International Snow Science Workshop Proceedings - Montana State University Library

Item: Modelling the Spatial Moments of SWE, Taking into Account Changes in Snow Free Areas

• • Title: Modelling the Spatial Moments of SWE, Taking into Account Changes in Snow Free Areas

    Proceedings: 2010 International Snow Science Workshop

    Authors:

    • Thomas Skaugen  [ Norwegian Water Resources & Energy Directorate (NVE), Oslo, Norway ]
    • Frode Randen  [ Norwegian Water Resources & Energy Directorate (NVE), Oslo, Norway ]

    Date: 2010

    Abstract: In a previous paper, a method for estimating the spatial frequency distribution of snow water equivalent (SWE) was put forward. The accumulate snow reservoir, was modelled as a sum of correlated (in time) gamma distributed variables. This methodology was constrained to estimate the moments of spatial SWE for snow covered areas and the resulting spatial frequency distribution is described as “conditional”, i.e. conditional on snow. In order to implement the method in hydrological models, we have to take into account the change of snow coverage and thus provide the unconditional moments of the spatial distribution. The spatial variance of SWE for both an accumulation- and a melting event is evaluated through the covariance matrix. For accumulation events, we have only positive elements, whereas for melting events, we have both positive and negative contributions. The negative contributions become dominant only after a period into the melting season. At the onset of the melting season, the spatial variance thus continues to increase for later on to decrease. This behaviour is consistent with observations and by some authors dubbed the “hysteretic” effect. The conditional and unconditional moments are estimated by the following procedure. The input values (rainfall and potential melting) are unconditional, but are made conditional by adjusting for changes in snow coverage. Then conditional moments are estimated. The unconditional moments are then estimated using the conditional moments and the snow coverage. The modelled conditional and unconditional moments are in close agreement with the observed.

    Object ID: ISSW_P-025.pdf

    Language of Article: English

    Presenter(s): Unknown

    Keywords: swe, gamma distributed variables, hysteretic effect, spatial distribution

    Page Number(s): Unavailable

    Subjects: snow water equivalent snow coverage

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