The Response of Extreme Precipitation over Idealized Mid-latitude Mountains to Global Warming

Predicting the response of orographic precipitation to global warming is important for human adaptation to and mitigation of future climate changes. The changes in extreme orographic precipitation on the western and eastern slopes of idealized mid-latitude north-south mountain chains under global warming are investigated with a global model and a limited-area model. The global model is used to perform control and double-CO₂ experiments to obtain sets of extreme events, which are further downscaled to domains with higher resolution using the Weather Research and Forecasting (WRF) model. The responses of western-slope precipitation extremes and eastern-slope ones show interesting contrast between them. Western-slope precipitation extremes mostly occur in wintertime, whereas eastern-slope extremes often occur in summer. Western-slope events tend to shift northward under global warming, consistent with the change in mid-latitude storm tracks projected by climate models, whereas eastern-slope events tend to shift southward. The area mean intensity of western slope events in the global model increases by about 3%/K, consistent with the expected change in condensation rate when vertical motions stay constant but moist adiabatic lapse rate of saturation mixing ratio increases as dictated by the Clausius-Clapeyron equation. On the other hand, the area mean intensity of eastern slope events has a sensitivity of about 6%/K, which is significantly enhanced by the stronger vertical motions in warmer climate. The fine distribution of precipitation response as a function of elevation is also investigated using these simulations.