Measurements of the surface fluxes of radiation, heat and water vapour were made at three tundra sites near Ny-Ålesund, Svalbard for the active seasons (June to September) of 1995 and 1996. In 1995 the snow melted completely in early June, in 1996 the deeper snow pack resulted in the persistence of snow until July. Thus the snow free period was 50% longer in 1995 resulting in larger cumulative evaporation and energy inputs. In this region the snow melt is dominated by radiation input, a result of the low air temperatures and possible control of the air temperature by the surrounding sea, snow and ice fields. During the snow-free period the evaporative ratio [LE/(LE+H)] varied with surface type. At two sites, where there was a continuous cover of soil, the evaporative ratio was consistently equal to 0.5, except for a few days after rainfall when it rose to unity. This latter rise was probably due to the increased evaporation from the soil, mosses and lichens after wetting by rainfall. At a third site, with a predominantly stony surface, the evaporative ratio was lower (between 0.2 and 0.3), again rising during and after rainfall. The measurements from 1995 show the summer evaporation was 160% of the summer rainfall. However there was no evidence of a reduction of evaporation during extended dry periods. In 1996 the radiation inputs and evaporation were much reduced by the shorter active season and rainfall exceeded evaporation. The timing of the snow and snowmelt and thermal condition of the surface layers is thus important to the hydrology, the surface energy balance and the carbon balance of this region.

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