Future change of precipitation-altitude relationship over the Asian summer monsoon region simulated by a high-resolution climate model with a time-slice technique

We examine the possible future change of precipitation-altitude relationship over the Asian summer monsoon region simulated by a high-resolution (about 60 km grid spacing) climate model with a time-slice technique. In order to estimate statistical robustness, we conduct a set of ensemble simulations for both present-day and future climate by the combination of different initial conditions and different SSTs from atmosphere-ocean coupled global climate models (CGCM) with different climate sensitivities derived from CMIP3 datasets. Possible future change of precipitation-altitude relationship, described by the ratio of mean precipitation in future climate to that in present-day in each altitude bands, shows that mean precipitation in future climate increases in all altitudes and that the change depends on altitude. The change in low altitudes (<1,500m) and high altitudes (>4,000m) is larger than that in middle altitudes (1,500~4,000m). Atmospheric water budget analysis shows that both surface evaporation and atmospheric water vapor flux convergence are positive in all altitudes in the present-day climate simulations. In future climate simulations, surface evaporation increase mostly accounts for precipitation increase in high altitudes. Surface evaporation increase in high altitudes would be attributed to the mechanisms below: (1) snowfall changes into rainfall due to temperature warming, (2) temperature warming plus rainfall increase lead to a reduction of snow cover, (3) reduction of snow cover results in the increase of evaporation from the surface, (4) the increase of surface evaporation, as well as the increase of atmospheric water vapor convergence, leads to precipitation increase in high altitude.