The Changing Face of Arctic Snow Cover A Synthesi

Authors: Terry V Callaghan Margareta Johansson Ross D Brown Pavel Ya Groisman Niklas Labba Vladimir Radionov Roger G Barry Olga N Bulygina Richard L H Essery D M Frolov Vladimir N Golubev Thomas C Grenfell Marina N Petrushina Vyacheslav N Razuvaev David A Robinson Peter Romanov Drew Shindell Andrey B Shmakin Sergey A Sokratov Stephen Warren Daquing Yang

Publish Date: 2012/01/22

Volume: 40, Issue: 1, Pages: 17-31

PDF Link

Abstract

Analysis of in situ and satellite data shows evidence of different regional snow cover responses to the widespread warming and increasing winter precipitation that has characterized the Arctic climate for the past 40–50 years The largest and most rapid decreases in snow water equivalent SWE and snow cover duration SCD are observed over maritime regions of the Arctic with the highest precipitation amounts There is also evidence of marked differences in the response of snow cover between the North American and Eurasian sectors of the Arctic with the North American sector exhibiting decreases in snow cover and snow depth over the entire period of available in situ observations from around 1950 while widespread decreases in snow cover are not apparent over Eurasia until after around 1980 However snow depths are increasing in many regions of Eurasia Warming and more frequent winter thaws are contributing to changes in snow pack structure with important implications for land use and provision of ecosystem services Projected changes in snow cover from Global Climate Models for the 2050 period indicate increases in maximum SWE of up to 15 over much of the Arctic with the largest increases 15–30 over the Siberian sector In contrast SCD is projected to decrease by about 10–20 over much of the Arctic with the smallest decreases over Siberia 10 and the largest decreases over Alaska and northern Scandinavia 30–40 by 2050 These projected changes will have farreaching consequences for the climate system human activities hydrology and ecologyFrozen precipitation accumulating on a surface creates a snow cover Snow is an important and dominant feature of Arctic terrestrial landscapes with cover present for 8–10 months of the year Its extent dynamics and properties eg depth density water equivalent grain size and changes in structure throughout its vertical profile affect climate eg ground thermal regime human activities eg transportation resource extraction water supply use of land and ecosystem services as well as infrastructure hydrological processes permafrost extreme events including hazards such as avalanches and floods biodiversity and ecosystem processes Snow is therefore a significant component in the socioeconomics of Arctic societies The important physical properties that exert an influence on climate or moderate its effects Cohen and Rind 1991 include high shortwave albedo high thermal emissivity low heat conductivity large latent heat of fusion and low surface roughness while it stores and rapidly releases water in the melt season The combination of high albedo and low thermal conductivity promotes low surface temperatures and lowlevel temperature inversions The low thermal conductivity of snow allows it to insulate the surface from large energy losses in winter and this has major implications for the development of seasonally frozen ground and permafrostThe characteristics of Arctic snow cover are the result of a complex interplay of atmospheric and surface processes that determine not only the quantity of water stored as snow but also snowpack condition eg grain size density and ice layers The amount of snow accumulating on a surface is influenced by precipitation amount type and timing blowing snow transport and sublimation and vegetation interception However the character and evolution of highlatitude snowpack has the additional complexity of being particularly strongly dependent on blowing snow processes with the distribution and physical properties of snow on the ground closely linked to localscale variability in terrain and vegetation King et al 2008 The key largescale physiographic and climatic factors influencing the regional distribution of Arctic snow cover see Online supplementary material Fig A are elevation amount of vegetation cover spatial distribution of freezing temperatures and location of the main cyclone tracks bringing moisture into the Arctic Air temperature and elevation exert the strongest influences on the distribution of snow cover duration SCD across the Arctic Fig Ae with both continents exhibiting marked eastwest increases in snow cover in response to the modification of winter air masses over the cold dry continental interiors Land areas in the zone of −20°C mean winter temperatures see darker blue area in Fig Ac experience snow cover for most of the year The spatial distribution of snow water equivalent SWE the depth of liquid water that would result from melting the snow is more complex than SCD but is basically driven by moisture availability over the snow season reflected in the cyclone frequency map Fig Ad The highest snow accumulations in the Arctic are located in the coastal mountain regions and considerably more moisture penetrates into the western sector of the Eurasian Arctic than North America where the coastal mountains block moisture entering from the Pacific Ocean Regions with winter temperatures closer to freezing such as Scandinavia and the Pacific coasts of Russia and Alaska are also more likely to experience thaw and rainonsnow events that create ice layers in the snowpackThe high winds low temperatures and low snowfall amounts over the exposed tundra regions of the Arctic produce a snow cover that is typically quite shallow about 30–40 cm except in drifts and gullies with a windhardened surface layer “wind slab” overlying a less dense depth hoar “sugar snow” layer Derksen et al 2010 The average snow density remains close to 300 kg m−3 over much of the snow season but snow depth and properties can exhibit strong local variation with many exposed areas drifts dunes and zastrugi sharp irregular ridges on the snow surface formed by wind erosion and deposition In forested regions of the Arctic taiga and boreal forest snow cover is more uniform and less dense ~200 kg m−3 as the trees act as windbreaks and shade the snow from incoming solar radiation in the spring McKay and Gray 1981 In contrast north of the tree line where wind action compacts the snow snow density is higherBecause the Arctic’s snow cover is strongly related to temperature and moisture as described above past Walsh et al 2011a b this issue and projected changes in the Arctic’s temperature and precipitation are likely to result in changes in the characteristics of the Arctic’s snow cover with farreaching impacts on the climate system Callaghan et al 2011a b this issue human activities as well as infrastructure hydrological processes permafrost extreme events including hazards such as avalanches and floods biodiversity and ecosystem processes AMAP 2011 Callaghan et al 2011b this issue This article assesses current and projected changes in the Arctic’s snow cover It is part of a larger assessment of the Arctic’s entire cryosphere AMAP 2011 Callaghan et al 2011b this issueThere is a wide range of regularly observed snow cover information in the Arctic from in situ and satellite observations The SCD on the ground is one of the bestobserved variables in terms of resolution and longevity Snow depth and SWE are more difficult to monitor due to their high spatial variability large gaps in the in situ observing networks and difficulties in monitoring from satellites The indigenous peoples of the Arctic have a profound knowledge of changing snow conditions of practical importance for survival which has been passed from generation to generation and the Sáme observe snow stratigraphy that is important for reindeer access to vegetation Riseth et al 2010Long term meteorological stations in the Arctic red dots and mean monthly location of North Pole drifting stations blue dots in different sectors of the Arctic 1—Atlantic 2—NorthEuropean 3—WestSiberian 4—EastSiberian 5—Chukchi 6—Alaskan 7—Canadian

Keywords: