SCALE EFFECTS IN A DISTRIBUTED SNOW WATER EQUIVALENCE AND SNOWMELT MODEL FOR MOUNTAIN BASINS

We investigated the effect of increasing spatial and temporal resoluti ons on modelled distributions of snow water equivalence (SWE) and snow melt in the Emerald Lake Watershed (ELW) of the Sierra Nevada of Calif ornia, USA. We used a coupled remote sensing/distributed energy balanc e snowmelt model (SNODIS), and used previously validated results from a high spatial (30 m) and temporal (hourly) resolution model run in EL W as a control. We selected spatial resolutions that are commensurate with standard product DEMs (digital elevation models) or with existing or planned satellite remote sensing data, and temporal resolutions th at are factors of typical operational intervals for meteorological dat a, We degraded the spatial resolution of the DEM from 30 m to 90, 250 and 500 m prior to computing the distributed micrometeorological data. We degraded the classified remote sensing data to the same spatial re solutions prior to computing the duration of the snow cover. Similarly , we degraded the temporal resolution of the micrometeorological data from I h to 3 and 6 h prior to computing the distributed energy balanc e and snowmelt. We compared mean basin SWE, basin snowpack water volum e and the spatial patterns of SWE from each test with our previous, hi gh resolution results. We found no significant differences between the mean basin-wide SWE computed from the 250 m and 500 m spatial resolut ions and that of our high resolution control, regardless of temporal r esolution. At each temporal resolution mean basin SWE was overestimate d at the 90 m resolution by 14-17%, Coarsening of the spatial resoluti on did result in a loss of explicit information regarding the location of SWE in the basin, as expected. We discuss these results in terms o f their implications for applying the SNODIS model to larger regions. (C) 1998 John Wiley & Sons, Ltd.