Surface albedo in Ny-A ˚ lesund, Svalbard: variability and trends during 1981–1997 Jan-Gunnar Winther a, * , Fred Godtliebsen b , Sebastian Gerland a , Pa ˚l Erik Isachsen a a Norwegian Polar Institute, Polar Environmental Centre, N-9296 Tromsø, Norway b Department of Mathematics and Statistics, University of Tromsø, N-9037 Tromsø, Norway Received 3 February 2000; accepted 1 December 2000 Abstract Since 1981, hourly values of albedo have been measured routinely at Norwegian Polar Institute’s research station in Ny- A ˚ lesund, Svalbard. We have undertaken statistical analysis of the time series 1981–1997 to investigate potential long-term variability and trends in the albedo data set. The following questions have been raised and answered by regression analysis: (i) Has the time of beginning of snow melt changed? (ii) Have melt rates changed? (iii) Has the time of snow arrival in fall changed? (iv) Has the period without snow cover changed? The period without snow on the ground is studied because of its importance for tundra characteristics as a habitat for biota, e.g. length of the growth season. Our data show that albedo varies seasonally, with large variations in spring and autumn and much smaller variations in winter and summer. The variability is reasonably constant within each season. Density estimates of the albedo data suggest that the dates with highest likelihood for (i) start of snow melt and (ii) start of snow formation are 5th of June and 17th of September, respectively. Highest probability for the length of snow-free season is 94 days. None of the tests indicated any significant trends (or indications of climate change) in the 17-year record of albedo, that means that the four questions above were all answered by ‘‘no.’’ Correlation with the North Atlantic Oscillation (NAO) index is also investigated. No correlation between the NAO index and albedo nor temperature or precipitation was found. Even so, because of the short duration that our data set spans, we cannot rule out that such a correlation exists on decadal time scales. D 2002 Elsevier Science B.V. All rights reserved. Keywords: surface albedo; snow melt; climate change; North Atlantic Oscillation; Svalbard 1. Introduction Dry, weakly metamorphosed snow reflects most of the incoming short-wave radiation back to space (Winther, 1993a; Wiscombe and Warren, 1980). Then, during snow melt, the integrated short-wave albedo decreases rapidly and may drop from about 80% to about 10% within a few weeks, completely changing the surface energy-balance (Ko ¨nig and Sturm, 1998). Further, snow melt provides the bulk of the yearly runoff and plays an important role in the hydrological regime, e.g. for processes such as erosion, sediment transport, and infiltration in the active layer. In addi- tion, the presence of snow also governs the time when vegetation can grow, and therefore, the quality of habitats available for plants, birds, and animals (Ger- land et al., 1999). Thus, knowledge on surface albedo 0921-8181/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0921-8181(01)00103-5 * Corresponding author. Tel.: +47-77-75-05-00; fax: +47-77- 75-05-01. E-mail address: winther@npolar.no (J.-G. Winther). www.elsevier.com/locate/gloplacha Global and Planetary Change 32 (2002) 127 – 139