The contribution of snowmelt to the rivers of the South Island, New Zealand

摘要

A new assessment of the mean annual (1981-2000) stream flow derived from snow and ice melt (Q_m) as a proportion of mean annual stream flows (Q_m/Q) for the South Island of New Zealand has been prepared. The assessment allows identification of the meltwater contribution of flows for any reach in the country, including bridge, irrigation take and lake locations. The snow melt estimates were generated by separating gridded daily precipitation into rainfall and snowfall components to provide mean annual snowfall and rainfall data. The ratio of the catchment-based accumulation of these precipitation components was then found, which is shown to be equivalent to the ratio of melt-derived flow to total flow. The assessment allows comparisons between sites, which were previously complicated by a paucity of assessments and differing methods. Based on the assessment, 3% of the South Island's mean annual stream flow is made up of meltwater. This is considerably less than estimates for regions of California, Austria, India and Chile. This difference is probably a reflection of the relative lack of seasonality in precipitation and the generally mild winter temperatures in the South Island. This low snow and ice melt contribution is problematic for irrigation schemes, in that artificial storage management is required if winter precipitation is to be retained for summer plant growth, but beneficial for hydro-electricity generation in that stream flows continue throughout the year, including winter (albeit often reduced) when energy demands are often high. The melt percentage data is available as an Excel? spreadsheet via http://dc.niwa.co.nz/niwa_dc/srv/en/metadata.show?uuid=02f3e247-2f78-562a-8712-675b4f3a0166.