A fast, physically based point snowmelt model for use in distributed applications.pdf

A fast, physically based point snowmelt model for use in distributed applications Mary Albert* and Greg Krajeski Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03755, USA Abstract: A new mathematical solution to the problem of water ˉow through snow is presented and its implementation in a snowmelt model, SNAP, is discussed. An analytical solution for vertical water ˉow through homogeneous snow is developed and formulae that allow the solution to accommodate time-varying surface input from rain or snowmelt are derived. This facilitates use of the technique in a computer snowmelt model. Because the new technique requires no matrix computation, it is su?ciently computationally e?cient to be a candidate for use in watershed-scale, distributed forecasting systems. Because it is a physically based model that takes into account the e?ect of the snow itself on the timing and magnitude of outˉow, the model allows more accurate prediction of the magnitude and timing of snowmelt than in currently employed operational models. Results of the new model agree well with previous theoretical solutions and with ?eld measurements of melt and rain-on-snow events in a seasonal snow pack. # 1998 John Wiley Sons, Ltd. KEY WORDS snowmelt model; distributed applications; physically based model INTRODUCTION Because snowmelt runo? is a major component of the hydrological cycle and is also a major cause of spring- time ˉooding and severe erosion, there is a need for accurate, e?cient snowmelt models for forecasting appli- cations. Modern hydrological forecasting techniques often employ distributed modelling systems [e.g. using geographic information systems (GIS)]. Distributed modelling applications apply point (one-dimensional) process models at many locations over wide and varied terrain, enabling the user to incorporate the e?ects of di?ering slope, aspect, elevation and ground cover in watershed forecasting procedures, for example. The increasingly widespread