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Keywords:

  • climate change;
  • snow hydrology;
  • modelling

Abstract

For most of the global land area poleward of about 40° latitude, snow plays an important role in the water cycle. The (seasonal) timing of runoff in these areas is especially sensitive to projected losses of snowpack associated with warming trends, whereas projected (annual) runoff volume changes are primarily associated with precipitation changes, and to a lesser extent, with changes in evapotranspiration (ET). Regional studies in the USA (and especially the western USA) suggest that hydrologic adjustments to a warming climate have been ongoing since the mid-twentieth century. We extend the insights extracted from the western USA to the global scale using a physically based hydrologic model to assess the effects of systematic changes in precipitation and temperature on snow-affected portions of the global land area as projected by a suite of global climate models. While annual (and in some cases seasonal) changes in precipitation are a key driver of projected changes in annual runoff, we find, as in the western USA, that projected warming produces strong decreases in winter snow accumulation and spring snowmelt over much of the affected area regardless of precipitation change. Decreased snowpack produces decreases in warm-season runoff in many mid- to high-latitude areas where precipitation changes are either moderately positive or negative in the future projections. Exceptions, however, occur in some high-latitude areas, particular in Eurasia, where changes in projected precipitation are large enough to result in increased, rather than decreased, snow accumulation. Overall, projected changes in snowpack and the timing of snowmelt-derived runoff are largest near the boundaries of the areas that currently experience substantial snowfall, and at least qualitatively, they mirror the character of observed changes in the western USA. Copyright © 2008 John Wiley & Sons, Ltd.