| For mountainous regions, and regions downstream, the climatology of mid-latitude orographic precipitation determines the susceptibility to hazards such as flooding and landslides while also cotrolling the volume and timing of streamflow and fresh water resources. However, due to modeling and observational challenges, many aspects of the climatology of mountain precipitation remain poorly understood. This thesis uses a synthesis of numerical models, theory, and field observations, loosely focused on the Cascade and Olympic Mountains of western North America, to investigate in detail a number of general aspects of mid-attitude orographic precipitation.;First, the climatology of ridge-valley scale precipitation patterns is investigated by analysis of several years of data from the Olympic Mountains, both from archived operational mesoscale numerical model forecasts and a special dense observing network of precipitation gauges. By simulating and analyzing case studies, the physical processes responsible for the mean pattern and variations in the pattern are diagnosed. Large (> 50%) enhancement of precipitation over ridges relative to valleys a few kilometers away is found to be a very robust feature of the region's climate, and the climatological patterns are surprisingly well-simulated by a mesoscale model (despite frequent errors for individual storms).;The impact of large climatological gradients in mountain precipitation, such as those found in the Olympic mountains, on patterns of landslide susceptibility is also investigated. This is accomplished using an idealized model of shallow landslides, forced by the climatology developed from mesoscale model forecasts. Results suggest that small-scale maxima in climatological precipitation may play an important role in making certain regions more susceptible to slope failure. Furthermore, the use of unadjusted lowland precipitation data to characterize conditions on nearby mountain slopes may lead to a substantial underestimate of landslide hazard.;Next, the controls on the sensitivity of mountain snowpack accumulation to climate warming are investigated using two idealized physically based models. Results suggest that the relationship between the climatological melting-level distribution and the topography is the principle control on the sensitivity of snowpack accumulation to climate warming. It is also shown that, while thermodynamically driven increases in precipitation with warming may moderate the loss of snowfall somewhat, for large amounts of warming increases in precipitation become unimportant, as the loss of accumulation area is too substantial.;Finally, the physical mechanisms acting on the mesoscale to control the mountainside snow line are investigated. On the mountainside, the snow line is often located at an elevation hundreds of meters different from its elevation in the free air upwind. The processes responsible for this behavior are examined in semi-idealized simulations with a mesoscale numerical weather prediction model. Spatial variations in latent cooling from melting precipitation, adiabatic cooling from vertical motion, and the melting distance of frozen hydrometeors are all shown to make important contributions. The relative importance of these processes depends on properties of the incoming flow and terrain geometry. Results suggest an increased depression of the snow line below the upstream 0°C level with increasing temperature, a relationship that, if present in nature, could act to buffer mountain hydroclimate against the impacts of climate warming. |
