This is a grant under a Climate Variability and Predictability (CLIVAR) Program pilot project called DRICOMP, for the Drought in Coupled Models Project, which focuses on exploring the mechanisms of drought as represented in the output of global climate models and on assessing the reliability of these models in simulating drought.
Historical records of precipitation show distinct multi-decadal variations over East Asia, with a shift around the late 1970s to a pattern often referred to as Southern Flooding and Northern Drought over East China. Associated with this rainfall change, surface air temperatures have cooled during recent decades over central East China, in contrast to the general warming trend in the Northern Hemisphere and the globe. Understanding the causes and physical processes underlying these decadal rainfall changes represents a significant challenge for climate scientists. Recent studies suggest that several factors, including aerosols from air pollution, the Pacific Decadal Oscillation (PDO), and tropical sea surface temperature (SST), may have played a role in causing the recent climate changes over East Asia. There are, however, few detailed studies on the physical mechanisms that can explain the observed climate changes over this region.
The PI has evaluated all the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4) models in terms of their ability to simulate the East Asian Summer Monsoon. They will now study the decadal rainfall changes in East Asia and, in particular, the widespread drought in North China during recent decades. They will focus on analyzing existing and new historical simulations using the National Center for Atmospheric Research (NCAR) and Geophysical Fluid Dynamics Laboratory (GFDL) atmospheric global climate models (GCMs) forced by observed tropical, North Pacific, or global SST only; by East Asian aerosols only; and by greenhouse gases only during the later half of the 20th century. The goal is to quantify the relative role of these individual forcings in causing the observed rainfall changes over East Asia and to diagnose underlying physical processes. Besides examining precipitation and atmospheric circulation fields, other fields such as the Palmer Drought Severity Index will also be computed and analyzed to better characterize the drought in North China. Reanalysis data will also be used and compared with some of the model simulations to help understand atmospheric processes involved. The model analyses will be extended to the IPCC AR4 21st century simulations in order to assess potential future changes in monsoon rainfall and drought severity and extent in East Asia. The results from this project will help evaluate the NCAR and GFDL climate models and improve our knowledge about decadal changes in precipitation and drought over East Asia.
Broader impacts resulting from this project will be to improve our understanding of climate trends and projections in a region of the world that supports the livelihoods of more than a billion people. The project will enable an extended visit to NCAR by a graduate student.
