Relationships between landscape, snowcover depletion, and regional weather and climate

The e€ects of landscape changes on winter and spring snow-related processes, and on regional weather and climate are not thoroughly understood. In this study, a climate version of the Regional Atmospheric Modelling System (ClimRAMS) is used to investigate the e€ects of landscape change on seasonal snow depletion and its corresponding e€ects on atmospheric and hydrologic processes. Two simulations of the 1996 spring melt season in the Rocky Mountains and Northern Great Plains are compared. The ®rst simulation utilizes the present-day vegetation distribution, and the second uses the same vegetation distribution with the exception that all forested regions are replaced by grassland. This vegetation modi®cation a€ects 18% of the domain and changes the leaf area index, transmissivity of the vegetation canopy to incoming solar radiation, roughness length, and surface albedo. Additional snow-related di€erences occur because the snow lying over grass, and the snow under the forest canopy, exist in dramatically di€erent radiative and thermal regimes. The snowcover changes resulting from the simulated deforestation in ̄uence the surface radiation balance, which leads to changes in surface sensible and latent energy ̄uxes, evaporation and transpiration rates, melt rates, and air temperature. The vegetation change also modi®es snowcover depletion rates, which in turn cause variations in runo€ production. Unmodi®ed regions are a€ected through hydrologic transport processes. The manifestations of these changes with respect to regional weather and climate are discussed. Copyright # 1999 John Wiley & Sons, Ltd.