Northern Hemisphere spring snow cover variability and change over 1922–2010 including an assessment of uncertainty
1Climate Processes Section, Climate Research Division, Environment Canada @ Ouranos, 550 Sherbrooke St. West, 19th Floor, Montréal, QC, H3A 1B9, Canada
2Department of Geography, Rutgers University, 54 Joyce Kilmer Avenue Piscataway, NJ 08854-8054, USA
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 estimates from regression analysis and intercomparison of multiple datasets. The uncertainty analysis indicated 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 showed there are larger uncertainties monitoring spring SCE over Eurasia (EUR) than North America (NA) due to the more complex regional character of the snow cover variability with the largest dataset uncertainty located over eastern Eurasia in a large region extending from the Tibetan Plateau across northern China.
Trend analysis of the updated SCE series provided evidence that NH spring snow cover extent has undergone significant reductions over the past ~90 years and that the rate of decrease has accelerated over the past 40 years. The rate of decrease in March and April NH SCE over the 1970–2010 period is ~7–8 million km2 per 100 years which corresponds to an 8–11% 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 consistent with recent warming trends over northern mid-latitude land areas with NH SCE exhibiting significant negative correlations to air temperature anomalies in March and April. The NH spring SCE-temperature sensitivity has remained relatively stable over the period of record although there is some evidence of contrasting changes in temperature sensitivity over both continents in April. There is 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.