Northern Hemisphere spring snow cover variability and change over 1922–2010 including an assessment of uncertainty

Abstract

Abstract. An update is provided of Northern Hemisphere (NH) spring (March, April) snow cover extent (SCE) over the 1922–2010 period incorporating the new climate data record (CDR) version of the NOAA weekly SCE dataset, with annual 95% confidence intervals estimated from regression analysis and intercomparison of multiple datasets. The uncertainty analysis indicates a 95% confidence interval in NH spring SCE of ±5–10% over the pre-satellite period and ±3–5% over the satellite era. The multi-dataset analysis shows larger uncertainties monitoring spring SCE over Eurasia (EUR) than North America (NA) due to the more complex regional character of the snow cover variability and larger between-dataset variability over northern Europe and north-central Russia. Trend analysis of the updated SCE series provides evidence that NH spring snow cover extent has undergone significant reductions over the past ~90 yr and that the rate of decrease has accelerated over the past 40 yr. The rate of decrease in March and April NH SCE over the 1970–2010 period is ~0.8 million km2 per decade corresponding to a 7% and 11% decrease in NH March and April SCE respectively from pre-1970 values. In March, most of the change is being driven by Eurasia (NA trends are not significant) but both continents exhibit significant SCE reductions in April. The observed trends in SCE are being mainly driven by warmer air temperatures, with NH mid-latitude air temperatures explaining ~50% of the variance in NH spring snow cover over the 89-yr period analyzed. However, there is also evidence that changes in atmospheric circulation around 1980 involving the North Atlantic Oscillation and Scandinavian pattern have contributed to reductions in March SCE over Eurasia.

Temperature and Snow-Mediated Moisture Controls of Summer Photosynthetic Activity in Northern Terrestrial Ecosystems between 1982 and 2011

“…A positive association has also been observed between deeper snowpack and summer NDVI in central Siberia and parts of North America [34,35]. Thus, recent declines in winter snowpack and snow cover duration documented in several regions of northern Eurasia and North America [36][37][38] are likely to have affected ecosystem function.…”

“…Thus, this negative response of summer photosynthetic activity to earlier spring thaw is likely a reflection of soil moisture deficits resulting from both insufficient soil moisture recharge with shallow snowpacks and increased moisture depletion with an extended evaporative season. Taken together, these emerging results suggest that recent changes in snow regimes associated with rapid climatic warming [36][37][38] are likely to have played an important, albeit unrecognized, role in the observed spatiotemporal patterns of summer photosynthetic activity across a large portion of the boreal region, particularly in North America.…”

“…Ongoing trends toward thinner snowpacks and earlier snowmelt and growing seasons [9,36,38] may be further enhancing summer drying in some regions by extending the period of evapotranspiration into the spring and thus accelerating seasonal soil moisture depletion [10,35]. Indeed, pioneering modeling studies conducted in the 1980s using simple climate models suggested that, along with increasing evaporation demand, earlier snowmelt also contributed to projected summer drying at northern latitudes as a result of anthropogenic warming [75].…”

“…This is because the (monthly) resolution of the meteorological forcing data is quite coarse. However, the timing of snowmelt is closely associated with the amount of snow accumulated in the winter snowpack [33] and thus our scPDSI estimates may still incorporate the effect of the widespread reduction in spring snow cover observed at northern latitudes [36].…”

“…Recent studies based on satellite and in-situ observations have shown that rapid winter/spring warming and changes in interdecadal climate modes since around 1991 have led to a significant decline in snowpack accumulation and snow cover duration across most of Alaska and Canada despite increasing winter precipitation [36][37][38]94,95]. In some regions of the North American Cordillera, the recent loss of snowpack is unprecedented over the past millennium [96].…”