Topographic control of snowpack distribution in a small catchment in the central Spanish Pyrenees: intra- and inter-annual persistence

In this study we analyzed the relations between terrain characteristics and snow depth distribution in a small alpine catchment located in the central Spanish Pyrenees. Twelve field campaigns were conducted during 2012 and 2013, which were years characterized by very different cli- matic conditions. Snow depth was measured using a long range terrestrial laser scanner and analyses were performed at a spatial resolution of 5 m. Pearson's r correlation, mul- tiple linear regressions (MLRs) and binary regression trees (BRTs) were used to analyze the influence of topography on the snow depth distribution. The analyses were used to iden- tify the topographic variables that best explain the snow dis- tribution in this catchment, and to assess whether their contri- butions were variable over intra- and interannual timescales. The topographic position index (index that compares the rel- ative elevation of each cell in a digital elevation model to the mean elevation of a specified neighborhood around that cell with a specific shape and searching distance), which has rarely been used in these types of studies, most accurately explained the distribution of snow. The good capability of the topographic position index (TPI) to predict snow dis- tribution has been observed in both, MLRs and BRTs for all analyzed days. Other variables affecting the snow depth distribution included the maximum upwind slope, elevation and northing. The models developed to predict snow dis- tribution in the basin for each of the 12 survey days were similar in terms of the explanatory variables. However, the variance explained by the overall model and by each topo- graphic variable, especially those making a lesser contribu- tion, differed markedly between a year in which snow was abundant (2013) and a year when snow was scarce (2012), and also differed between surveys in which snow accumula- tion or melting conditions dominated in the preceding days. The total variance explained by the models clearly decreased for those days on which the snowpack was thinner and more patchily. Despite the differences in climatic conditions in the 2012 and 2013 snow seasons, similarities in snow distribu- tions patterns were observed which are directly related to ter- rain topographic characteristics.

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