Northwestern China summer precipitation change in response to uniform oceanic warming

Potential summer precipitation change over the Northwestern China caused by global warming is of paramount importance to the local population. 12 climate models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) show huge divergence in the precipitation responses to 4-K uniform sea surface temperature warming, ranging from severe drying to wettening. A series of experiments using two Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric models, which differs only in convective parameterization, are performed to explore the underlying mechanisms of the discrepancies among climate model projections. In response to 2-K warming, one model produces a 25% reduction in summer precipitation over the northwestern China, while the other a 3% increase. The key to understanding the difference lies in the upper-tropospheric synoptic disturbances. Their activity tends to weaken locally over the southwestern China owing to the poleward shift of the storm track, posing a local drying effect. The other factor is the enhancement of synoptic activities over North Atlantic. When drifting downstream (westward), stronger disturbances counteract the local weakening, giving rise to a remote wettening effect. The sign of precipitation change depends on which effect wins out. The use of observations for emergent constraints and the implications for rationalizing the hydroclimate changes over other dry land regions are discussed.