Air Pollution or Global Warming: Attribution of Extreme Precipitation Changes in Eastern China

The widely observed phenomena of suppressed light precipitation and enhanced heavy precipitation represent a critical issue for understanding of changes in climate and the global hydrological cycle. As the two major forcing agents in the climate system, greenhouse gases and anthropogenic aerosols have been inevitably linked to the modification of precipitation intensity in many previous studies. However, the attribution of the observed changes in extreme precipitation to the forcing components remains an open question and under considerable debate, especially on the regional scale. To tease out aerosol effects on the historical precipitation trends, the AMIP-style NCAR/DOE CAM5 model simulations are performed from 1950-2005 with and without aerosol forcings. Hourly precipitation rates in CAM5 are used to construct monthly precipitation probability distribution functions at each grid point. By contrasting the two set of experiments, we found that although global warming caused by increasing green-house gases likely induces a adjustment in moisture availability and precipitation intensity at the global scale, the dramatic variations of anthropogenic aerosols and the wide range of aerosol forcings complicate the role of the global warming at the regional scale. Our model simulations suggest that the increased anthropogenic aerosols rather than the accumulated greenhouse gases in East China since the 1960s accounts for the observed the light precipitation suppression.