Evaluation of Global Monsoon Precipitation Changes based on Five Reanalysis Datasets

With the motivation to identify whether a reasonably simulated atmospheric circulation would necessarily lead to a successful reproduction of monsoon precipitation, the performances of five sets of reanalysis data [NCEP-U.S. Department of Energy (DOE) Atmospheric Model Intercomparison Project II (AMIP-II) reanalysis (NCEP-2), 40-yr ECMWF Re-Analysis (ERA-40), Japanese 25-yr Reanalysis Project (JRA-25), Interim ECMWF Re-Analysis (ERA-Interim), and Modern-Era Retrospective Analysis for Research and Applications (MERRA)] in reproducing the climatology, interannual variation, and long-term trend of global monsoon (GM) precipitation are comprehensively evaluated. To better understand the variability and long-term trend of GM precipitation, the authors also examined the major components of water budget, including evaporation, water vapor convergence, and the change in local column water vapor, based on the five reanalysis datasets. Results show that all five reanalysis datasets reasonably reproduce the climatology of GM precipitation. ERA-Interim (NCEP-2) shows the highest (lowest) skill among the five datasets. The observed GM precipitation shows an increasing tendency during 1979-2011 along with a strong interannual variability, which is reasonably reproduced by five reanalysis datasets. The observed increasing trend of GM precipitation is dominated by contributions from the Asian, North American, Southern African, and Australian monsoons. All five datasets fail in reproducing the increasing tendency of the North African monsoon precipitation. The wind convergence term in the water budget equation dominates the GM precipitation variation, indicating a consistency between the GM precipitation and the seasonal change of prevailing wind.