Seven Years of Snow Cover Monitoringwith Modis to Assess and Improve Modelling of Catchments Discharge in New Zealand

Situated in the Southern Alps, the Waitaki basin is the most important hydro catchment in New Zealand and provides approximately one-third of New Zealand’s hydro electricity production. Three sub-catchments receive most of the precipitation: Ohau, Pukaki, and Tekapo. In this alpine region an important fraction of the total precipitation falls as snow, which accumulates during winter months from April to October. Thus, a large part of the water resource is temporarily stored as seasonal snow cover and the snowmelt from these catchments is estimated to contribute from 18% to 24% of the total annual runoff and up to 40% to 50% of the spring and summer inflows [1]. It has been long-established that satellite remote sensing is a very powerful tool to monitor snow cover in remote and hardly accessible areas. Considerable efforts have been made recently to routinely produce maps of sub-pixel snow fraction of the area from NASA’s MODderate Resolution Imaging Spectroradiometer (MODIS) [2]. A temporal time series of MODIS-derived snow maps is used to assess the performance of the existing snow pack modelling strategy (SnowSim-Pukaki). Furthermore, daily meteorological data (i.e., temperature and precipitations) and the frequent observations of the snowpack from MODIS enable the use of the Snowmelt Runoff Model (SRM) [3, chap. 11] to simulate the discharge of the three sub-catchments over the hydrological years 2000–2007.