We simulated the influence of four 2-km high north-south mountain ridges at mid-latitudes on islands in an aqua-planet. While global mean precipitation in simulations increases by 1.6%/K when the CO2 concentration is doubled, the mean precipitation on the windward sides of the mountains increases by 5%/K if mountains are put between 40-60 N, but it becomes the same as global mean response, 1.6%/K, if mountains sit between 35--55 N. In both the 35-55N and 40-60N cases, local precipitation increases larger than 7%/K are reached along the northern parts of the windward sides of mountains. The maximum local increase can be as large as 12%/K. In addition, the frequency of extreme orographic precipitation events at higher mid-latitudes is doubled as temperature increases.
Although orographic precipitation increases faster than CC scaling at northern mid-latitudes, it decreases faster than zonal mean precipitation at southern mid-latitudes. The north-south asymmetry of these responses is related to the poleward shift of storm tracks. To understand changes in orographic precipitation we used a simple diagnostic model, which showed that the changes were mainly determined by three factors: the moist adiabatic lapse rate of saturation specific humidity, the cross-mountain wind component, and the saturated vertical displacement. The first factor is temperature dependent, and it contributed about 4%/K of total changes in orographic precipitation. The other two factors are both affected by storm track shift and thermodynamic changes, so their effects show strong dependence on latitude.