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snow

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    The snow melt estimates were generated through the separation of daily precipitation into rainfall and snowfall components to provide 1981-2010 mean annual snowfall and rainfall maps. The ratio of the catchment-based accumulation of these precipitation components was then found for each river reach in the New Zealand River Environment Classification (REC), which is equivalent to the ratio of snow and ice melt to flow. The REC user guide is available at: http://www.mfe.govt.nz/environmental-reporting/about/tools-guidelines/classifications/freshwater/rec-user-guide-2010.pdf Kerr, T. 2013: The contribution of snowmelt to the rivers of the South Island, New Zealand. Journal of Hydrology (NZ) Accepted.

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    This Report assembles an eleven year time series for the period 2001 to 2011 of snow cover area in New Zealand. A dataset is prepared based on the MODIS/Terra Snow Cover 8-Day L3 Global 500m Grid, Version 5 data (MOD10A2.5, available from the National Snow and Ice Data Center NSIDC, Boulder, Colorado USA). The MOD10A2.5 dataset indicates the maximum snow cover extent over an eight-day compositing period. It provides a seamless coverage of snow presence at regularly spaced time intervals, while minimizing the obscuration by clouds. Each year is composed of 46 epochs, each of 8 consecutive days starting on the first day of the year and extending in to the next year. An algorithm based on a trajectory analysis of land cover through time is used to infer the status of remaining pixels obscured by cloud in the composite period. This leads to a time series of virtually cloud-free composite snow cover maps that are readily imported into GIS packages for analysis of spatial and temporal variability.