through decreases in snow accumulation and increases in snowmelt. At locations where April 1st SWE has been increasing
over the past few decades, the increase is entirely due to a significant enhancement of accumulation during the earliest phase
of the snow season, when the sensitivity analysis indicates that temperature is not expected to affect snowpack. Later in
the snow season, these stations exhibit significant snowpack loss comparable to the other stations. Based on this analysis,
it is difficult to escape the conclusion that recent snowpack changes in western North America are caused by regional-scale
warming. Given predictions of future warming, a further reduction in late season snowpack and advancement in the onset of
snowmelt should be expected in the coming decades throughout the region.

KeywordsSnow water equivalent–Climate change–Climate sensitivity–Trends–Surface observations

0 0
1 Bookmark
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: Recent observations have documented declining snow water equivalent (SWE) and earlier melt in the coastal Cascade and Sierra Nevada mountain ranges, and climate models suggest that warming temperatures will decrease snowpack storage in the higher-elevation mountain ranges of interior western North America. To date, however, observations of changing SWE or snowmelt have been limited to the state of Colorado in the intermountain west (IMW), defined here as the Rio Grande, Colorado River, and Great Basins, which supply water to the driest regions of North America. We used daily SNOTEL data collected between 1984 and 2009 combined with the nonparametric regional Kendall test to demonstrate significant and widespread changes in the duration of snow cover in these river basins. Daily SNOTEL data demonstrated that basin average maximum SWE occurred as early as 7 March (Lower Colorado River Basin) and as late as 13 April (Upper Colorado, Yampa, and White River Basins). Although significant increases in winter temperature (T) were widespread, there were minimal changes in the day of maximum accumulation and no indications from SWE to winter precipitation ratios (SWE:P) and winter T observations that a transition from snow to rain had occurred. While there was little change in day of maximum accumulation, the duration of snow cover decreased in 11 of 13 drainage regions, and snowmelt center of mass (SM50) advanced 1 to 4 days per decade in 6 of 13 regions. There were significant trends toward a faster SM50 and shorter duration of snow cover in the highest-elevation regions (>2800 m) of the Colorado River Basin, suggesting that winter T and P may not be the primary driver of change. Our results show that the IMW hydroclimate is both spatially and temporally variable, with few changes in winter T and P in the Great Basin and drier and warmer winters in the Colorado River and Rio Grande Basins. The changes in snowmelt timing also were variable, with a shorter SM50 and less maximum SWE in the Colorado River and Rio Grande Basins. The variable response of snowpacks in the IMW to widespread warming highlights the need for additional research into the mass and energy balance of these continental snowpacks.
    Water Resources Research 11/2012; 48(11):11501-. · 3.15 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: Given its large population, vigorous and water-intensive agricultural industry, and important ecological resources, the western United States presents a valuable case study for examining potential near-term changes in regional hydroclimate. Using a high-resolution ensemble climate model experiment, we find that increases in global radiative forcing result in an acceleration of decreases in spring snowpack and a transition to a substantially more rain-dominated water resources regime over the next three decades. These hydroclimatic changes are associated with increase in cold-season days above freezing and decreases in cold-season snow-to-precipitation ratio. The changes in the temperature and precipitation regime in turn result in shifts toward earlier central snowmelt, baseflow and runoff dates throughout the region, as well as reduced annual and warm-season snowmelt and runoff. The simulated hydrologic response is dominated by changes in temperature, increasing confidence in the model projections. Given the impacts of recent trends in snowpack and snowmelt runoff, the projected acceleration of hydroclimatic change in the western U.S. has important implications for the availability of water for agriculture, hydropower and human consumption, as well as for the risk of wildfire, forest die-off, and loss of riparian habitat.
    AGU Fall Meeting Abstracts. 12/2011;


1 Download
Available from