Abstract:Multivariate statistical analysis was used to explore relationships between catchment topography and spatial variability in snow accumulation and melt processes in a small headwater catchment in the Spanish Pyrenees. Manual surveys of snow depth and density provided information on the spatial distribution of snow water equivalent (SWE) and its depletion over the course of the 1997 and 1998 melt seasons. A number of indices expressing the topographic control on snow processes were extracted from a detailed digital elevation model of the catchment. Bivariate screening was used to assess the relative importance of these topographic indices in controlling snow accumulation at the start of the melt season, average melt rates and the timing of snow disappearance. This suggested that topographic controls on the redistribution of snow by wind are the most important influence on snow distribution at the start of the melt season. Furthermore, it appeared that spatial patterns of snow disappearance were largely determined by the distribution of snow water equivalent (SWE) at the start of the melt season, rather than by spatial variability in melt rates during the melt season. Binary regression tree models relating snow depth and disappearance date to terrain indices were then constructed. These explained 70-80% of the variance in the observed data. As well as providing insights into the influence of topography on snow processes, it is suggested that the techniques presented herein could be used in the parameterization of distributed snowmelt models, or in the design of efficient stratified snow surveys.

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19The hydrological and geomorphic effects of land use/land cover changes, 20 particularly those associated with vegetation regrowth after farmland abandonment were 21 investigated in the Central Spanish Pyrenees. The main focus was to assess the 22 interactions among slope, catchment, basin, and fluvial channel processes over a range 23 of spatial scales. In recent centuries most Mediterranean mountain areas have been 24 subjected to significant human pressure through deforestation, cultivation of steep 25 slopes, fires, and overgrazing. Depopulation commencing at the beginning of the 20th 26 century, and particularly since the 1960s, has resulted in farmland abandonment and a 27 reduction in livestock numbers, and this has led to an expansion of shrubs and forests.

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