Understanding the Elevation-Dependence of Climate Warming over Complex Terrain in High-Resolution Simulations of Regional Climate Change

Numerous observational and modeling studies have suggested that over mountainous terrain certain elevations experience enhanced rates of climate warming relative to the surrounding region. In many of these studies high-elevation locations were found to experience the fastest warming rates. A variety of physical mechanisms have been proposed but there is no consensus as to the dominant cause.

We examine elevation-dependent warming in a pair of regional climate model (RCM) simulations with very high horizontal resolution (4-km grid). The domains of the two simulations cover the Rocky Mountains and the continental United States as a whole. Climate change simulations are conducted using the “pseudo global warming” framework to focus on the regional response to large-scale thermodynamic and radiative climate changes.

In both simulations the snow-albedo feedback plays a dominant role in determining the elevation-dependence of climate warming, with enhanced warming at elevations where changes in snow cover and albedo are maximized. The elevation of maximum warming varies seasonally, following the margin of the snowpack. Additional simulations where the snow-albedo feedback is artificially suppressed are used to show that other mechanisms (such as elevation-dependent free-tropospheric warming, water vapor feedbacks, or cloud feedbacks) do not play an appreciable role in contributing to elevation-dependent warming over the Rocky Mountains. Variations in the snow albedo feedback and elevation-dependent warming between different mountain ranges are also investigated.